This document discusses scintillator materials for gamma ray spectroscopy. It describes Lawrence Livermore National Laboratory's efforts to develop new scintillator materials with high energy resolution and stopping power to discriminate gamma ray spectra, while being low cost and having no intrinsic radioactivity. Some promising new materials discussed include single crystal strontium iodide doped with europium, ceramic gadolinium gallium aluminum garnet doped with cerium, and bismuth-loaded polymer plastics. These new materials show energy resolutions that improve on existing sodium iodide and offer potential for lower cost gamma spectroscopy detectors.

1. Lawrence Livermore National Laboratory
Scintillator Materials for
Gamma Ray Spectroscopy
February 2011
Funded by DHS/DNDO
and DOE NA-22
N.J. Cherepy, cherepy1@llnl.gov
S.A. 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 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

2. Official Use Only
Overview
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
Our Directed Search Method
has been used to discover:
• Single Crystals  SrI2(Eu)
• Transparent Ceramics  Garnet(Ce)
• Plastics  Bi-loaded Polymer
Lawrence Livermore National Laboratory
N. CHEREPY cherepy1@llnl.gov 2

3. For radioisotope identification, gamma scintillators with
Official Use Only
high resolution, low cost and large volume are needed
NaI(Tl)
• 6% resolution
CURRENT • Room temperature FUTURE
• 2000 cm3
Gamma • $10/cm3 Goals:
Scintillation • 2% resolution
LaX3(Ce) • Room temperature
Detectors • 3% resolution • 2000 cm3
• Room temperature • $10/cm3
• 400 cm3 • No self-activity
• $100/cm3
• Self-activity
Bi-loaded plastic
P. Dorenbos High resolution enabled by:
-High Light Yield
-Low Non-Proportionality
-Uniform Material Response
-Optimized Light Collection
GYGAG:Ce SrI2:Eu
-Accurate Readout
Lawrence Livermore National Laboratory
N. CHEREPY cherepy1@llnl.gov 3

4. Inorganic single crystal and ceramic Only
Official Use
scintillators are being
developed for gamma ray spectroscopy
Single crystals Ceramics Plastics
SrI2(Eu) GYGAG(Ce), 1 in3
2 inch
Bi-loaded polymers,
1 cm3
 Often hygroscopic/air-sensitive  Unreactive with air, water  Unreactive with air, water
 Fragile/brittle  Mechanically durable  Mechanically durable
 Complex to grow large crystals  Large sizes (100 cm3 Nd:YAG  Large sizes, low cost
 Can have gradients & non- ceramics commercially available)
uniformity  Increased activator uniformity
 Can form high melting point
oxides
 All crystal structures possible  Requires cubic material  Non-standard polymer required
 Best energy resolution  Good energy resolution-  Bi-loading uniformity important
materials- LaBr3(Ce), SrI2(Eu) GYGAG(Ce) Gadolinium Garnet  Energy resolution so far ~7% @
~2.6% @ 662 keV ~4.5% @ 662 keV w/PMT 662 keV
Lawrence Livermore National Laboratory
N. CHEREPY cherepy1@llnl.gov 4

5. Official Use Only
For gamma ray spectroscopy, SrI2(Eu) comparable to LaBr3(Ce) and
GYGAG(Ce) is better than NaI(Tl)
4
6000 10
9.8% NaI(Tl) Ba-133
Am-241 GYGAG(Ce)
5000 NaI(Tl)
LaBr3(Ce) 3 LaBr3(Ce)
4000 10
Counts
counts
Counts
SrI2(Eu) 12.4% SrI2(Eu)
3000
2
2000 x-rays 10
1000
7.7%
0 10
1
0 20 40 60 100 200 300 400
Energy (keV) Energy (keV)
2500
NaI(Tl) Cs-137 NaI(Tl) 6.4% Co-60
300
GYGAG(Ce) 2000 GYGAG(Ce)
LaBr3(Ce) LaBr3(Ce)
Counts
6.1%
Counts
counts
200 SrI2(Eu) 1500 SrI2(Eu) 3.5% 3.3%
1000
100
500
2.0% 1.9%
0 0
200 400 600 800 900 1000 1100 1200 1300 1400
Energy (keV) Energy (keV)
20
Energy Resolution (%)
NaI(Tl)
16 GYGAG(Ce)
LaBr3(Ce)
12 SrI2(Eu)
8
4
SrI2(Eu) crystals grown at RMD, Inc. 03 4 5 6 7 8 9 2 3 4 5 6 7 8 9
Cut, polished and encapsulated by LLNL 100 1000
Energy (keV)
Lawrence Livermore National Laboratory
N. CHEREPY cherepy1@llnl.gov 5

