Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing...

43
Interaction of Ionizing Radiation with Matter 1 Type of radiation charged particles photonen neutronen Uncharged „particles“ Charged particles electrons (β - ) He 2+ (α), H + (p) D + (d) Recoil nuclides Fission fragments Interaction of ionizing radiation with matter can be described at the molecular level (molecular process) or as macroscopic effects ( decrease, absorption, scattering, etc.)

Transcript of Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing...

Page 1: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

1

Type of radiationcharged particles

photonenneutronen Uncharged bdquoparticlesldquo

Charged particleselectrons (β-)

He2+ (α) H+(p) D+ (d)Recoil nuclidesFission fragments

Interaction of ionizing radiation with matter can be described at the molecular level (molecular process)

or as macroscopic effects ( decrease absorption scattering etc)

Interaction of Ionizing Radiation with Matter

2

Radiation deceleration decrease of energy

Matter physical chemical andor biological effects

Important parameters

Practical consequences of the interaction with matter

particle mass chargespeed kinetic energyspin

matter

atom mass Atom number Znumber of e- per volumedensityionization potential

Interaction of Ionizing Radiation with Matter

3

Synopsis of interactions with the electron shell

photonsphoto effectcompton effect

charged particles scattering ionization

Interaction of Ionizing Radiation with Matter

4

Synopsis of interactions with the atomic nucleus

pair formationnuclear reaction

charged particles scattering Bremsstrahlung nuclear reaction

photons

Interaction of Ionizing Radiation with Matter

5

Energy is high enough to ionize by collision

Indirect ionizing radiation n γ

Ionization as a consequents of nuclear reactions in the absorbing matter

In the context of radiation absorption two definitions are important

linear stopping power

and linear energy transfer

Without Bremsstrahlung SI and LI are equal otherwise there will be a substantial difference

also important

Ionizing radiation

Direct ionizing radiation α β- β+ hellip

Interaction of Ionizing Radiation with Matter

6

Charged particles deceleration by inelastic scattering

Ionization and Excitation

Ionizing radiation

Interaction of Ionizing Radiation with Matter

7

By collision with electrons the incident particle ionizes matter

The mean energy to remove an electron is called the W-factor

W-factor for air is 3385eVIP

When the charged particle travels through matter it makes an energy dependent number of ionization length

this is called specific ionization (SI)

The mean energy loss per path length (LET) can determined by

LET = SI∙W LET = Linear Energy Transfer

Ionizing radiation

Interaction of Ionizing Radiation with Matter

8

Ionizing radiation

The lower the energy the higher the SI since probability of interaction with shell electron increases

Bragg Peak

Interaction of Ionizing Radiation with Matter

9

241 Am was in smoke detectors Eα= 548 MeV

specific ionization (SI) = 34sdot104 IPcm

LET = 34middot104middot338 = 12 MeVcm

Range = = = 48 cm

This is the maximum range the SI increases dramatically at the end of the path

Ionizing radiation

Example

Interaction of Ionizing Radiation with Matter

10

RSP = RairRabs (R = Range)

RSP values for some materials and particles

SI is a characteristic feature of a specific material since the e--density changesTo compare different materials the relative stopping power is useful

Ionizing radiation

Interaction of Ionizing Radiation with Matter

11

Ionizing radiation

Ranges in air for different particles and energies

Interaction of Ionizing Radiation with Matter

12

Since not every collision leads to ionization the average energy loss for ionization is larger than the minimal Ie of the atoms

Bethe and Bloch proposed a bdquosimpleldquo formula for energy loss along a track considering the nature of the absorber

The most important interaction of electrons with matter is inelastic scattering with electrons from the shells

Interaction of electrons with matter

ionization

Interaction of Ionizing Radiation with Matter

13

me = rest mass of an electronε0 = dielectric constant (vacuum)ν = velocity of the electronT = mean ionization density of the matterial

e- are light particles relativistic effects have to be considered

E = 100 keVE = 1000 keV

v = 055 cv = 094 c

m = 12 ∙ mo

m = 3 ∙ mo

for lower energies the relativistic effects can be neglected

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 2: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

