Pulse shape discrimination system for room-temperature semiconductor detectors

Abstract

Easily adjustable pulse shape discrimination (PSD) system effectively operating in the wide range of registered energies is offered. Shape distortions of the detector output signal due to charge losses are clearly visible if one carries out shape analysis of the spectrometric signal for pulses restored up to the rectangular shape. The essence of the method consists in the analysis of difference of a restored signal form from rectangular. For this purpose the area of a pulse is measured within the given interval at once after incoming pulse and within the same time interval delayed concerning first. In case of an inequality of these areas, the signal is considered deformed and is not exposed to further analysis. Schematic decision and operation mode of PSD system is analysed, pulses diagrams are presented. The developed PSD system was applied in gamma-spectrometer with planar geometry CdTe detector with dimentions 5×5×3 mm 3. Detector had m–s–m structure with gold electrode. Initial energy resolution of the detector was 17 keV at 662 keV and peak-to-Compton ratio equal to 1.8. The PSD application improves energy resolution up to 3.2 keV and peak-to-Compton ratio to about 5.0. At this essential reduction of count rate (up to 75%) in a maximum of a total absorption peak is observed. But the energy resolution of about 6 keV can be received at insignificant (not more than 20%) reduction of count rate. Spectra of 137Cs and 133Ba obtained with and without PSD system application are shown. Diagrams of energy resolution at 662 keV line as well as count rate in the total absorption peak maximum versus pulse shape discrimination level are presented.