Challenge the future

DelftUniversity ofTechnology

Luminescent materials for dosimetric applications

Adrie J.J. Bos

Delft University of Technology, The Netherlands

2

Basic assumption: There is a relation between:

• light yield

and

• absorbed dose

3

γ, X-rays, e-, p, HCP

ionisation storageheat

λemission

Steps in TL DosimetrySteps in TL Dosimetry

Luminescent material

1. Irradiation

2. Storage

3. Read-out

4

Ionisation Storage Read-out

λstimulation λemission>

laserlaser

Steps in OSL DosimetrySteps in OSL Dosimetry

Luminescent material

γ, X-rays, e-, p, HCP

Q1: How is it energytically possible that Eem > Estim?

5

Which luminescent material is a good Which luminescent material is a good

dosimetricdosimetric material?material?

• Application area• Type of radiation• Type of dosimetry

6

Application areasApplication areas

• Personnel dosimetry• Extremity• Whole body

• Environmental dosimetry• Terrestrial• Space

• Medical dosimetry• Radiotherapy • Diagnostic radiology• Nuclear medicine

• High dose dosimetry• Radiation processing• Nuclear reactors

7

Type of radiationType of radiation

• Low LET radiation• photons• betas• electrons

• High LET radiation• protons• Heavy Charged Particles (HCP)• neutrons

• UV radiation

8

Type of DosimetryType of Dosimetry

• Passive

• Thermoluminescence Dosimetry (TLD)

• Optically Stimulated Luminescence Dosimetry (OSLD)

• Electron Paramagnetic Resonance (EPR)

• Film Dosimetry

• Active

• Fiber optic dosimetry

Source: Akselrod, et al. Radiat. Meas.

41(2007)S78

9

• Sensitivity

• Linearity

• Appropriate energy dependence

• independence radiation energy

• tissue equivalent

• Long term stability

• Reproducible

• Easy to re-set, low residual

General requirementsGeneral requirements

10

• Match luminescence spectrum with maximum sensitivity of PM tube

• Mechanically strong

• Chemically inert

• No effect of day light (for TL)

• Radiation resistant

• Batch homogeneity

• Simple reuse

• Low production price

Specific requirementsSpecific requirements

11

Application areasApplication areas

• Personnel dosimetry 10-5 – 0.5• Extremity• Whole body

• Environmental dosimetry 10-7 – 10-2

• Terrestrial• Space

• Medical dosimetry• Radiotherapy 10-1 – 100• Diagnostic radiology 10-6 - 10-1

• Nuclear medicine

• High dose dosimetry• Radiation processing 101 - 106

• Nuclear reactors 103 - 109

Dose range (Gy)

12

Application areasApplication areas

• Personnel dosimetry 10-5 – 0.5 -30, +50• Extremity• Whole body

• Environmental dosimetry 10-7 – 10-2 ±30• Terrestrial• Space

• Medical dosimetry• Radiotherapy 10-1 – 100 ?• Diagnostic radiology 10-6 - 10-1

• Nuclear medicine

• High dose dosimetry 15• Radiation processing 101 - 106

• Nuclear reactors 103 - 109

Dose range (Gy)

Uncertainty1SD (%)

Q2: Which uncertainty is required in radiotherapy?

13

Application areasApplication areas

• Personnel dosimetry 10-5 – 0.5 -30, +50• Extremity• Whole body

• Environmental dosimetry 10-7 – 10-2 ±30• Terrestrial• Space

• Medical dosimetry• Radiotherapy 10-1 – 100 3.5• Diagnostic radiology 10-6 - 10-1

• Nuclear medicine

• High dose dosimetry 15• Radiation processing 101 - 106

• Nuclear reactors 103 - 109

Dose range (Gy)

Uncertainty1SD (%)

14

Application areasApplication areas

• Personnel dosimetry 10-5 – 0.5 -30, +50 +• Extremity• Whole body

• Environmental dosimetry 10-7 – 10-2 ±30 ++• Terrestrial• Space

• Medical dosimetry• Radiotherapy 10-1 – 100 3.5 +• Diagnostic radiology 10-6 - 10-1 3.5 +• Nuclear medicine

• High dose dosimetry 15 -• Radiation processing 101 - 106

• Nuclear reactors 103 - 109

Dose range (Gy)

