Fine-scale spatial response of CdZnTe radiation detectors

Several studies have suggested that the uniformity of Cadmium Zinc Telluride (CZT) detectors play an important role in their performance when operated as gamma-ray spectrometers [1]. However, the detailed gamma response of simple planar detectors as a function of position over the device area is largely unknown. To address this issue we have built a system capable of measuring the detector response with a resolution of similar to 250 mu m. The system consists of a highly collimated (similar to 200 mu m) photon source (<150 keV) scanned over the detector using a computer controlled, two-axis translation stage, Fifteen samples configured as planar detectors were examined with the new apparatus. The material grade of the detectors examined varied from "counter" to "select discriminator". Two classes of spatial response variation were observed and are presented here. Infrared (IR) transmission images were also acquired for each sample and correlation between features in the pulse height spectrum and crystalline defects were observed.