Scintillator materials for gamma ray spectroscopy cherepy forexternal
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    Scintillator materials for gamma ray spectroscopy cherepy forexternal Scintillator materials for gamma ray spectroscopy cherepy forexternal Presentation Transcript

    • 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-468519This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344
    • Official Use Only OverviewRequirements for new detector materials:1) High energy resolution and stopping — to discriminate gamma spectra2) Low cost / maintenance — starting materials; growth / ruggedness3) 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
    • For radioisotope identification, gamma scintillators with Official Use Onlyhigh 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
    • Inorganic single crystal and ceramic Only Official Use scintillators are beingdeveloped 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 importantmaterials- 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
    • Official Use OnlyFor gamma ray spectroscopy, SrI2(Eu) comparable to LaBr3(Ce) andGYGAG(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
    • Official Use OnlyComparison of gamma spectra at 662 keV for ~(1”)3 scintillatorsreveals 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
    • 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 proportionalitycounts 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
    • 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 50,000En. Res. (662 keV) ___ 11% ___ 11% 10% 9% 4-5% 2010-11 GYGAG_APD_1710V_-23C_6usScale-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
    • Recently we have developed polymer scintillators Official Use Only offering energy resolution approaching that of NaI(Tl) A 3 Backscatter escape Photopeakrel. 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 cm3rel. 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
    • 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% Garnetceramics 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