Characterization of CZT Detectors for the ASIM Mission

The National Space Institute, of the Technical University of Denmark is responsible for the selection and characterization of the CZT detector crystals for the X- and Gamma-ray instrument, MXGS, onboard ESA´s Atmospheric Space Interaction Monitor (ASIM) mission. The first CZT pixel detector modules for MXGS have recently been delivered by Redlen. Measurements at the University of Bergen demonstrate that the detectors exhibit the expected spectral performance; however, it was also found that the detector modules showed unexplained pixel-to-pixel count rate variations. At The National Space Institute a series of measurements were initiated focusing on the pixel-to-pixel count rate variations. Collimated monochromatic X-ray beams were used to scan a number of Redlen pixel detectors. The main conclusion of these measurements is that the pixel-to-pixel count rate variations are correlated with variations in the effective pixel areas. These variations are likely related to non-uniformity of the internal electric detector field.