Identification of single-pixel incomplete charge collection events by using cathode waveform in pixelated CdZnTe detectors

Abstract

Common grid can steer the electron cloud toward anode pixels to improve the charge collection efficiency in pixelated CdZnTe detectors. Due to insufficient steering and the absence of pixels on the outside of the edge pixels, the whole electron cloud cannot be collected completely by anode pixels for some events, resulting in the incorrect energy reconstruction by the deficient anode signal. Since single-pixel events are mainly used to obtain an excellent spectrum, incomplete charge collection events increase incorrect low-energy counts. However, the cathode signals are intact for incomplete charge collection events, and the cathode slope is related to energy deposition. Therefore, incomplete charge collection on the anode electrode can be identified by using the cathode slope to anode amplitude ratio (S/A). The experiments were performed on a pixelated 20 × 20 × 15 mm3 CdZnTe detector manufactured by Redlen Technologies. Incorrect low-energy counts are significantly decreased by rejecting single-pixel incomplete charge collection events, and the photopeak counts are improved by reconstructing the single-pixel incomplete charge collection events.