Scintillator materials for gamma ray spectroscopy cherepy forexternal
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Transcript of Scintillator materials for gamma ray spectroscopy cherepy forexternal
Lawrence Livermore National Laboratory
N.J. Cherepy, [email protected]. Payne, B.W. Sturm, J.D. Kuntz, Z.M. Seeley, B.L. Rupert, R.D. Sanner,
T.A. Hurst, P. Thelin, S.E. Fisher, O.B. Drury
Lawrence Livermore National Laboratory, Livermore, CA 94550
K.S. Shah and team, Radiation Monitoring Devices
A. Burger and team, Fisk University
L.A. Boatner and team, Oak Ridge National Laboratory
Scintillator Materials for
Gamma Ray Spectroscopy February 2011
LLNL-PRES-468519
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344
Funded by DHS/DNDO
and DOE NA-22
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Lawrence Livermore National Laboratory
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N. CHEREPY [email protected]. CHEREPY [email protected]
Requirements for new detector materials:1) High energy resolution and stopping — to discriminate gamma spectra
2) Low cost / maintenance — starting materials; growth / ruggedness
3) No intrinsic radioactivity or toxic constituents
Overview
Our Directed Search Method
has been used to discover:• Single Crystals SrI2(Eu)
• Transparent Ceramics Garnet(Ce)
• Plastics Bi-loaded Polymer
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N. CHEREPY [email protected]. CHEREPY [email protected]
For radioisotope identification, gamma scintillators with
high resolution, low cost and large volume are needed
High resolution enabled by:-High Light Yield
-Low Non-Proportionality
-Uniform Material Response
-Optimized Light Collection
-Accurate Readout
CURRENT FUTURE
Gamma
Scintillation
Detectors
Goals:
• 2% resolution
• Room temperature
• 2000 cm3
• $10/cm3
• No self-activity
NaI(Tl)
• 6% resolution
• Room temperature
• 2000 cm3
• $10/cm3
LaX3(Ce)
• 3% resolution
• Room temperature
• 400 cm3
• $100/cm3
• Self-activity
P. Dorenbos
SrI2:EuGYGAG:Ce
Bi-loaded plastic
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Single crystals Ceramics Plastics
Often hygroscopic/air-sensitive
Fragile/brittle
Complex to grow large crystals
Can have gradients & non-
uniformity
Unreactive with air, water
Mechanically durable
Large sizes (100 cm3 Nd:YAG
ceramics commercially available)
Increased activator uniformity
Can form high melting point
oxides
Unreactive with air, water
Mechanically durable
Large sizes, low cost
All crystal structures possible
Best energy resolution
materials- LaBr3(Ce), SrI2(Eu)
~2.6% @ 662 keV
Requires cubic material
Good energy resolution-
GYGAG(Ce) Gadolinium Garnet
~4.5% @ 662 keV w/PMT
Non-standard polymer required
Bi-loading uniformity important
Energy resolution so far ~7% @
662 keV
Inorganic single crystal and ceramic scintillators are being
developed for gamma ray spectroscopy
2 inch
SrI2(Eu)
Bi-loaded polymers,
1 cm3
GYGAG(Ce), 1 in3
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N. CHEREPY [email protected]. CHEREPY [email protected]
For gamma ray spectroscopy, SrI2(Eu) comparable to LaBr3(Ce) and
GYGAG(Ce) is better than NaI(Tl)
300
200
100
0
cou
nts
800600400200
Energy (keV)
NaI(Tl) GYGAG(Ce) LaBr3(Ce)
SrI2(Eu)
Cs-137
101
102
103
104
co
un
ts
400300200100
Energy (keV)
NaI(Tl) GYGAG(Ce) LaBr3(Ce)
SrI2(Eu)
Ba-1336000
5000
4000
3000
2000
1000
0
Co
un
ts
6040200
Energy (keV)
9.8% Am-241
7.7%
NaI(Tl) LaBr3(Ce)
SrI2(Eu)
x-rays
12.4%
Co
un
tsC
ou
nts
2500
2000
1500
1000
500
0C
ou
nts
14001300120011001000900
Energy (keV)
NaI(Tl) GYGAG(Ce) LaBr3(Ce)
SrI2(Eu)
6.4%
6.1%
2.0% 1.9%
Co-60
3.3%3.5%
SrI2(Eu) crystals grown at RMD, Inc.
