Computer simulation of charge trapping and ballistic deficit effects on gamma-ray spectra from CdTe semiconductor detectors

Abstract

In recent years, a variety of special-purpose software has been developed to simulate γ-ray semiconductor detector and associated electronics performances. Unfortunately, these software systems often lack flexibility and cannot be applied outside rather limited ranges. General radiation transport Monte Carlo codes such as ITS and EGS4 can achieve high levels of physical accuracy, but the simulated pulse-height spectra are completely noise free, and therefore differ significantly from experimental results. In this work, the ITS output files have been modified, so as to add to Monte Carlo simulated spectra the subsequent degradation effects inherent in the detection process. Ballistic deficit losses, electronic noise, charge trapping and detrapping are taken into account: the corresponding simulation algorithms are independently combined into the final spectra. As the charge collection efficiency depends upon the position of γ-ray interactions within the bulk, the detector has been virtually sliced into a large number of sections so as to statistically evaluate the spectrum distortion on a local spectra basis. Although the algorithms developed were applied to γ-ray spectra obtained from CdTe detectors only, the generality of the method makes it suitable for any semiconductor detector.