2

Radiation deceleration decrease of energy

Matter physical chemical andor biological effects

Important parameters

Practical consequences of the interaction with matter

particle mass chargespeed kinetic energyspin

matter

atom mass Atom number Znumber of e- per volumedensityionization potential

Interaction of Ionizing Radiation with Matter

3

Synopsis of interactions with the electron shell

photonsphoto effectcompton effect

charged particles scattering ionization

Interaction of Ionizing Radiation with Matter

4

Synopsis of interactions with the atomic nucleus

pair formationnuclear reaction

charged particles scattering Bremsstrahlung nuclear reaction

photons

Interaction of Ionizing Radiation with Matter

5

Energy is high enough to ionize by collision

Indirect ionizing radiation n γ

Ionization as a consequents of nuclear reactions in the absorbing matter

In the context of radiation absorption two definitions are important

linear stopping power

and linear energy transfer

Without Bremsstrahlung SI and LI are equal otherwise there will be a substantial difference

also important

Ionizing radiation

Direct ionizing radiation α β- β+ hellip

Interaction of Ionizing Radiation with Matter

6

Charged particles deceleration by inelastic scattering

Ionization and Excitation

Ionizing radiation

Interaction of Ionizing Radiation with Matter

7

By collision with electrons the incident particle ionizes matter

The mean energy to remove an electron is called the W-factor

W-factor for air is 3385eVIP

When the charged particle travels through matter it makes an energy dependent number of ionization length

this is called specific ionization (SI)

The mean energy loss per path length (LET) can determined by

LET = SI∙W LET = Linear Energy Transfer

Ionizing radiation

Interaction of Ionizing Radiation with Matter

8

Ionizing radiation

The lower the energy the higher the SI since probability of interaction with shell electron increases

Bragg Peak

Interaction of Ionizing Radiation with Matter

9

241 Am was in smoke detectors Eα= 548 MeV

specific ionization (SI) = 34sdot104 IPcm

LET = 34middot104middot338 = 12 MeVcm

Range = = = 48 cm

This is the maximum range the SI increases dramatically at the end of the path

Ionizing radiation

Example

Interaction of Ionizing Radiation with Matter

10

RSP = RairRabs (R = Range)

RSP values for some materials and particles

SI is a characteristic feature of a specific material since the e--density changesTo compare different materials the relative stopping power is useful

Ionizing radiation

Interaction of Ionizing Radiation with Matter

11

Ionizing radiation

Ranges in air for different particles and energies

Interaction of Ionizing Radiation with Matter

12

Since not every collision leads to ionization the average energy loss for ionization is larger than the minimal Ie of the atoms

Bethe and Bloch proposed a bdquosimpleldquo formula for energy loss along a track considering the nature of the absorber

The most important interaction of electrons with matter is inelastic scattering with electrons from the shells

Interaction of electrons with matter

ionization

Interaction of Ionizing Radiation with Matter

13

me = rest mass of an electronε0 = dielectric constant (vacuum)ν = velocity of the electronT = mean ionization density of the matterial

e- are light particles relativistic effects have to be considered

E = 100 keVE = 1000 keV

v = 055 cv = 094 c

m = 12 ∙ mo

m = 3 ∙ mo

for lower energies the relativistic effects can be neglected

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 3: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

3

Synopsis of interactions with the electron shell

photonsphoto effectcompton effect

charged particles scattering ionization

Interaction of Ionizing Radiation with Matter

4

Synopsis of interactions with the atomic nucleus

pair formationnuclear reaction

charged particles scattering Bremsstrahlung nuclear reaction

photons

Interaction of Ionizing Radiation with Matter

5

Energy is high enough to ionize by collision

Indirect ionizing radiation n γ

Ionization as a consequents of nuclear reactions in the absorbing matter

In the context of radiation absorption two definitions are important

linear stopping power

and linear energy transfer

Without Bremsstrahlung SI and LI are equal otherwise there will be a substantial difference

also important

Ionizing radiation

Direct ionizing radiation α β- β+ hellip

Interaction of Ionizing Radiation with Matter

6

Charged particles deceleration by inelastic scattering

Ionization and Excitation

Ionizing radiation

Interaction of Ionizing Radiation with Matter

7

By collision with electrons the incident particle ionizes matter

The mean energy to remove an electron is called the W-factor

W-factor for air is 3385eVIP

When the charged particle travels through matter it makes an energy dependent number of ionization length

this is called specific ionization (SI)