Uncertaint1SD (%) Fading

15

Application areasApplication areas

• Personnel dosimetry 10-5 – 0.5 -30, +50 + +• Extremity• Whole body

• Environmental dosimetry 10-7 – 10-2 ±30 ++ ±• Terrestrial• Space

• Medical dosimetry• Radiotherapy 10-1 – 100 3.5 + ++• Diagnostic radiology 10-6 - 10-1 3.5 + +• Nuclear medicine

• High dose dosimetry 15 - - -• Radiation processing 101 - 106

• Nuclear reactors 103 - 109

Dose range (Gy)

Uncertainty 1 SD (%) Fading TE

16

From (1) and (2):

tissueen

TLen

tissue

TL

D

D

)/(

)/(

ρµρµ=

)1()/( TLenTL ED ρµΦ=

( / ) (2)tissue en tissueD E µ ρ= Φ

Tissue equivalence for Photons Tissue equivalence for Photons

16.9CaF2

7.32Li2B4O7

7.21BeO

7.51Water

7.77Air

8.31LiF

7.35Soft tissue

ZeffMaterial

17

Tissue equivalence for neutronsTissue equivalence for neutrons

( / )trD K E µ ρ≈ =Φ

10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 7

Neutron energy (eV)

10 -7

10 -6

10 -5

10 -4

10 -3

10 -2

10 -1

10 0

10 1

Ker

ma

coef

ficie

nt (

pGy

cm2)

tissue

tissue

N

C

O

O

C

H

N

H

H (0,101)

C (0,111)

N (0,026)

O (0,762)

mass

fraction( / )tr

KE µ ρ=

Φ

(NH4)2BeF4:Tl+

(NH4)2SiF6:Tl+

18

LuminescenceLuminescence efficiencyefficiency

How efficiently transform TL/OSL materials absorbed energy into light?

i

energy emitted

energy absorbedη =

photonsN h

mD

ν=

19

Type of luminescence Induced by Application Efficiency (%) Black body radiation Photoluminescence Cathodoluminescence Electroluminescence Thermoluminescence

Heat Photons Electrons Electric field Ionising radiation

Tungsten filament lamp Fluorescent lamp Television screen LED, flat panel display Dosimetry, Dating

∼5% ∼20% ∼10% 0.1-50%

LuminescenceLuminescence phenomenaphenomena, , applicationsapplications

and and typicaltypical efficienciesefficiencies

Q3: ηTLD-100 ?

A: 0.01%

B: 0.10%

C: 1.0%

D: 10%

20

• creation of electron-hole pairs (neh∼ Eγ/Weh=hν/βEg)

• thermalisation and trapping (ηtr)

• release of charge carriers from the trap (p)

• transfer to luminescent centre (S)

• de-excitation of the Luminescent Centre (Q)

• escape from the sample (ηesc)

Steps in the energy conversion process

i tr escg

hpSQ

E

νη η ηβ

=

ηesc

Valence band

Cond. band

S

Q

p

Eg

ηtr

21

LuminescenceLuminescence efficiencyefficiency

Suppose: ηtr = 1, p = 1, S = 1, Q = 1, ηesc = 1

i tr escg

hpSQ

E

νη η ηβ

=

,maxig

h

E

νηβ

=

Valence band

Cond. band

S

Q

p

Eg

ηtr

22

ηηi,maxi,max and and ηηexpexp for some TL materialsfor some TL materials

Eg hν ηi,max ηexp TL material eV β nm eV % % LiF:Mg,Ti 13.6 1.7 410 3.02 13 0.032 – 0.039 LiF:Mg,Cu,P 0.91

CaF2:Dy(TLD-200) 12.6 1.8 480 2.58 11 4.1

CaF2:Cu,Ho 12.6 1.8 390 3.18 14

CaF2:Tm 0.29

CaF2:Mn 0.44

KMgF3:Ce 12.6 2 360 3.44 14

BeO 10.6 2 335 3.70 17 CaSO4:Dy 9.5 2 575 2.16 11 CaSO4:Mn 1.2

Al2O3:C 8.7 2.7 420 2.95 13 0.84

Li2B4O7:Mn 8.5 2 620 2.00 12 0.3 C (diamond) 5.5 2.9 498 2.49 16

Average ∼13 ∼1

23

• creation e-h pairs ~13%

• trapping (ηtr): ?

