Analysis of system-dependent factors affecting pixelated CdZnTe detector performance through simulation

Charge sharing and weighting potential cross-talk between pixels are important factors that degrade the energy resolution in multiple-pixel events. However, simulation studies indicate that these factors cannot fully explain the measured energy resolution degradation for multiple-pixel events nor the Compton image distortion observed in some detector systems. This work presents simulation-based analysis of additional factors that degrade the performance of pixelated CdZnTe detectors coupled to the Gamma Medica Ideas (GMI) VAS UM/TAT4 ASIC and the H3Dv2 ASIC from Brookhaven National Laboratory (BNL). The peak-hold circuitry in the GMI ASIC cannot properly hold the signal amplitude while the BNL ASIC does not have this problem. The impact of this peak-hold drop on the energy resolution is studied for multiple-pixel events and a calibration technique to overcome this effect is validated. Many CdZnTe detectors have non-uniform performance on a pixel-by-pixel basis. The impact of single-pixel energy resolution non-uniformity is studied for multiple-pixel events. The GMI ASIC uses a simple threshold time pick-off with the common start of the system triggered by the cathode, while the BNL ASIC uses the peaking time with the common start triggered by the anode. The impacts of these schemes are isolated and analyzed through simulation. Overall, the simulation package considers gamma-ray interactions within the CdZnTe crystal, charge induction, electronic noise, pulse shaping, peak-hold drop and ASIC triggering procedures. The simulation package considers different timing pick-off techniques for both the GMI VAS UM/TAT4 ASIC and the H3Dv2 ASIC.