Measurements of gamma rays above 3 MeV using 3D position-sensitive 20×20×15 mm3 CdZnTe detectors

Measurements of gamma rays above 3 MeV have been made using a system of 20×20×15 mm
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Cadmium Zinc Telluride semiconductor detectors and the GMI VAS_UM2.3TAT4 application specific integrated circuit (ASIC). These detectors are pixellated with 121 anode pixels and use a grid to help steer the charge carriers to the collecting anode. The measurements looked to explore both the spectroscopic and imaging performance of a system for gamma ray sources above 3 MeV. The ASIC has a dynamic range from about 30 keV up to 3 MeV for the cathode signal and each anode pixel signal. Therefore, measurements of sources above 3 MeV add several challenges, including having to differentiate between events that had a signal reaching the maximum for a single channel and those that did not because of multiple interactions with a single crystal or between multiple crystals. Additionally, events with charge sharing or consisting of interactions in more than one detector constituted a large fraction of the events depositing over 3 MeV in the system and led to degradation of the system performance.