luminescent materials for dosimetricapplicationsluminescent materials for dosimetricapplications...
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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
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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?
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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 (%)
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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
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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
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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
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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+
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LuminescenceLuminescence efficiencyefficiency
How efficiently transform TL/OSL materials absorbed energy into light?
i
energy emitted
energy absorbedη =
photonsN h
mD
ν=
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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%
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• 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
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• 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?
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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
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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
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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
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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
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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