The Synthesis and Structures of Elpasolite Halide Scintillators
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1164-L11-05
The Synthesis and Structures of Elpasolite Halide Scintillators Pin Yang1, F. Patrick Doty2, Mark A. Rodriguez1, Margaret R. Sanchez1, Xiaowong Zhou2, and Kanai S. Shah3 1 Ceramics and Glass Processing, Sandia National Laboratories, Albuquerque, NM 87185, U.S.A. 2 Radiation and Nuclear Detection Materials and Analysis, Sandia National Laboratories, Livermore, CA 94550, U.S.A. 3 Radiation Monitoring Devices, Inc. Watertown, MA 02472, U.S.A. ABSTRACT Low-cost, high-performance gamma-ray spectrometers are urgently needed for nonproliferation and homeland security applications. Available scintillation materials fall short of the requirements for energy resolution and sensitivity at room temperature. The emerging lanthanide halide based materials, while having the desired luminosity and proportionality, have proven difficult to produce in the large sizes and low cost required due to highly anisotropic properties caused by the non-cubic crystal structure. New cubic materials, such as the recently discovered elpasolite family (A2BLnX6; Ln-lanthanide and X-halogen), hold promise for scintillator materials due to their high light output, proportionality, and toughness. The isotropic nature of the cubic elpasolites leads to minimal thermomechanical stresses during single-crystal solidification, and eliminates the problematic light scattering at the grain boundaries. Therefore, it may be possible to produce these materials in large sizes as either single crystals or transparent ceramics with high production yield and reduced costs. In this study, we investigated the “cubic” elpasolite halide synthesis and studied the structural variations of four different compounds, including Cs2NaLaBr6, Cs2LiLaBr6, Cs2NaLaI6, and Cs2LiLaI6. Attempts to produce a large-area detector by a hot forging technique were explored. INTRODUCTION Inorganic scintillators, such as NaI (Tl1+) and CsI(Tl1+), are widely used in radiation detectors at room temperature. These materials play an important role for nuclear and particle physics research, medical imaging, nuclear treaty verification and safeguards, nuclear noprofliferatin monitoring, and geological exploration.1 Recent development in the cerium (Ce3+) doped lanthanide halide single crystals, including chlorides2, bromides2-4 and iodides5,6, has shown that these inorganic scintillators exhibit a high light output, a fast decay time, and an outstanding energy resolution, which are excellent for radiation detection applications. However, these single crystals are expensive and difficult to grow in large sizes due to the anisotropic nature of these materials. For example, thermal expansion coefficients for the hexagonal LaBr3 (Space group: P63/m) along its c axis and normal to the prismatic plane are 13.46 X10-6/°C and 28.12 X 10-6/°C, respectively.7 The difference can create large thermomechanical stresses in the crystal during solidification process. Furthermore, these materials have extremely limited ductility and low fracture toughness in comparison to traditional halide salts. Cracks
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