New scintillator materials
Band-gap and Defect Engineering for Pyrosilicate Scintillators and Their Temperature Dependence (#2817)
S. Kurosawa1, 2, T. Horiai3, R. Murakami4, A. Yamaji3, Y. Shoji3, 4, K. Kamada1, 3, Y. Ohashi1, Y. Yokota1, A. Yoshikawa1, 3
1 Tohoku University, New Industry Creation Hatchery Center, Sendai, Miyagi, Japan
Ce:(La, Gd)2Si2O7 (Ce:La-GPS) scintillator crystals with a good energy resolution (FWHM) of 5% at 662 keV were obtained, and good scintillation properties were found to be stable up to 450 K. The temperature dependence was found to be related to the band gap energy and defect level; generally, a sample with large energy-deference between the bottom of conduction band and 5d level of Ce3+ can maintain the light output at even high temperature. Here, Ce-doped Y-admix Gd3(Al, Ga)5O12 samples had larger bandgap energy, and light output of Y-admix sample is expected to be remain at high temperature. Thus, Ce:(Gd, La, Y)2Si2O7 crystals were grown by the micro-pulling down method, and temperature dependence of some properties such as scintillation light output, quantum yield excited by UV photons. We found the no difference of the bandgap energy and temperature dependence of QY between Ce:(Gd, La)2Si2O7 and Y-admix sample, while scintillation light output depended on Y-concertation. We show the detail of the results and discuss the band gap structure and defect in this paper.
Keywords: Pyrosillate, scintillator, temperature dependence, oil well logging
Synthesis of Ce3+ doped nanocrystalline BaGdF5 glass-ceramics for gamma ray spectroscopy (#3445)
C. T. Struebing1, B. Beckert2, J. Nadler2, B. Wagner1, Z. Kang1
1 GTRI, ELSYS, Atlanta, Georgia, United States of America
Detection of radiation has become an increasingly important field due to its prevalence in medical and homeland security operations. One of the preferred current methods of detection uses single crystal scintillators as the detection medium for their good energy resolution. Unfortunately, single crystal scintillators are expensive to produce and are vulnerable to heat, mechanical shock, and moisture. Glass-ceramic scintillators can be produced inexpensively and do not suffer from these vulnerabilities. If glass ceramics can reach a competitive level of energy resolution they provide a cheaper alternative to single crystals. Silicate based glass-ceramic scintillators containing BaGdF5 nanocrystals have been produced via the melt quench method. Constituent powders were mixed, melted at 1500ºC for 6hrs, quenched in a 400ºC graphite mold, and annealed at different temperatures for nanocrystal precipitation. The scintillators have been optimized for increased density of over 4.3 g/cm3 to improve gamma radiation stopping power. GdF3 were incorporated and found out to promote nucleation of nanoparticles in pursuit of greater light output. Currently an energy resolution of 16% has been achieved under 662 keV irradiation during gamma ray excited spectra measurements for the Ce3+ doped BaGdF5 glass ceramics and further optimizations will be reported.
Keywords: scintillators, gamma detection, nanocrystals, transparent glass ceramic, nanocomposite
Cesium Hafnium Chloride: A Non-Hygroscopic, High-Performance Scintillator (#3195)
S. Lam1, A. Burger2, S. Motakef1
1 CapeSym, Inc., Natick, Massachusetts, United States of America
Cesium hafnium chloride (CHC, Cs2HfCl6) is a recently-discovered material with superior radiation detection properties relative to the incumbent detectors NaI(Tl) and CsI(Tl). Advantages of CHC include: an excellent energy resolution, no self-absorption, no self-radioactivity, and non-hygroscopicity. Our first-grown crystals were measured to have a light yield of 30,000 ph/MeV and an energy resolution of 3.3%. With a decay time close to 4 microseconds, CHC is well-suited to most low-count scenarios encountered in homeland security applications. This presentation will address techniques for charge purification and preparation, crystal growth by the Bridgman technique, as well as the challenges associated with this line compound. Finally, we will discuss the use of alloying to reduce the decay time to 2 microseconds.
This work has been supported by the U.S. Department of Department of Energy, Office of Science, under competitively awarded contract DE-SC0015733. This support does not constitute an express or implied endorsement on the part of the Government.