The mean energy loss per path length (LET) can determined by

LET = SI∙W LET = Linear Energy Transfer

Ionizing radiation

Interaction of Ionizing Radiation with Matter

8

Ionizing radiation

The lower the energy the higher the SI since probability of interaction with shell electron increases

Bragg Peak

Interaction of Ionizing Radiation with Matter

9

241 Am was in smoke detectors Eα= 548 MeV

specific ionization (SI) = 34sdot104 IPcm

LET = 34middot104middot338 = 12 MeVcm

Range = = = 48 cm

This is the maximum range the SI increases dramatically at the end of the path

Ionizing radiation

Example

Interaction of Ionizing Radiation with Matter

10

RSP = RairRabs (R = Range)

RSP values for some materials and particles

SI is a characteristic feature of a specific material since the e--density changesTo compare different materials the relative stopping power is useful

Ionizing radiation

Interaction of Ionizing Radiation with Matter

11

Ionizing radiation

Ranges in air for different particles and energies

Interaction of Ionizing Radiation with Matter

12

Since not every collision leads to ionization the average energy loss for ionization is larger than the minimal Ie of the atoms

Bethe and Bloch proposed a bdquosimpleldquo formula for energy loss along a track considering the nature of the absorber

The most important interaction of electrons with matter is inelastic scattering with electrons from the shells

Interaction of electrons with matter

ionization

Interaction of Ionizing Radiation with Matter

13

me = rest mass of an electronε0 = dielectric constant (vacuum)ν = velocity of the electronT = mean ionization density of the matterial

e- are light particles relativistic effects have to be considered

E = 100 keVE = 1000 keV

v = 055 cv = 094 c

m = 12 ∙ mo

m = 3 ∙ mo

for lower energies the relativistic effects can be neglected

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 4: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

4

Synopsis of interactions with the atomic nucleus

pair formationnuclear reaction

charged particles scattering Bremsstrahlung nuclear reaction

photons

Interaction of Ionizing Radiation with Matter

5

Energy is high enough to ionize by collision

Indirect ionizing radiation n γ

Ionization as a consequents of nuclear reactions in the absorbing matter

In the context of radiation absorption two definitions are important

linear stopping power

and linear energy transfer

Without Bremsstrahlung SI and LI are equal otherwise there will be a substantial difference

also important

Ionizing radiation

Direct ionizing radiation α β- β+ hellip

Interaction of Ionizing Radiation with Matter

6

Charged particles deceleration by inelastic scattering

Ionization and Excitation

Ionizing radiation

Interaction of Ionizing Radiation with Matter

7

By collision with electrons the incident particle ionizes matter

The mean energy to remove an electron is called the W-factor

W-factor for air is 3385eVIP

When the charged particle travels through matter it makes an energy dependent number of ionization length

this is called specific ionization (SI)

The mean energy loss per path length (LET) can determined by

LET = SI∙W LET = Linear Energy Transfer

Ionizing radiation

Interaction of Ionizing Radiation with Matter

8

Ionizing radiation

The lower the energy the higher the SI since probability of interaction with shell electron increases

Bragg Peak

Interaction of Ionizing Radiation with Matter

9

241 Am was in smoke detectors Eα= 548 MeV

specific ionization (SI) = 34sdot104 IPcm

LET = 34middot104middot338 = 12 MeVcm

Range = = = 48 cm

This is the maximum range the SI increases dramatically at the end of the path

Ionizing radiation

Example

Interaction of Ionizing Radiation with Matter

10

RSP = RairRabs (R = Range)

RSP values for some materials and particles

SI is a characteristic feature of a specific material since the e--density changesTo compare different materials the relative stopping power is useful

Ionizing radiation

Interaction of Ionizing Radiation with Matter

11

Ionizing radiation

Ranges in air for different particles and energies

Interaction of Ionizing Radiation with Matter

12

Since not every collision leads to ionization the average energy loss for ionization is larger than the minimal Ie of the atoms

Bethe and Bloch proposed a bdquosimpleldquo formula for energy loss along a track considering the nature of the absorber

The most important interaction of electrons with matter is inelastic scattering with electrons from the shells

Interaction of electrons with matter

ionization

Interaction of Ionizing Radiation with Matter

13

me = rest mass of an electronε0 = dielectric constant (vacuum)ν = velocity of the electronT = mean ionization density of the matterial

e- are light particles relativistic effects have to be considered

E = 100 keVE = 1000 keV

v = 055 cv = 094 c

m = 12 ∙ mo

m = 3 ∙ mo

for lower energies the relativistic effects can be neglected

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 5: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