• release of charge carriers from the trap (p) ++

• transfer to luminescent centre (S) - +

• de-excitation of the Luminescent Centre (Q) - +

• escape from the sample (ηesc) +

Efficiency various stepsEfficiency various steps

Conclusion:

the trapping efficiency plays a dominant role in the overall effciency

24

Well known TL/OSL materialsWell known TL/OSL materials

• LiF family

• CaSO4:RE (RE= Dy, Tm, Sm)

• CaF2:Mn

• Li2B4O7:Mn

• MgB4O7:Dy,Na

• Al2O3:C

• BeO

•

•

• Al2O3:C• BeO• SrS:Ce,Sm••

Q4: Which class of materials do not show TL?

25

LiFLiF familyfamily

• LiF: Mg,Ti

•Patent 1963

•Thermo Electron (TLD-100,TLD-600, TLD-700)

•TLD Poland: LiF:MT

• LiF: Mg,Cu,P

• First mentioned by Nakajima et al. 1978

• SSDL, Beijng, Cina: GR200

• Nemoto, Japan, NTL-500

• Thermo Electron: TLD100H

• TLD Poland: LiF:MCP

26

Glow curves Glow curves LiFLiF

Source: Bilski., Radiat. Prot. Dosim. 100(2002)199

LiF:Mg,Cu,P

LiF:Mg,Ti

27

Dose responseDose response

Source: P. Olko, in: Y.S. Horowitz: Microdosimetricresponse … (Elsevier, Amsterdam, 2006)

0

0

( ) ( )( )

TL D TL Df D

D D=

Linear: f(D) = 1

supralinear: f(D) >1

sublinear: f(D) < 1

28

Role of Role of dopantsdopants

LiF:Mg,Ti LiF:Mg,Cu.P

Mg: 0.01 – 0.02% Mg: 0.2%

Ti: 10 – 15 ppm P: 1 – 4%

Cu: 0.02 -0.5%

Anneal procedure

1 h 400 °C 10 min @240 °C

24 h 80 °C

29

TLD TLD cyclecycle

30

GlowGlow curve TLDcurve TLD--100 100 afterafter storagestorage

31

Requirements OSL materialRequirements OSL material

• Sensitivity

• Trapping centres:

i) Thermally stable

ii) Optically accessible

• Good separation between emission and stimulation bands

• Dose erasure by optically bleaching

32

OSL reader (schematic)OSL reader (schematic)

1 mW laser: 1017 photons cm-2 s-1

OSL-signal: < 106 photons cm-2 s-1

Q5: What is the role of the colour filter?

33

AlAl22OO33:C:C

• before 1990: Al2O3 known as TL material

• 1990: anion-deficient Al2O3:C developed as high sensitive TL material

• 1995: OSL material

• Application in

• Personnel dosimetry

• Environmental dosimetry

• Retrospectrive dosimetry

• Dating applications (equivalent to quartz)

Q6: What is the role of C?

A: Trapping centre

B: Luminescent centre

C: None of both

34

Emission and stimulation spectra of AlEmission and stimulation spectra of Al22OO33:C:C

Source: Botter-Jensen et al. Radiat. Meas. 22 (1997) 715.

350 400 450 500 550 600 650 7000

100

200

300

Em

issi

on in

tens

ity (

a.u.

)

Emission wavelength (nm)

e- + F+ → F* → F + hν420 nm

35

OSLOSL--signal of signal of Al2O3:CAl2O3:C

0 10 20 30 40 50

Tijd (s)

10|2

10|3

10|4

10|5

stimulatie = 470 nm

0 mGy

1

24

7

15

30 mGy

Time (s)

λstimulation = 470 nmO

SL s

ignal (a

.u)

36

Dose responseDose response

Source: Akselrod and McKeever, Radiat. Protec. Dosim. 81 (1999) 167

Kodak XV-2 film

120 kVp

280 kVp 60Co

6MV photons

20 MeV electron

Source:

Mota, et al. Phys. Med. Biol. 35 (1990) 565

37

Environmental dosimetry

Source: Bøtter-Jensen et al. Radiat. Meas. 27 (1997) 295-298

38

BeOBeO

• Known for a long time as TL material

(used in routine personnel dosimetry by the ENEA-Italy dosimetry service)

• Relatively low TL sensitivity

• Strong TL self-absorption

• Strong supralinearity

• Highly tissue equivalent;

Zeff(BeO) = 7.2 ; Zeff(tissue) = 7.4

• Rediscovered as OSL material (Bulur, Sommer et al.)

