C h a p t e rC h a p t e r C h a p t e rC h a p t e r 22 Nuclear Chemistry Brain images with 123...

C h a p t e rC h a p t e r 2222Nuclear ChemistryNuclear Chemistry

Brain images with 123I-labeled (γ-emitter) compound

Chapter 22 Slide 2

Use of 131I (β-emitter) in detecting Hyper- or hypo- thyroidism

Chapter 22 Slide 3

© 2003 John Wiley and Sons Publishers

Henri Becquerel March 1, 1896 :

Chapter 22 Slide 4

Nuclear Reactions 01Nuclear Reactions 01

Animation

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/radioa7.swf

Chapter 22 Slide 5

Alpha Decay:Alpha Decay:

Chapter 22 Slide 6

Beta DecayBeta Decay

A beta particle Is an electron

emitted from the nucleus.

Forms when a neutron in the nucleus breaks down.1n 0e + 1P0 -1 1

Chapter 22 Slide 7

Write the nuclear equation for the beta decay of Co-60.

60Co 27

Learning CheckLearning Check

Chapter 22 Slide 8

Write the nuclear equation for the beta decay of Co-60.

60Co 60Ni + 0e 27 28 1

beta particle

SolutionSolution

Chapter 22 Slide 9

Positron Emission:Positron Emission:

Loss of a positron (a particle that has the same mass as but opposite charge than an electron)

e01

C116

B115 + e0

1

Chapter 22 Slide 10

• Gamma radiation is energy emitted from an unstable nucleus indicated by m.

• In a nuclear equation for gamma emission, the mass number and the atomic number are the same.

99mTc 99Tc + 43 43

Gamma RadiationGamma Radiation

Chapter 22 Slide 11

Electron Capture (K-Capture)Electron Capture (K-Capture)

Addition of an electron to a proton in the nucleusAs a result, a proton is transformed into a neutron.

p11 + e0

−1 n1

0

Chapter 22 Slide 12

• Alpha () Radiation: Are helium nuclei, that contain two protons and two neutrons.

• Alpha () emission reduces the mass number by 4 and the atomic number by 2.

242He


Chapter 22 Slide 13

Balancing Nuclear Equations

1. Conserve mass number (A).

The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants.

1n0U23592 + Cs138

55 Rb9637

1n0+ + 2

235 + 1 = 138 + 96 + 2x1

2. Conserve atomic number (Z) or nuclear charge.

The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants.

1n0U23592 + Cs138

55 Rb9637

1n0+ + 2

92 + 0 = 55 + 37 + 2x0

Chapter 22 Slide 14

212Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212Po.

4He242oralpha particle -

212Po 4He + AX84 2 Z

212 = 4 + A A = 208

84 = 2 + Z Z = 82

212Po 4He + 208Pb84 2 82

p11 + e0

−1 n1

0

Chapter 22 Slide 15

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/radioa7.swf

Chapter 22 Slide 16


• Write balanced equations for:

1. Alpha emission from curium-242

2. Beta emission from magnesium-28

3. Positron emission from xenon-118

4. Electron capture by polonium-204

• What particle is produced by decay of thorium-214 to radium-210?

Chapter 22 Slide 17

Radioactive Decay Rates 01Radioactive Decay Rates 01

Chapter 22 Slide 18

• Radioactive decay is kinetically a first-order process.

Decay Rate = k x N

The integrated form of the first-order rate law is:

lnNtN0

kt


N is number of radio active nuclei in the sample

ln[A]0

[A]

= k t

[A] = k1 . Nt

Chapter 22 Slide 19

Amount of Radioactive Material Remainig and half lifeAmount of Radioactive Material Remainig and half life

ln[A]0

[A]= k t

t½ln2k

= K ln2t1/2

=

ln[A]0

[A]= tln2

t1/2

)/(2lnln 1/20 ttN

N

t

[A]0 = k1 . N0

)/(2lnln 1/2

0tt

N

Nt

Radioactive Decay RatesRadioactive Decay Rates

Radioactive decay is a first-order process.

Chapter 22 Slide 21


• Half-Life: Radioactive decay is characterized by a half-life, t1/2, the time required for the number of radioactive nuclei in a sample to drop to half its initial value.

t12ln 2k

Chapter 22 Slide 22


Chapter 22 Slide 23

Chapter 22 Slide 24

Chapter 22 Slide 25

Chapter 22 Slide 26

lnNtN0

kt

How do you measure rate constant k ?