5

Energy is high enough to ionize by collision

Indirect ionizing radiation n γ

Ionization as a consequents of nuclear reactions in the absorbing matter

In the context of radiation absorption two definitions are important

linear stopping power

and linear energy transfer

Without Bremsstrahlung SI and LI are equal otherwise there will be a substantial difference

also important

Ionizing radiation

Direct ionizing radiation α β- β+ hellip

Interaction of Ionizing Radiation with Matter

6

Charged particles deceleration by inelastic scattering

Ionization and Excitation

Ionizing radiation

Interaction of Ionizing Radiation with Matter

7

By collision with electrons the incident particle ionizes matter

The mean energy to remove an electron is called the W-factor

W-factor for air is 3385eVIP

When the charged particle travels through matter it makes an energy dependent number of ionization length

this is called specific ionization (SI)

The mean energy loss per path length (LET) can determined by

LET = SI∙W LET = Linear Energy Transfer

Ionizing radiation

Interaction of Ionizing Radiation with Matter

8

Ionizing radiation

The lower the energy the higher the SI since probability of interaction with shell electron increases

Bragg Peak

Interaction of Ionizing Radiation with Matter

9

241 Am was in smoke detectors Eα= 548 MeV

specific ionization (SI) = 34sdot104 IPcm

LET = 34middot104middot338 = 12 MeVcm

Range = = = 48 cm

This is the maximum range the SI increases dramatically at the end of the path

Ionizing radiation

Example

Interaction of Ionizing Radiation with Matter

10

RSP = RairRabs (R = Range)

RSP values for some materials and particles

SI is a characteristic feature of a specific material since the e--density changesTo compare different materials the relative stopping power is useful

Ionizing radiation

Interaction of Ionizing Radiation with Matter

11

Ionizing radiation

Ranges in air for different particles and energies

Interaction of Ionizing Radiation with Matter

12

Since not every collision leads to ionization the average energy loss for ionization is larger than the minimal Ie of the atoms

Bethe and Bloch proposed a bdquosimpleldquo formula for energy loss along a track considering the nature of the absorber

The most important interaction of electrons with matter is inelastic scattering with electrons from the shells

Interaction of electrons with matter

ionization

Interaction of Ionizing Radiation with Matter

13

me = rest mass of an electronε0 = dielectric constant (vacuum)ν = velocity of the electronT = mean ionization density of the matterial

e- are light particles relativistic effects have to be considered

E = 100 keVE = 1000 keV

v = 055 cv = 094 c

m = 12 ∙ mo

m = 3 ∙ mo

for lower energies the relativistic effects can be neglected

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 6: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

6

Charged particles deceleration by inelastic scattering

Ionization and Excitation

Ionizing radiation

Interaction of Ionizing Radiation with Matter

7

By collision with electrons the incident particle ionizes matter

The mean energy to remove an electron is called the W-factor

W-factor for air is 3385eVIP

When the charged particle travels through matter it makes an energy dependent number of ionization length

this is called specific ionization (SI)

The mean energy loss per path length (LET) can determined by

LET = SI∙W LET = Linear Energy Transfer

Ionizing radiation

Interaction of Ionizing Radiation with Matter

8

Ionizing radiation

The lower the energy the higher the SI since probability of interaction with shell electron increases

Bragg Peak

Interaction of Ionizing Radiation with Matter

9

241 Am was in smoke detectors Eα= 548 MeV

specific ionization (SI) = 34sdot104 IPcm

LET = 34middot104middot338 = 12 MeVcm

Range = = = 48 cm

This is the maximum range the SI increases dramatically at the end of the path

Ionizing radiation

Example

Interaction of Ionizing Radiation with Matter

10

RSP = RairRabs (R = Range)

RSP values for some materials and particles

SI is a characteristic feature of a specific material since the e--density changesTo compare different materials the relative stopping power is useful

Ionizing radiation

Interaction of Ionizing Radiation with Matter

11

Ionizing radiation

Ranges in air for different particles and energies

Interaction of Ionizing Radiation with Matter

12

Since not every collision leads to ionization the average energy loss for ionization is larger than the minimal Ie of the atoms