39

BeOBeO: OSL dose response: OSL dose response

0 50 100 150 200 250 300 350 400 450 500

102

103

104

105

106

1 mGy 2 mGy 4 mGy 8 mGy 16 mGy 32 mGy 64 mGy 128 mGy 256 mGy

OS

L si

gnal

(co

unts

/cha

nnel

)

Time (s)

BeO Batch 5

1 10 100

106

107

108

BeO batch 5

Inte

grat

ed lu

min

esce

nce

(cou

nts)

Dose (mGy)

OSL (9 - 509 s)

40

BeOBeO: dose response: dose response

1 10 100104

105

106

107

108BeO batch 5

Inte

grat

ed lu

min

esce

nce

(cou

nts)

Dose (mGy)

TL (130 - 360 °C) OSL (9 - 509 s)

0.1 1 10 100 1000102

103

104

105

106

107

108

Inte

grat

ed L

umin

esce

nce

(cou

nts)

Dose (Gy)

Batch 5 (OSL: 0 - 250 s) Batch 5 (TL: 100-300 °C)

41

CuCu++ doped fused quartzdoped fused quartz

Source: Justus et al Radiat. Protec. Dosim. 81(1999)5

λstimulation= 790 nm

X = 2 R

42

MgO:TbMgO:Tb3+3+

1 2 3 4 5 6 7 8 9 10

101

102

103

104

0 mGy 1 mGy 2 mGy 4 mGy 8 mGy 16 mGy 32 mGy 64 mGy 128 mGy 256 mGy 512 mGy 10 24 mGy 2048 mGy 4096 mGy 8192 mGy

OSL from a "Single Grain"

OS

L si

gnal

(ar

b. u

nits

)

Time (s)

100 101 102 103 104

101

102

103

104

105

Inte

grat

ed O

SL

sign

alDose (mGy)

λstimulation= 470 nm

Irradiation: 90Y/90Sr

43

MgO:TbMgO:Tb3+ 3+ : Fading : Fading

0 50 100 150 200 250 300 350 400 450

1

3

2

Temperature (°C)

-5 0 5 10 15 20 25 30 35 400

10

20

30

40

50

60

70

80

90

100

Time (h)

Nor

mal

ised

sig

nal

OSL TL peak 1+2 TL peak 3

44

SrS:Ce,SmSrS:Ce,Sm

Source: Lapraz te al. Phys. Stat. Sol. (a) 203 (2006) 3793

λstimulation= 1.04 µm

Irradiation: UV (350 nm)

45

SrS:Ce,SmSrS:Ce,Sm comparison with Alcomparison with Al22OO33:C:C

• Emission and stimulation bands are well separated

• No deep traps, SrS is fully reset after reading

• Strong fading

Source: Lapraz et al. Phys. Stat. Sol. (a) 203 (2006) 3793

Benoit et al. University of Montpellier, France

a = TL signal; b = OSL signal

46

Attractive features:

• Tissue equivalent

• Chemical inertness

• Radiation hardness

• Physically robust

• Safe for in vivo use

Chemical Vapor Deposition (CVD) DiamondChemical Vapor Deposition (CVD) Diamond

47

Chemical Chemical VapourVapour Deposition DiamondDeposition Diamond

Source: Goncalves et al Optical Materials 27(2005)1231

B doped B doped

48

Problems with CVD DiamondProblems with CVD Diamond

• Fading of the TL signal

• Sensitivity to daylight

• Poor linearity

• Poor reproducibility

49

Concluding remarks

• The development of new dosimetric materials goes slowly

• The market is dominated by LiF and Al2O3

• Even of well-known dosimetric materials the exact mechanism is unknown

• The key issue in developing an improved dosimetric material is

a high concentration of stable trapping centres

that can be synthesized in a reproducible way