Cut, polished and encapsulated by LLNL
20
16
12
8
4
0En
erg
y R
eso
lutio
n (
%)
3 4 5 6 7 8 9
1002 3 4 5 6 7 8 9
1000Energy (keV)
NaI(Tl) GYGAG(Ce) LaBr3(Ce)
SrI2(Eu)
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Comparison of gamma spectra at 662 keV for ~(1”)3 scintillators
reveals effects of resolution and photopeak efficiency, SPP
LaBr3(Ce),
f1.8x2 cm
R=3%
GYGAG(Ce),
f1.1”x0.24”
R=4.7%
• For comparison, 1”x1” Ge photopeak efficiency, SPP = 3.9%
• SPP defined as fraction of gammas intercepting detector that lead to photopeak
SrI2(Eu),
f1”x1”
R=3%
Scintillator SPP (662kev)
for 1”x1” (%)
LaBr3(Ce) 11.1
SrI2(Eu) 11.4
CLYC(Ce) 5.3
NaI(Tl) 8.5
GYGAG(Ce) 12.8
CLYC(Ce),
f1”x1”
R=4.3%
NaI(Tl),
f1”x1”
R=5.8%
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300
250
200
150
100
50
0
co
un
ts
700600500400300200100
Energy (keV)
2.9% at 662 keV
1 in3
encapsulated crystal
Production of encapsulated SrI2(Eu) underway
Property LaBr3(Ce) SrI2(Eu) Comparison
Melting Point 783 ºC 538 ºC Less thermal stress
Handling Easily cleaves Resists cracking Better processing
Light Yield 60,000 Ph/MeV 90,000 Ph/MeV Higher
Proportionality contribution ~2.0% ~2.0% Favorable
Inhomogeniety 0% >1% (current) Impurities and surfaces being addressed
Decay time 30 nsec 0.5-1.5 msec Fast enough to avoid deleterious signal pile-up
Self-radioactivity La ~ 3x NORM None Less noise
Hygroscopic / air sensitive? Very Very Similar
absorption (2x3”, 662 keV) 22% 24% Similar
1.15
1.10
1.05
1.00
0.95
0.90
Re
lative L
igh
t Y
ield
3 4 5 6 7
102 3 4 5 6 7
1002 3 4 5 6 7
1000Electron Energy (keV)
RMD SrI2(0.5%Eu)
ORNL SrI2(4%Eu)
ORNL SrI2(6%Eu)
Encapsulated RMD SrI2(3%Eu)
NaI(Tl) LaBr3(Ce)
SrI2(Eu): excellent LY
proportionality
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We have been working to identify an optimal Gd-based
garnet scintillator for the past five years
2006-7 2007-8 2008-9
Composition GAG GYAG GGG GSAG GYSAG GGAG GYGAG
Phase Stability Poor Moderate Excellent Excellent Excellent Moderate Excellent
-LY(Ph/MeV) ___ 40,000 ___ 25,000 30,000 55,000 50,000
En. Res. (662 keV) ___ 11% ___ 11% 10% 9% 4-5%
Current status:
1 in3 parts formed routinely
To optimize performance:
Photodetector matched to green scintillation
2010-11
Scale-up of GYGAG(Ce)
1 in3
5000
4000
3000
2000
1000
0
Co
un
ts
4003002001000
Channel
GYGAG(Ce) ceramic:
4.5% at 662 keV w/ PMT
0 200 400 600
0
500
1000
1500
0.5% 3.9%
Xc = 417
Count
s
MCA Channel
GYGAG_APD_1710V_-23C_6us
GYGAG(Ce) ceramic:
3.9% at 662 keV w/ RMD APD
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Lawrence Livermore National Laboratory
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Recently we have developed polymer scintillators
offering energy resolution approaching that of NaI(Tl)
• Non-standard polymer that is
formable by methods similar to
standard plastic scintillator
• Bi organometallic, 40 wt%
• Current size F1.9x0.17 cm3
• Escape peak in small scintillator
eliminated when larger
3
2
1
0
rel. c
ou
nts
6004002000
Energy (keV)
Photopeak662 keV
FWHM = 6.8%simulated 3" x 3"
3
2
1
0
rel. c
ou
nts
Photopeak662 keV
FWHM = 9%
Backscatter escape
BackscatterCompton
edgeEscape 687 keV
A
B
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Materials for future gamma spectrometers?
Gamma Spectroscopy Scintillator Zeff Light Yld
(Ph/MeV)
En Res,
662 keV
Nonprop
En Res,
662 keV
SPP,
662 keV,
(1 in3)
Single
crystals
NaI(Tl) 50 40,000 7% 5.0% 8.5%
LaBr3(Ce) 44 63,000 3% 2.2% 11.1%
SrI2(Eu) 49 90,000 3% 2.2% 11.4%
Garnet
ceramics
(Gd,Y)3(Al,Ga)5O12(Ce) 47 50,000 4.5% 1.9% 12.8%
Plastics
Standard PVT 4.5 15,000 8% (Compton)
3.5% 0
LLNL Bi-loaded polymers 26 10,000-
30,000
7% 3.5% 1.5%