Bethe and Bloch proposed a bdquosimpleldquo formula for energy loss along a track considering the nature of the absorber

The most important interaction of electrons with matter is inelastic scattering with electrons from the shells

Interaction of electrons with matter

ionization

Interaction of Ionizing Radiation with Matter

13

me = rest mass of an electronε0 = dielectric constant (vacuum)ν = velocity of the electronT = mean ionization density of the matterial

e- are light particles relativistic effects have to be considered

E = 100 keVE = 1000 keV

v = 055 cv = 094 c

m = 12 ∙ mo

m = 3 ∙ mo

for lower energies the relativistic effects can be neglected

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 7: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

7

By collision with electrons the incident particle ionizes matter

The mean energy to remove an electron is called the W-factor

W-factor for air is 3385eVIP

When the charged particle travels through matter it makes an energy dependent number of ionization length

this is called specific ionization (SI)

The mean energy loss per path length (LET) can determined by

LET = SI∙W LET = Linear Energy Transfer

Ionizing radiation

Interaction of Ionizing Radiation with Matter

8

Ionizing radiation

The lower the energy the higher the SI since probability of interaction with shell electron increases

Bragg Peak

Interaction of Ionizing Radiation with Matter

9

241 Am was in smoke detectors Eα= 548 MeV

specific ionization (SI) = 34sdot104 IPcm

LET = 34middot104middot338 = 12 MeVcm

Range = = = 48 cm

This is the maximum range the SI increases dramatically at the end of the path

Ionizing radiation

Example

Interaction of Ionizing Radiation with Matter

10

RSP = RairRabs (R = Range)

RSP values for some materials and particles

SI is a characteristic feature of a specific material since the e--density changesTo compare different materials the relative stopping power is useful

Ionizing radiation

Interaction of Ionizing Radiation with Matter

11

Ionizing radiation

Ranges in air for different particles and energies

Interaction of Ionizing Radiation with Matter

12

Since not every collision leads to ionization the average energy loss for ionization is larger than the minimal Ie of the atoms

Bethe and Bloch proposed a bdquosimpleldquo formula for energy loss along a track considering the nature of the absorber

The most important interaction of electrons with matter is inelastic scattering with electrons from the shells

Interaction of electrons with matter

ionization

Interaction of Ionizing Radiation with Matter

13

me = rest mass of an electronε0 = dielectric constant (vacuum)ν = velocity of the electronT = mean ionization density of the matterial

e- are light particles relativistic effects have to be considered

E = 100 keVE = 1000 keV

v = 055 cv = 094 c

m = 12 ∙ mo

m = 3 ∙ mo

for lower energies the relativistic effects can be neglected

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 8: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

8

Ionizing radiation

The lower the energy the higher the SI since probability of interaction with shell electron increases

Bragg Peak

Interaction of Ionizing Radiation with Matter

9

241 Am was in smoke detectors Eα= 548 MeV

specific ionization (SI) = 34sdot104 IPcm

LET = 34middot104middot338 = 12 MeVcm

Range = = = 48 cm

This is the maximum range the SI increases dramatically at the end of the path

Ionizing radiation

Example

Interaction of Ionizing Radiation with Matter

10

RSP = RairRabs (R = Range)

RSP values for some materials and particles

SI is a characteristic feature of a specific material since the e--density changesTo compare different materials the relative stopping power is useful

Ionizing radiation

Interaction of Ionizing Radiation with Matter

11

Ionizing radiation

Ranges in air for different particles and energies

Interaction of Ionizing Radiation with Matter

12

Since not every collision leads to ionization the average energy loss for ionization is larger than the minimal Ie of the atoms

Bethe and Bloch proposed a bdquosimpleldquo formula for energy loss along a track considering the nature of the absorber

The most important interaction of electrons with matter is inelastic scattering with electrons from the shells

Interaction of electrons with matter

ionization

Interaction of Ionizing Radiation with Matter

13

me = rest mass of an electronε0 = dielectric constant (vacuum)ν = velocity of the electronT = mean ionization density of the matterial

e- are light particles relativistic effects have to be considered

E = 100 keVE = 1000 keV

v = 055 cv = 094 c

m = 12 ∙ mo

m = 3 ∙ mo

for lower energies the relativistic effects can be neglected

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 9: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

