A System for the Characterization and Testing of CdZnTe/CdTe Pixel Detectors for X-ray and Gamma-ray Imaging

We have developed an automated system for the characterization and testing of CdZnTe/CdTe pixel detectors for x-ray and gamma-ray imaging. A set of custom made pogo-pin arrays and corresponding detector holders have been designed for a precise, non-damaging loading and unloading of detectors to a "measurement habitat" within the system. The architecture of the system is flexible, allowing measurements of current, spectral responses and pulse shapes from individual detector pixels. A multi-channel read-out (up to 256 channels) based on CMOS switches make possible the monitoring of leakage-and /or x-ray induced photo-currents sequentially for all individual pixels, for groups of pixels, or for the full detector with different voltage ramping scenario. A measurement of spectral pixel responses can be done with a Single-Photon-Counting ASIC for up to 256 pixels simultaneously, or from individual pixel(s) with discrete read-out electronics. The test system can satisfy many experimental needs including measurements of a detector's: 1) temporal response under x-ray or gamma ray irradiation; 2) photon count rate performance; 3) bulk/contact charge transport properties; 4) guard ring or/and passivation effectiveness, and 5) long term stability. Control and data acquisition can be conducted with a local computer, or via the Internet. The system has been successfully operated for about 2 years. Examples of the results obtained with detectors fabricated from different material vendors are presented.