Stability and characteristics of 3D HgI2 detectors at different cathode bias

This article presents our studies on the first fully pixelated 3-dimensional (3D) position-sensitive HgI₂ detectors, manufactured by Constellation Technology Corporation. The radiation signals were read out using a VAS_UM3.2/TAT4 ASIC readout system. The performance of several detectors was investigated over a period of time and at different operational bias voltages. The resolution for single-pixel-triggered events was measured as good as 1.60% at 662 keV. 1.20% FWHM energy resolution was observed on the best anode pixel, demonstrating the potential to achieve better resolution on HgI₂ detectors. It was found that the trapping of electrons is much lower in those HgI₂ detectors. The resolution changes inside the detector bulk are minor. The stability of the detectors was examined and all detectors with the history of being biased up within one month show little variance of photopeak centroid and resolution. However, one detector unbiased for three months is found to have performance variance over time. Slight improvement of resolution with cathode bias raised from -3000 V to -4000 V is observed.