9

241 Am was in smoke detectors Eα= 548 MeV

specific ionization (SI) = 34sdot104 IPcm

LET = 34middot104middot338 = 12 MeVcm

Range = = = 48 cm

This is the maximum range the SI increases dramatically at the end of the path

Ionizing radiation

Example

Interaction of Ionizing Radiation with Matter

10

RSP = RairRabs (R = Range)

RSP values for some materials and particles

SI is a characteristic feature of a specific material since the e--density changesTo compare different materials the relative stopping power is useful

Ionizing radiation

Interaction of Ionizing Radiation with Matter

11

Ionizing radiation

Ranges in air for different particles and energies

Interaction of Ionizing Radiation with Matter

12

Since not every collision leads to ionization the average energy loss for ionization is larger than the minimal Ie of the atoms

Bethe and Bloch proposed a bdquosimpleldquo formula for energy loss along a track considering the nature of the absorber

The most important interaction of electrons with matter is inelastic scattering with electrons from the shells

Interaction of electrons with matter

ionization

Interaction of Ionizing Radiation with Matter

13

me = rest mass of an electronε0 = dielectric constant (vacuum)ν = velocity of the electronT = mean ionization density of the matterial

e- are light particles relativistic effects have to be considered

E = 100 keVE = 1000 keV

v = 055 cv = 094 c

m = 12 ∙ mo

m = 3 ∙ mo

for lower energies the relativistic effects can be neglected

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 10: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

10

RSP = RairRabs (R = Range)

RSP values for some materials and particles

SI is a characteristic feature of a specific material since the e--density changesTo compare different materials the relative stopping power is useful

Ionizing radiation

Interaction of Ionizing Radiation with Matter

11

Ionizing radiation

Ranges in air for different particles and energies

Interaction of Ionizing Radiation with Matter

12

Since not every collision leads to ionization the average energy loss for ionization is larger than the minimal Ie of the atoms

Bethe and Bloch proposed a bdquosimpleldquo formula for energy loss along a track considering the nature of the absorber

The most important interaction of electrons with matter is inelastic scattering with electrons from the shells

Interaction of electrons with matter

ionization

Interaction of Ionizing Radiation with Matter

13

me = rest mass of an electronε0 = dielectric constant (vacuum)ν = velocity of the electronT = mean ionization density of the matterial

e- are light particles relativistic effects have to be considered

E = 100 keVE = 1000 keV

v = 055 cv = 094 c

m = 12 ∙ mo

m = 3 ∙ mo

for lower energies the relativistic effects can be neglected

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 11: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

11

Ionizing radiation

Ranges in air for different particles and energies

Interaction of Ionizing Radiation with Matter

12

Since not every collision leads to ionization the average energy loss for ionization is larger than the minimal Ie of the atoms

Bethe and Bloch proposed a bdquosimpleldquo formula for energy loss along a track considering the nature of the absorber

The most important interaction of electrons with matter is inelastic scattering with electrons from the shells

Interaction of electrons with matter

ionization

Interaction of Ionizing Radiation with Matter

13

me = rest mass of an electronε0 = dielectric constant (vacuum)ν = velocity of the electronT = mean ionization density of the matterial

e- are light particles relativistic effects have to be considered

E = 100 keVE = 1000 keV

v = 055 cv = 094 c

m = 12 ∙ mo

m = 3 ∙ mo

for lower energies the relativistic effects can be neglected

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 12: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

12

Since not every collision leads to ionization the average energy loss for ionization is larger than the minimal Ie of the atoms

Bethe and Bloch proposed a bdquosimpleldquo formula for energy loss along a track considering the nature of the absorber

The most important interaction of electrons with matter is inelastic scattering with electrons from the shells

Interaction of electrons with matter

ionization

Interaction of Ionizing Radiation with Matter

13

me = rest mass of an electronε0 = dielectric constant (vacuum)ν = velocity of the electronT = mean ionization density of the matterial

e- are light particles relativistic effects have to be considered

E = 100 keVE = 1000 keV

v = 055 cv = 094 c

m = 12 ∙ mo

m = 3 ∙ mo

for lower energies the relativistic effects can be neglected

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 13: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

13

me = rest mass of an electronε0 = dielectric constant (vacuum)ν = velocity of the electronT = mean ionization density of the matterial

e- are light particles relativistic effects have to be considered

E = 100 keVE = 1000 keV

v = 055 cv = 094 c

m = 12 ∙ mo

m = 3 ∙ mo

for lower energies the relativistic effects can be neglected

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 14: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

