Digital processing of scintillator signals for fast timing applications

Abstract

Fast scintillators such as LaBr 3 (Ce) and CeBr 3 offer new opportunities in gamma-ray detection with good energy and time resolution. Recently, digital signal processing has become a standard in data acquisition for multi-parameter set-ups, since they have a very good performance in terms of energy resolution, dead time and flexibility. Nevertheless digital methods that are able to recover the excellent intrinsic time resolution of fast scintillates are still not widely available. In this paper we report on the results of digital acquisition and processing of signals of LaBr 3 (Ce), CeBr 3 and BaF 2 detectors aimed at obtaining the best time resolution. As a proof of principle we have used a 4-channel oscilloscope with 1 GHz bandwidth and 4 GSa/s sampling rate. Pulses were acquired, stored in memory and analyzed off-line. For each of the three scintillators coincidence measurements at 60Co and 22Na energies were performed against a fast reference BaF 2 + XP2020 detector. Several digital signal-processing methods were used to measure the time resolution for the individual detectors. Constant fraction, threshold and comparator processing were used. The digital processing method that provides the best results is the digital CFD algorithm, yielding time resolution values comparable to those obtained by analog systems. Therefore digital processing is a competitive technique for fast timing with fast scintillators and it holds a strong potential for its implementation in standard set-ups.