Chapter 22 Slide 27

Chapter 22 Slide 28

Chapter 22 Slide 29

Chapter 22 Slide 30

0.1813 /day

Chapter 22 Slide 31

Chapter 22 Slide 32

Chapter 22 Slide 33

Chapter 22 Slide 34

Chapter 22 Slide 35

Chapter 22 Slide 36

Chapter 22 Slide 37

Chapter 22 Slide 38

Chapter 22 Slide 39

Chapter 22 Slide 40

Chapter 22 Slide 41

Chapter 22 Slide 42

Chapter 22 Slide 43

Chapter 22 Slide 44

Carbon Dating 01Carbon Dating 01

Carbon-14 is produced in the upper atmosphere by

the bombardment of nitrogen atoms with neutrons:

Radioactive 14CO2 is produced, which mixes with

ordinary 12CO2 and is taken up by plants during

photosynthesis.

147

N + 10

n 146

C + 11

H

Chapter 22 Slide 45

Radiocarbon Dating

14N + 1n 14C + 1H7 160

14C 14N + 0 67 -1 t½ = 5730 years

Uranium-238 Dating

238U 206Pb + 8 4 + 6 092 -182 2 t½ = 4.51 x 109 years

Chapter 22 Slide 46


• During an organism’s life, 14CO2 and 12CO2 are in a dynamic equilibrium at a ratio of 1 part in 1012.

• When an organism dies, the 14C/12C ratio decreases as 14C undergoes decay to 14N.

• Measuring the 14C/12C ratio determines the age of the sample with a high degree of certainty.

• Ages of 1000–20,000 years are commonly determined. The half-life for 14C is 5730 years.

Chapter 22 Slide 47


• The carbon-14 decay rate of a sample obtained from

a young live tree is 0.260 disintegrations s–1 g–1. or

15.6 counts per minutes.

• Another sample prepared from an archaeological

excavation gives a decay rate of 0.186

disintegrations s–1 g–1.

• What is the age of the object?

)/(2lnln 1/2

0tt

N

Nt

Nuclear StabilityNuclear Stability

Chapter 22 Slide 49

Neutron-Proton RatiosNeutron-Proton Ratios

• Any element with more than one proton (i.e., anything but hydrogen) will have repulsions between the protons in the nucleus.

• A strong nuclear force helps keep the nucleus from flying apart.

• As the nuclei get heavier more neutron is needed to provide a stable nucleus.

Chapter 22 Slide 50


• Neutrons play a key role stabilizing the nucleus.

• Therefore, the ratio of neutrons to protons is an important factor.

Chapter 22 Slide 51


For smaller nuclei (Z 20) stable nuclei have a neutron-to-proton ratio close to 1:1.

Chapter 22 Slide 52


As nuclei get larger, it takes a greater number of neutrons to stabilize the nucleus.

Chapter 22 Slide 53

Stable NucleiStable Nuclei

The shaded region in the figure shows what nuclides would be stable, the so-called belt of stability.

Chapter 22 Slide 54

Stable NucleiStable Nuclei

• Nuclei above this belt have too many neutrons.

• They tend to decay by emitting beta particles.

1n 0e + 1P0 -1 1

Chapter 22 Slide 55

Stable NucleiStable Nuclei• Nuclei below the belt have

too many protons.• They tend to become more

stable by positron emission.

212Po 4He + 208Pb84 2 82

C116

B115 + e0

1

p11 + e0

−1 n1

0

Alpha emission

or electron capture:

Chapter 22 Slide 56

Nuclear Stability 05Nuclear Stability 05

• Radioactive products of a radioactive decay will undergo further disintegration.

• Some nuclei undergo a whole series of disintegrations called a decay series, leading to nonradioactive species.

Chapter 22 Slide 57

Binding energy 01Binding energy 01

• Since neutrons act as “glue” by overcoming proton–proton repulsions, the strength of these forces should be measurable.

• However, the activation energy required to force elementary particles close enough for reaction is very high and requires temperatures of about 107 K.

• Using Einstein’s equation ∆E = ∆mc2, we can attempt to calculate energies.

