Gamma scanning of large-volume CdZnTe detectors to map their efficiency

An automated, computer-controlled scanning device to map the sensitivity of large-volume CdZnTe gamma detectors is described. It is of modular design and fully based on moderately priced commercial components. The collimated radiation source is moved in X–Y direction over the radiation detector under test using stepping motors. Synchronously, gamma spectra are taken for each X–Y position. Different regions of interest in a spectrum can be evaluated or re-evaluated and the measured gamma countrate (peak area) is displayed and documented in contour maps as a function of the X–Y coordinate. The system is meant for evaluation of new, large-volume room temperature semiconductor detectors and for quality-control measurements on detectors which are used in the Department of Safeguards for the verification of nuclear material.