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Atomistic models for scintillator discovery

Doty, Fred P.; Yang, Pin Y.

A2BLnX6 elpasolites (A, B: alkali; Ln: lanthanide; X: halogen), LaBr3 lanthanum bromide, and AX alkali halides are three classes of the ionic compound crystals being explored for {gamma}-ray detection applications. Elpasolites are attractive because they can be optimized from combinations of four different elements. One design goal is to create cubic crystals that have isotropic optical properties and can be grown into large crystals at lower costs. Unfortunately, many elpasolites do not have cubic crystals and the experimental trial-and-error approach to find the cubic elpasolites has been prolonged and inefficient. LaBr3 is attractive due to its established good scintillation properties. The problem is that this brittle material is not only prone to fracture during services, but also difficult to grow into large crystals resulting in high production cost. Unfortunately, it is not always clear how to strengthen LaBr3 due to the lack of understanding of its fracture mechanisms. The problem with alkali halides is that their properties decay rapidly over time especially under harsh environment. Here we describe our recent progress on the development of atomistic models that may begin to enable the prediction of crystal structures and the study of fracture mechanisms of multi-element compounds.

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TYPE Conference YEAR 2010
OSTI

Cerium doped elpasolite halide scintillators

Doty, Fred P.; Zhou, Xiaowang Z.; Noda, Frank T.

Low-cost, high-performance gamma-ray spectrometers are urgently needed for proliferation detection and homeland security. The cost and availability of large scintillators used in the spectrometer generally hinge on their mechanical property and crystal symmetry. Low symmetry, intrinsically brittle crystals, such as these emerging lanthanide halide scintillators, are particularly difficult to grow in large sizes due to the development of large anisotropic thermomechanical stresses during solidification process. Isotropic cubic scintillators, such as alkali halides, while affordable and can be produced in large sizes, are poor spectrometers due to severe nonproportional response and modest light yield. This work investigates and compares four new elpasolite based lanthanide halides, including Cs2LiLaBr6, Cs2NaLaBr6, Cs2LiLaI6, and Cs2NaLaI6, in terms of their crystal symmetry, characteristics of photoluminescence and optical quantum efficiency. The mechanical property and thermal expansion behavior of the cubic Cs2LiLaBr6 will be reported. The isotropic nature of this material has potential for scaled-up crystal growth, as well as the possibility of low-cost polycrystalline ceramic processing. In addition, the proportional response with gamma-ray energy of directionally solidified Cs2LiLaBr6 will be compared with workhorse alkali halide scintillators. The processing challenges associated with hot forged polycrystalline elpasolite based lanthanide halides will also be discussed.

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TYPE Conference YEAR 2010
OSTI
Results 51–75 of 100
Results 51–75 of 100