Thallium Bromide as an Alternative Material for Room-Temperature Gamma-Ray Spectroscopy and Imaging.

TlBr Gamma-Ray Spectrometer and Imager;Nuclear Engineering and Radiological Sciences;Engineering;Nuclear Engineering and Radiological Sciences

Koehler, WilliamFlaska, Marek ;

University of Michigan

关键词: TlBr Gamma-Ray Spectrometer and Imager;    Nuclear Engineering and Radiological Sciences;    Engineering;    Nuclear Engineering and Radiological Sciences;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/133299/koehlerw_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Thallium bromide is an attractive material for room-temperature gamma-ray spectroscopy and imaging because of itshigh atomic number (Tl: 81, Br: 35), high density (7.56 g/cm^3), and a wide bandgap (2.68 eV). In this work, 5 mm thick TlBr detectors achieved0.94% FWHM at 662 keV for all single-pixel events and 0.72% FWHM at 662 keV from the best pixel and depth using three-dimensional position sensing technology. However, these results were limited to stable operation at -20 C. After days to months of room-temperature operation, ionic conduction caused these devicesto fail. Depth-dependent signal analysis was used to isolate room-temperature degradation effects to within 0.5 mm of the anode surface. This was verified by refabricating the detectors after complete failure at room temperature; after refabrication, similar performance and functionality was recovered. As part of this work, the improvement in electron drift velocity and energy resolution during conditioning at -20 C was quantified. A new method was developed to measure the impurity concentration without changing the gamma ray measurement setup. The new method was used to show that detector conditioning was likely the result of charged impurities drifting out of the active volume. This space charge reduction then caused a more stable and uniform electric field. Additionally, new algorithms were developed to remove holecontributions in high-hole-mobility detectors to improvedepth reconstruction. Thesealgorithms improved the depth reconstruction (accuracy) without degrading the depth uncertainty (precision). Finally,spectroscopic and imaging performance of new 11~x~11 pixelated-anode TlBr detectors was characterized. The larger detectors were used to show thatenergy resolution can be improved by identifying photopeak events from their Tl characteristic x-rays.