6. Official Use Only
Comparison of gamma spectra at 662 keV for ~(1”)3 scintillators
reveals effects of resolution and photopeak efficiency, SPP
CLYC(Ce),
LaBr3(Ce), SrI2(Eu),
f1”x1”
f1.8x2 cm f1”x1”
R=4.3%
R=3% R=3%
NaI(Tl), GYGAG(Ce), Scintillator SPP (662kev)
f1”x1” f1.1”x0.24” for 1”x1” (%)
R=5.8% R=4.7%
LaBr3(Ce) 11.1
SrI2(Eu) 11.4
CLYC(Ce) 5.3
NaI(Tl) 8.5
GYGAG(Ce) 12.8
• For comparison, 1”x1” Ge photopeak efficiency, SPP = 3.9%
• SPP defined as fraction of gammas intercepting detector that lead to photopeak
Lawrence Livermore National Laboratory
N. CHEREPY cherepy1@llnl.gov 6

7. Official Use Only
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
300 1.15
250 1.10
SrI2(Eu): excellent LY
Relative Light Yield
200 proportionality
counts
1.05
150 2.9% at 662 keV
3 1.00
100 1 in encapsulated crystal RMD SrI2(0.5%Eu)
ORNL SrI2(4%Eu)
0.95 ORNL SrI2(6%Eu)
50 Encapsulated RMD SrI2(3%Eu)
NaI(Tl)
0.90 LaBr3(Ce)
0
100 200 300 400 500 600 700 3 4 5 6 7 2 3 4 5 6 7 2 3 4 5 6 7
Energy (keV) 10 100 1000
Electron Energy (keV)
Lawrence Livermore National Laboratory
N. CHEREPY cherepy1@llnl.gov 7

8. We have been working to identify an optimal Gd-based
Official Use Only
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%
2010-11
GYGAG_APD_1710V_-23C_6us
Scale-up of GYGAG(Ce) 5000 GYGAG(Ce) ceramic:
1500
GYGAG(Ce) ceramic:
4000 4.5% at 662 keV w/ PMT 1000
3.9% at 662 keV w/ RMD APD 0.5%
Counts
3.9%
Xc = 417
Counts
3000
2000 500
1000
0 0
1 in3
0 200 400 600
0 100 200 300 400 MCA Channel
Channel
Current status:
 1 in3 parts formed routinely
To optimize performance:
 Photodetector matched to green scintillation
Lawrence Livermore National Laboratory
N. CHEREPY cherepy1@llnl.gov 8

9. Recently we have developed polymer scintillators
Official Use Only
offering energy resolution approaching that of NaI(Tl)
A
3 Backscatter
escape Photopeak
rel. counts
662 keV
FWHM = 9%
2
Compton
Backscatter edge
1
Escape
687 keV • Non-standard polymer that is
formable by methods similar to
0 standard plastic scintillator
B • Bi organometallic, 40 wt%
3
• Current size F1.9x0.17 cm3
rel. counts
Photopeak • Escape peak in small scintillator
2
simulated 3" x 3"
662 keV
FWHM = 6.8% eliminated when larger
1
0
0 200 400 600
Energy (keV)
Lawrence Livermore National Laboratory
N. CHEREPY cherepy1@llnl.gov 9

10. Official Use Only
Materials for future gamma spectrometers?
Gamma Spectroscopy Scintillator Zeff Light Yld En Res, Nonprop SPP,
(Ph/MeV) 662 keV En Res, 662 keV,
662 keV (1 in3)
NaI(Tl) 50 40,000 7% 5.0% 8.5%
LaBr3(Ce) 44 63,000 3% 2.2% 11.1%
Single
SrI2(Eu) 49 90,000 3% 2.2% 11.4%
crystals
(Gd,Y)3(Al,Ga)5O12(Ce) 47 50,000 4.5% 1.9% 12.8%
Garnet
ceramics
Standard PVT 4.5 15,000 8% 3.5% 0
(Compton)
LLNL Bi-loaded polymers 26 10,000- 7% 3.5% 1.5%
Plastics 30,000
Lawrence Livermore National Laboratory
N. CHEREPY cherepy1@llnl.gov 10