14

The formula predict a minimum value

depending only on the mass of the particle

The slower the particle the more ionization per length

dEdx at a certain energy

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 15: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

15

Typical β- decay shows a continuous energy distribution hence it has many low energy electrons

Ψ(x) = Ψ(0) ∙ e-micro∙x

with micro = konst

or N(x) = N0 ∙ e-micro∙x

with micro = linear absorption coefficient (see x-ray crystallography)

The Bethe-Bloch formula is an exponential formula

Interaction of electrons with matter

Empirically it can be described

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 16: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

16

The absorption of electrons decreases linearly

Often instead of path x one takes mass-equivalent range d = δ∙ x

then

with microδ = mass absorption coefficient

it allows to calculate the maximum range of electrons in a material

it allows to calculate the thickness of materials for shielding

Interaction of electrons with matter

micro is a function of the electron energy and the material

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 17: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

17

Example equivalent range of e- in Al

one can easily calculate the path for reducing the e--flux to 50

x12 can be determined experimentally and micro be calculated for a particular material

andx12 = ln2micro

d12 = (ln2)(micro8)

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 18: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

18

Semiempirical relationships for connecting range with electron energy

(015 lt Eβ lt 08 MeV)

Interaction of electrons with matter

Semiempirical relationship between micro δ and Emax

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 19: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

19

Maximum ranges of different β-emitters

Interaction of electrons with matter

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 20: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

20

How much energy can be lost in a single collision

Of particular interest collision with a shell electron

Maximum energy transfer

incoming particle mass Mi speed Vi1

electron mass me speed 0

after collision Mi v2 me ve

Energy frac12 Mimiddotv12 = frac12 Mimiddotv2

2 + frac12 memiddot ve2

momentum Mi middotv1 = Miv2 + memiddotve (non-relativistic)

Interaction of charged particles with matter

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 21: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

21

speed of reflected particle

MET Qmax = nicht relativistisch

If Mi = me (electron on electron)

then Qmax = E

This explains why light particles have a zigzag pass in matter

α-particle colliding with an e-

me = 9109∙10-31 kg mα = 6646∙10-27 kg 5468 ∙10-4 u 40026 u

QmaxE = = 000054 = 005 heavy particles travel straight

Maximum energy transfer (MET)

Example

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 22: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

22

Examples for protons H

Proton KineticEnergy E(MeV)

011

10100

103

104

105

106

107

Qmax(MeV)

00002200022002190229333136106 x 104

538 x 105

921 x 106

Maximum percentageenergy transfer

100QmaxE

02202202202303314

106538921

Maximum energy transfer (MET)

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 23: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

23

Which results in the emission of Bremsstrahlung

Bremsstrahlung

Besides inelastic scattering at the electron shell inelasting scattering at the nucleus is the most important interaction

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 24: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

24

The stopping power of atoms or materials does not only depend on ionization but also on direct electron-target nucleus interactions

This energy loss generates photons so called Bremsstrahlung

total stopping power

From Bethe-Formula the ratio between collision and radiation is

The higher the atomic number the more Bremsstrahlung

Bremsstrahlung

The higher the energy the more Bremsstrahlung

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 25: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

25

The following formula gives this ratio

Example Pb shielded source of 90Y(Emax = 228MeV) produces 10 Bremsstrahlung

Bremsstrahlung

The stopping efficiency by Bremsstrahlung increases by z2 but the stopping by ionization only by z

The formation of Bremsstrahlung increases with the energy of the electron

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 26: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

26

Bremsstrahlung

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 27: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

27

Example

Bremsstrahlung

Pb shielded source of 90Y(Emax = 228MeV) produces asymp10 Bremsstrahlung

Donlsquot shield β-emitters with lead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 28: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

28

The Bremsstrahlung is used to produce synchrotron radiation

Bremsstrahlung

Synchrotron Lichtquelle Schweiz SLS

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 29: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

29

Photo Effect

Compton EffectPair Formation

Three principle modes of interaction

Photons do not steadily lose energy as they penetrate matter

The distance the photons can travel before they interact with anatom is governed statistically by a probability which depends onthe specific medium and on the photon energy

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 30: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

30

electron gap filled by an outer-sphere electron (X-ray fluorescence secondary radiation)

