Improvement of the energy resolution in a pixellated CdZnTe detector using depth sensing based on pulse rise-time correlation

Abstract

In this work we present the pulse rise-time method by using signals from one electrode to determine the interaction depth in a 16-pixellated CdZnTe (CZT) detector manufactured by eV Products. Pulse shapes were theoretically calculated by varing the depth in steps of 0.5 mm with fixing the in-plane position. The electric field in the CZT detector was calculated numericallly by using the weighting potential method. The depth information was extracted by the rise-time correlation using calculations for anode pulse shapes. In order to check the accuracy of the pulse shape calculation, we performed a maximum-likelihood fitting process by comparing measured pulse shapes with calculated ones. The pulse shapes were digitally recorded by using a 64-channel 62.5 MS/s digitizer (v1740B) manufactured by CAEN. Gamma rays emitted from a Na-22 standard source were bombarded on the negatively biased contact of the CZT detector. The low energy tail of a photo peak attributed to the hole trapping in the energy spectrum was corrected by using the rise-time correlation. The energy resolution was improved from 9.3% to 6.5% for the 511-keV photo peak with the T-50 rise-time correlation.