Tl-based elpasolites for radiation detection

Preventing the proliferation of nuclear materials is critical in maintaining national security and safety. One key method is to identify Special Nuclear Materials (SNM) through their characteristic gamma-ray radiation and neutron emissions. None of the detectors available at present meet the key requirements of high energy resolution, high detection efficiency and low cost. The goal of the proposed effort is to develop new scintillating materials capable of detecting gamma-rays with very high efficiency and energy resolution, and make them available at low cost. Simultaneous detection of neutrons with high efficiency will be possible, providing further reduction in cost and making the eventual instruments more compact. In Phase I we studied Ce-doped Tl-based elpasolite compounds, including Tl2LiYCl6, Tl2LiLaBr6, Tl2LiYBr6, Tl2LiLaCl6, and Tl2LiGdBr6. Emphasis was put on TLYC crystal growth and studies on its various scintillation properties, including light yield, emission wavelength, as well as effects of Ce concentration on the basic scintillation properties. Phase I concluded with a successfully grown 1"×1.2" TLYC single crystal, with an energy resolution of 3.9% at 662 keV. In Phase II program we will focus on developing these Tl-based elpasolite scintillators, with energy resolution of <3% at 662 keV, for crystals with sizes up to 2"×2". In the first year of Phase II, we will further explore the family of Tl-based elpasolites in order to select the most promising composition for scale-up in the second year. The Phase II project will conclude with construction of dual mode detector assemblies up to 2"×2" Tl-elpasolites, coupled to appropriate light sensors and associated readout electronics. A system capable of detection gamma-ray and neutrons with high gamma-ray energy resolution can be easily incorporated in nuclear non-proliferation and homeland security instruments. Moreover, fields such as nuclear physics, medical imaging, oil well logging and material sciences will also benefit from such detectors and systems. The proposed research will develop new radiation detectors for enhancing the capabilities of systems used in detecting the spread of nuclear materials. These detectors will also find applications in physics research, medical imaging, oil well logging and material studies.