Keywords: Cesium hafnium chloride, scintillator, gamma detection, crystal growth, characterization
Synthesis and Characterization of Cs2HfCl6 Transparent Ceramic Scintillator (#1610)
W. B. Goodwin1, A. Burger1, 2, A. Hunsaker1, E. Rowe1, N. J. Cherepy3, S. A. Payne3
1 Fisk University, Department of Life and Physical Sciences,, Nashville, Tennessee, United States of America
We have developed Cs2HfCl6 transparent ceramics by hot uniaxial pressing and investigated the scintillation properties, in comparison to its single crystal counterpart. Cs2HfCl6 crystal structure is cubic and isostructural to that of K2PtCl6. It is non-hygroscopic, has a high Zeff number of 58, and light yields of up to 54,000 ph/MeV and low nonproportionality as measured in single crystals. For ceramic pressing, Cs2HfCl6 powders were placed in a 13 mm diameter die and uniaxial pressed at 50,000 PSI for 280°C for 70 h. The sample surface was polished after pressing and was optically transparent. The light yield was measured using a photomultiplier tube and found to be 25,900 photons/MeV with an energy resolution of 11% at 662 keV. The principal decay time was found to be 4.13 µs and is comparable to its single crystal counterpart. To date, Cs2HfCl6 has best energy resolution for a ceramic halide and over 4 times as bright as BaF2-Ce(0.2%) and CaF2 ceramic scintillators.
Keywords: Ceramic, Energy Resolution, Transparent ceramic, Scintillator, Scintillation decay time
Advancements in KSr2I5:Eu2+ scintillators (#3706)
L. M. Stand1, 4, M. Zhuravleva1, 2, J. Johnson1, 2, M. Loyd1, 2, M. Koschan1, E. D. Lukosi3, C. L. Melcher1, 2
1 University of Tennessee, Scintillation Materials Research Center, Knoxville, Tennessee, United States of America
For this work we focused our efforts on optimizing the growth parameters required to grow one-inch diameter KSr2I5:Eu crystals at pulling rates between of 5 to 10 mm/h. Crack free single of KSI:Eu measuring up to Ø 1" by 6" were grown via the vertical Bridgman technique. The scintillation properties were evaluated using specimen volumes ranging from 12 cm3 to 54 cm3 and energy resolution as low as 3.1% were measured for 12 cm3 crystals.
We investigated anion and cation substitution to enhance the light yield and energy resolution of KSr2I5:Eu. Solid solutions of KSr2BrxI(5-x):Eu 4% and KSr2(1-x)Ba2xI5:Eu 4% (where 0.05 ≤ x ≤ 1) were investigated. We found that replacing some of the matrix iodine atoms in KSr2I5:Eu with bromine increased the light yield by 10% while maintaining similar energy resolution. The highest light yield was measured for KSr2Br0.10I4.90:Eu 4% with 97,900 ph/MeV and 3.0% at 662 keV. We found that by replacing some Sr2+ for Ba2+, forming KSr1.3Ba0.7I5:Eu 4% increased the light yield and improved the energy resolution. The light yield increased from 84,000 ph/MeV to 120,000 ph/MeV and the energy resolution improved from 3.0% to 2.3% for a 1 cm3 sample.
Keywords: Single crystal growth, Bridgman technique, Halides, Potassium compounds, Scintillators
Transparent Ceramic Scintillators for Gamma Spectroscopy and Imaging (#3597)
N. Cherepy1, Z. Seeley1, S. Payne1, E. Swanberg1, P. Beck1, D. Schneberk1, G. Stone1, B. Wihl1, S. Fisher1, P. Thelin1, T. Stefanik3, J. Kindem4
1 Lawrence Livermore Natinoal Laboratory, Livermore, California, United States of America
New transparent ceramic scintillators offer advantages for applications in gamma spectroscopy and X-ray imaging. For gamma spectroscopy, excellent light yield, material uniformity, light yield proportionality, mechanical and environmental ruggedness can be achieved in polycrystalline ceramic oxide garnets. We have fabricated 5 in3 Ce-doped Gd garnet transparent ceramics. GYGAG(Ce) garnet transparent ceramics offer r = 5.8g/cm3, Zeff = 48, principal decay of <100 ns, and light yield of 50,000 Ph/MeV. When pixelated, we obtain R(662 keV) = 3.0%, for GYGAG(Ce) with silicon photodiode readout. For lens-coupled radiographic imaging, thin transparent scintillators without optical scatter are required. The transparent ceramic bixbyite scintillator, (Gd,Lu,Eu)2O3, or “GLO,” offers excellent x-ray stopping, due to its Zeff = 68 and density of 9.1 g/cm3. High transparency is achieved by minimizing the formation of secondary phases by adding Gd to the Lu2O3 structure. 12” x 12” GLO imaging plates outperform scintillator glass for MeV radiography, due to higher light yield (55,000 Ph/MeV) and better stopping, while providing spatial resolution of >8 lp/mm for MeV X-rays.
Keywords: ceramic scintillator, gamma spectroscopy, imaging plates, scintillator, transparent ceramics