Chapter 22 Slide 58

Binding energy 02Binding energy 02

• Consider the formation of a helium-4 nucleus:Total theoretical mass of 2n + 2p = 4.031 88 amu

Observed mass of helium-4 nucleus = 4.001 50 amu

Mass difference = 0.030 38 amu

• Mass difference is called the mass defect of the nucleus. It results from combination of protons and neutrons. It is converted to energy during reaction and is a direct measure of nucleon binding energy.

Chapter 22 Slide 59

Energy Changes 03Energy Changes 03

• Using the Einstein equation, we can calculate the binding energy for a helium-4 nucleus:

• The mass defect = 0.030 38 amu = 0.030 38 g/mol = 3.038 x 10–5

kg/mol.

• ∆E = ∆mc2 = (3.038 x 10–5 kg/mol) (3.00 X 108 m/s)2 (1J/(1 Kg.m2/s2)

(1KJ/1000J)= 2.73 x 109 kJ/mol. (released energy)

(H2(g) + 1/2 O2 -> H2O (l), ΔH = -2.858 x 10-2 kJ/mol)

• The binding energy for helium-4 nucleus is 2.73 x 109 kJ/mol. Which means that 2.73 x 109 kJ/mol is released when helium-4 nucleus formed.

Mass loss of sun is 1010 Kg/sec, in 100 years it loses 6.6 PPT

Chapter 22 Slide 60

Energy Changes 04Energy Changes 04

• Binding Energies are usually expressed on a per–nucleon basis using the electron volt (eV) as the energy unit.

• 1 eV = 1.60 x 10–19 J and 1 MeV = 1.60 x 10–13 J.

• Helium-4 binding energy:

nMeV/nucleo 7.08 Energy binding 4He

nucleons 4

nucleus 1

J101.60

1MeV

nuclei/mol106.022

J/mol102.73Energy binding 4He

1323

12

Chapter 22 Slide 61

Chapter 22 Slide 62

Chapter 22 Slide 63

Chapter 22 Slide 64

Chapter 22 Slide 65

Chapter 22 Slide 66

(1J/(1 Kg.m2/s2)

Chapter 22 Slide 67

(1J/(1 Kg.m2/s2)

Chapter 22 Slide 68

(See slide 60)

Helium-6 is radioactive

Chapter 22 Slide 69

Chapter 22 Slide 70

Chapter 22 Slide 71

Chapter 22 Slide 72

Chapter 22 Slide 73

Chapter 22 Slide 74

Nuclear Fission and Fusion 01Nuclear Fission and Fusion 01

• Nuclear Fission is the fragmentation of heavy nuclei to form lighter, more stable ones.

Chapter 22 Slide 75


• Nuclear Fission is the fragmentation of heavy nuclei to form lighter, more stable ones.

• Neutrons released in the fission of 235U can induce three more fissions, then nine, and so on leading to a chain reaction.

• Critical mass is the mass required for the chain reaction to become self-sustaining.

Chapter 22 Slide 76

Chapter 22 Slide 77

Chapter 22 Slide 78

Chapter 22 Slide 79

Chapter 22 Slide 80

Chapter 22 Slide 81

Chapter 22 Slide 82

Chapter 22 Slide 83

• Fusion involves the combination of small nuclei to form a larger nucleus.

Nuclear FusionNuclear Fusion

Chapter 22 Slide 84

Nuclear FusionNuclear Fusion

Nuclear Fusion

Among the processes thought to occur in the Sun:

H1

2H1

1+ He2

3

H1

1 e1

0H1

1+ H1

2+

H1

1He2

3+ He2

4+ e1

0

He2

3 2He2

3+ He2

4+ H1

1

Chapter 22 Slide 85

Nuclear Fusion 04Nuclear Fusion 04

• Nuclear Fusion is the formation of heavier nuclei by the joining of lighter ones.

• Fusion products are generally not radioactive.

• Fusion requires high energies (temperatures over 107 K) to overcome the nuclear repulsions. The highest temperature obtained in The Large Hadron

Collider LHC (CERN) is 4X1012 • Fusion reactions are also called thermonuclear.http://www.pppl.gov/projects/pages/tftr.html

http://www.youtube.com/watch?v=6UioMaplabo

http://www.pppl.gov/projects/pages/tftr.html

Chapter 22 Slide 86

Chapter 22 Slide 87

Chapter 22 Slide 88


• Nuclear Reactors “control” the fission of 235U and use the energy produced to heat water that drives steam turbines.

