Digital processing of signals from LaBr3: Ce scintillation detectors

Abstract

In this paper, we report on the results of digital signal processing of LaBr3(Ce) detectors. The photomultiplier (PMT) output signals from two cylindrical LaBr3(Ce) detectors (1.5" diameter and 2" tall) were directly digitized with an ultrafast digitizer (sampling rate up to 4 GSample/s and 10-bits resolution) and the energy and timing information were extracted through offline analysis of the pulses. It is shown that at high sampling rates (4 GS/s) a simple integration of pulses is sufficient to reproduce the analogue energy resolution of the detectors (3.5% at 662 keV energy) and by employing a digital version of constant-fraction discrimination (CFD) timing a time resolution of 240 ps (FWHM) is achieved at the energy lines of 60Co. The effects of pulse sampling rate were studied, indicating a degradation of the performance of the detectors with reducing the pulse sampling rate. In particular, it was found that at sampling rates below 1 GS/s, the digital timing can be limited by the aliasing error. By using an anti-aliasing filter, a time resolution of 375 ps (FWHM) and an energy resolution of 3.5% at 662 keV were achieved with a sampling rate of 500MS/s.