We present the results from testing the performance of CdZnTe (CZT) position-sensitive virtual Frisch-grid (VFG) detectors for gamma-ray imaging. Large-volume CZT detectors with dimensions up to 10x10x30 mm3 recently became available from CZT crystal vendors. Such devices improve detection efficiency and position resolution when integrated into position-sensitive photon counting cameras proposed for nonproliferation, nuclear security, and gamma-ray astronomy. It is important to evaluate the factors affecting the response uniformity and limiting the performance of these detectors. In general, the response non-uniformities could be caused by detector geometries, materials inhomogeneity, and crystal defects. Several techniques have been developed to correct response non-uniformities and improve detector performance. Among them are the high-granularity position-sensitive detectors, which provide the most accurate and robust corrections. Position sensitivity can also be used to reveal response non-uniformities and understand their causes during the detector development or fabrication stages. Here, we describe a technique that we developed for position-sensitive virtual Frisch-grid detectors employing CdZnTe (CZT) and other semiconductors. To illustrate our experimental technique, we measured responses from the selected detectors of different qualities acquired from different vendors and grown by different methods.
TlBr is a promising material for room-temperature semiconductor gamma-ray detectors currently under development by several groups around the world. TlBr has the optimal combination of properties: high atomic number, high density, high mu-tau product, low Fano factor, and lower fabrication cost compared to other materials. The presence of crystal defects and ionic drift-diffusion enchained by the electric field affects the performance of today’s TlBr detectors. As a bias is applied across a detector, a defect distribution inside starts changing due to ion migration. The changes appear to be most pronounced in the first weeks of applying a bias to newly-manufactured crystals during the “conditioning” period. The 3-D position-sensitive detectors provide an opportunity to investigate these processes and their effects on the device performance and on corrections applied to the spectrum. Here, we present results from analyzing response changes in TlBr crystals under applied biases using position-sensitive capacitive Frisch-grid detectors.
This work has been supported by the U.S. Department of Homeland Security, Countering Weapons of Mass Destruction Office, under competitively awarded contract 70RDND18C00000024. This support does not constitute an express or implied endorsement on the part of the Government.
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