Composition of the Spent FuelComposition of the Spent Fuel

• The spent nuclear fuel contains about 93% uranium (mostly U-238)

• about 1% plutonium • less than 1% minor actinides (neptunium, americium, and curium)

• 5% fission products

Global Nuclear WastesGlobal Nuclear Wastes

• Typical reactor will generate 20 to 30 tons of high-level nuclear waste annually

• The global volume of spent fuel is ,290,000 tons , and is

growing by approximately 10,000 tons annually.

• Despite billion of dollars of investment in various disposal options, the nuclear industry and governments have failed to come up with a feasible and sustainable solution.

U-238 decay chain (main branch)U-238 decay chain (main branch)

• Uranium-238 (half-life: 4.46 billion years) alpha decay ==>• Thorium-234 (half-life: 24.1 days) beta decay ==>• Protactinium-234m half-life: 1.17 minutes) beta decay ==>• Uranium-234 (half-life: 245,000 years) alpha decay ==>• Thorium-230 (half-life: 75,400 years) alpha decay ==>• Radium-226 (half-life: 1,600 years) alpha decay• ==>• Radon-222 (half-life: 3.82 days) ==> followed by radon

decay products (polonium, bismuth, lead isotopes)

Thorium-232Thorium-232

• Thorium-232 is, like U-238, has its own decay chain

• Dangerous decay products build up relatively quickly in Th-232

• They are thorium-228, actinium-228 (a beta-emitter), radium-228, and radium-224

• Radium-224 gives off radon-220 (which is similar to radon-222)

Repository capacityRepository capacity

• Three isotopes, which are linked through a decay process (Pu241, Am241, and Np237), are the major contributors to the estimated dose for releases from the repository, typically occurring between 100,000 and 1 million years, and also to the long-term heat generation that limits the amount of waste that can be placed in the repository

Composition of the Spent FuelComposition of the Spent Fuel

• The spent nuclear fuel contains about 93% uranium (mostly U-238)

• about 1% plutonium • less than 1% minor actinides (neptunium, americium, and curium)

• 5% fission products

Chapter 22 Slide 96

Nuclear Fission & POWERNuclear Fission & POWERNuclear Fission & POWERNuclear Fission & POWER

• Currently* about 103 Currently* about 103

nuclear power plants nuclear power plants

in the U.S. and about in the U.S. and about

442 worldwide.442 worldwide. There

65 currently under

construction

• 17% of the world’s energy 17% of the world’s energy

comes from nuclear.comes from nuclear.

* 12-03-12

Nuclear Fission and FusionNuclear Fission and Fusion

Chapter 22 Slide 98Size of a fission bumbSize of a fission bumb


Courtesy US Department of Energy

Chapter 22 Slide 99


The plutonium was produced in Hanford Nuclear reservation

Chapter 22 Slide 100

Nuclear Transmutation 01Nuclear Transmutation 01

• Nuclear Transmutation

is the change of one element

into another.

• Achieved by bombarding

atoms with high-energy

particles in a

particle accelerator.

• Transmutation can synthesize

new elements.

http://www.youtube.com/watch?v=sxAxV7g3yf8

http://www.youtube.com/watch?v=sxAxV7g3yf8


Nuclear Transmutation 02Nuclear Transmutation 02

• Cyclotrons consist of D-shaped electrodes (dees) with a large, circular magnet above and below the vacuum chamber.

• Particles are accelerated by making the dees alternatively positive and negative.

• When the particles are moving at sufficient velocity they are allowed to escape the cyclotron and strike the target.


Nuclear TransmutationNuclear Transmutation

Elements beyond 92 Elements beyond 92 (transuranium)(transuranium) made made

starting with an starting with an n,n, reaction reaction

2382389292U + U + 11

00n ---> n ---> 2392399292U + U +

2392399292U U ---> ---> 239239

9393Np + Np + 00-1-1

2392399393Np Np ---> ---> 239239

9494Pu + Pu + 00-1-1



Nuclear Transmutation: The change of one element into another.

Plutonium-241 can be made by bombarding uranium-238 with alpha particles:

Pu94

241 Am95

241+ e-1

0

Plutonium-241 decays into americium-241:

He2

4U92

238+ Pu94

241+ n0

1



Nuclear Transmutation: The change of one element into another.