Photo effect

incoming γ-quant

photoelectron

interaction between γ - quanta and electrons of the inner shellsemission of a photoelectron (ionization)dominates with low photon energiesabsorption of the γ -quant

Electron of the shell

higher energy level

lower energylevel γ-quant

radiation

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 31: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

31

The photoelectron contains the complete energy of the γ ndash quant minus anenergy ϕ that the electron expends in escaping the atom

Every γ-rays emitting nucleus emits γ-quanta with a distinct energies (fingerprint)

γ ndash spectroscopy

ϕν minus= hT

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Photo effect

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 32: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

32

The photo effect depends strongly on the atomic number Z and theenergy hν of the photons

3)(4

νhZyprobabilit =

Photo effect

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 33: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

33

interaction between γ -quanta and e- of the outer electron shells (Compton electrons)

emission of a Compton electron (ionization)

γ -quant loses energy (shift to longer wavelengths Compton shift)

the Compton shift only depends on the scattered angle not on the wave length of the incident-photon

resulting quant can undergo more Compton reaction or finally photo reactions

Compton effect

Incomingγ-quant

scatteredγ-quant

compton electron

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 34: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

34

The emitted Compton electrons have no defined energy (Compton continuum)

Compton continuum

httpenwikipediaorgwikiFileGammaspektrum_Uranerzjpg

Compton effect

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 35: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

35

Never forget 2cmE sdot=

A photon with an energy of at least 1022 MeV can be converted into an e+ e-

pair in the field of an atomic nucleus

22 cemh geν

Excess energy is kinetic energy of the products

The distribution of the excess energy is continuous

Pair formation

incoming γ-quant

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 36: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

36

Pair production becomes more likely with increasing photon energy

The probability also increases with the atomic number

2Zyprobabilit asymp

Pair formation

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 37: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

37

The produced positron immediately reacts with an electron

νhee =minus++

Since the total momentum before the decay is zero two photons mustbe produced in order to conserve momentum

The produced photons going off in opposite directions

νhcem =22Due to the photon energy is 511 keV (1022 MeV2)

Annihilation of positrons

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 38: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

38

The presents of 511 keV annihilation photons around any positron source is always a potential radiation hazard

Disadvantage

AdvantagesPair Formation helps to convert high energy photons (gt 1022 MeV) into photons with less energy (511 keV)

rArr easier to shield

Question How would you shield a γ-emitter

Pair formation

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 39: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

12032018

Interaction of γ-radiation and x-rays with matter

Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 40: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

40

Neutrons have no charge and donlsquot interact with the shell electron (no direct ionization)

Classification of Neutrons

Thermal Neutrons Energy distribution according to the Maxwell ndash Boltzmann equationEnergy asymp 0025 eV

(most probable energy in the distribution at 20degC)

Slow Neutrons Also called ldquointermediaterdquo of ldquoresonancerdquo neutronsEnergy le 01 MeV

Fast Neutrons Energy le 20 MeV

Relativistic Neutrons Energy gt 20 MeV

Interaction of neutrons with matter

Interactions between neutrons and matter are interactions with nuclei (only secondary ionization processes)

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 41: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

41

energy range 1 - 10 MeVemission of excess energy as γ-quants

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

fast neutronW1

slow neutronW2

Backscattered nucleus W3 γ-quant

Inelastic scattering

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 42: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

42

Interaction of neutrons with matter

fast neutronW1

slow neutronW2

Backscattered nucleusW3

Elastic scattering

2)(4

max mMnmMEQ

+=

M = Mass of a neutronm = Mass of the recoil nucleusEn = Kinetic energy of the neutron

Maximum Fraction of Energy Lost Qmax En

energy range 10 keV - 1 MeV

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
Page 43: Interaction of Ionizing Radiation with Matter95d7c5c8-704c-48bc... · Interaction of Ionizing Radiation with Matter. 16. The absorption of electrons decreases linearly Often, instead

Interaction of Ionizing Radiation with Matter

43

If a neutron reaches thermal energies it will move about randomly by elastic scattering until absorbed by a nucleus

Slowing-down neutrons is called neutron moderation

Nuclear reaction (np) (n 2n) (n α) (n γ)

Neutron Activation Analysis

Interaction of neutrons with matter

  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter
  • Interaction of Ionizing Radiation with Matter