Evaluation of Melt-Grown, ZnO Single Crystals for Use as Alpha-Particle Detectors

As part of an ongoing investigation of the scintillation properties of zinc-oxide-(ZnO)-based scintillators, several melt-grown, ZnO single crystals have been characterized using alpha-particle excitation, infrared reflectance, and room temperature photoluminescence. The crystals, grown by Cermet, Inc., using an oxygen-pressurized melt-growth process, were doped with Group 1 elements (Li), Group 2 elements (Mg), Group 3 elements (Ga, In) and lanthanides (Gd, Er, Tm). The goals of these studies are to better understand the scintillation mechanisms associated with various members of the ZnO scintillator family and to then use this knowledge to improve the radiation detection capabilities of ZnO-based scintillators. One application for which ZnO is particularly well suited as a scintillator is as the associated particle detector in a deuterium-tritium (D-T) neutron generator. Application requirements include the exclusion of organic materials, outstanding timing resolution, and high radiation resistance. ZnO:Ga and ZnO:In have demonstrated fast (subnanosecond) decay times with relatively low light yields, and ZnO(Ga) has been used in a powder form as the associated particle detector for a D-T neutron generator. Four promising candidate materials, ZnO, ZnO:Ga, ZnO:In,Li, and ZnO:Er,Li, were identified in this study. These four samples demonstrated sub-nanosecond decay times and alpha-particle-excited- luminescence comparable to BC-400 fast plastic scintillator. The ZnO:Mg,Ga, ZnO:Gd, and ZnO:Li samples demonstrated appreciable slow (microsecond) decay components that would be incompatible with high-counting-rate applications.