Cobalt-60 is used in radiation therapy for cancer patients. The overall preparation process can be written as:

2Fe26

58+ Co27

60+ e-1

0n0

1


Radioisotopes in Medicine• 1 out of every 3 hospital patients will undergo a nuclear

medicine procedure

• 24Na, t½ = 14.8 hr, emitter, blood-flow tracer

• 131I, t½ = 14.8 hr, emitter, thyroid gland activity

• 123I, t½ = 13.3 hr, ray emitter, brain imaging

• 18F, t½ = 1.8 hr, emitter, positron emission tomography

• 99mTc, t½ = 6 hr, ray emitter, imaging agent

Brain images with 123I-labeled compound


Detecting Radioactivity 01Detecting Radioactivity 01

• Matter is ionized by radiation.

• We can detect radiation by measuring its ionizing properties.

• Ionizing radiation includes particles, particles, rays, X rays, and cosmic rays.

• ray & X rays are high-energy photons ( = 10–8 to 10–11 m). Cosmic rays originate in interstellar space.



• A Geiger counter determines the amount of ionization by detecting an electric current.

• A thin window is penetrated by the radiation and causes the ionization of Ar gas.

• The ionized gas carried a charge and so current is produced.

• The current pulse generated when the radiation enters is amplified and counted.



• Scintillation counters use a substance called phosphor (sodium iodide & thallium iodide), which emits a flash of light when struck by radiation.

• Flashes can be counted electronically and converted to an electric signal.


• Radiotracers (radio-labels) are used to follow an element through a chemical reaction.

• Photosynthesis has been studied using 14C-containing carbon dioxide:

• The carbon dioxide is said to be 14C-labeled.

614CO2 + 6H2O 14C6H12O6 + 6O2sunlightchlorophyll

Application of Radioisotopes05Application of Radioisotopes05


Biological Effects of Radiation 01Biological Effects of Radiation 01

• The penetrating power of radiation is a function of its mass: -rays > -particles >> -particles.

• When ionizing radiation passes through tissue it removes an electron from water to form H2O+ ions.

• The H2O+ ions react with another water molecule to produce H3O+ and a highly reactive •OH radical.

• Free radicals generally undergo chain reactions, producing many radicals in the biomolecules.



• -rays are particularly harmful

because they penetrate in the

same way as X rays.

• -particles interact with the skin

and -particles interact up to 1

cm into the tissue

• -particles are particularly

dangerous when ingested or

inhaled.


Radiation MeasurementRadiation Measurement

• The Curie measures the number of atoms that decay in one second. Curie: 1 Ci = 3.7 x 10Curie: 1 Ci = 3.7 x 101010 distintegrations/sdistintegrations/s

• The rad* (radiation absorbed dose) measures the radiation absorbed by the tissues of the body.

• The rem (Roentgen equivalent for man (rem) ) measures the biological damage.

*1 Rad = 2.58 x 10-4 Coulombs /kg air. The exposure rate expresses the rate of charge production per unit mass of air and

is commonly expressed in roentgens per hour (R/h) or milliroentgens per hour (mR/h).


Biological Effects of RadiationRadiation absorbed dose (rad)

1 rad = 1 x 10-5 J/g of material

Roentgen equivalent for man (rem)

1 rem = 1 rad x Q Quality Factor-ray = 1

= 1 = 20

Curie: 1 Ci = 3.7 x 10Curie: 1 Ci = 3.7 x 101010

distintegrations/sdistintegrations/s

SI unit is the becquerel: SI unit is the becquerel:

Bq = 1 Bq = 1 distintegrations/sdistintegrations/s


Units of Radiation MeasurementUnits of Radiation Measurement


Background RadiationBackground Radiation

• A person is exposed to radiation from naturally occurring radioisotopes and medical X rays.


Biological Effects of RadiationBiological Effects of Radiation


Applications of Nuclear ChemistryApplications of Nuclear Chemistry

The half-life of carbon-14 is 5730 years:

The measured ratio of carbon-14/carbon-12 after death can determine how long ago the organism died.

Dating with Radioisotopes

e-1

0C14

14 N7

14+


Applications of Nuclear ChemistryApplications of Nuclear Chemistry

Geologic age can be determined by analysis of potassium-40:

Dating with Radioisotopes

e1

0K19

40 Ar18

40+

e-1

0K19

40 Ar18

40+

Potassium-40 has a half life of 1.25 billion years. Mass Spectroscopy is used to measure Ar-40 in a sample of molten rock to calculate the age of the rock.

Bone scan Using Radiactive Technetiun-99

Bone scan

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