Enhanced time response of 1-in. LaBr_3(Ce) crystals by leading edge and constant fraction techniques

Abstract

We have characterized in depth the time response of three detectors equipped with cylindrical LaBr_3(Ce) crystals with dimensions of 1-in. in height and 1-in. in diameter, and having nominal Ce doping concentration of 5%, 8% and 10%. Measurements were performed at Co-60 and Na-22 gamma-ray energies against a fast BaF2 reference detector. The time resolution was optimized by the choice of the photomultiplier bias voltage and the fine tuning of the parameters of the constant fraction discriminator, namely the zero-crossing and the external delay. We report here on the optimal time resolution of the three crystals. It is observed that timing properties are influence('by the amount of Ce doping and the crystal homogeneity. For the crystal with 8% of Ce doping the use of the ORTEC 935 CFD at very shorts delays in addition to the Hamamatsu R9779 PMT has made it possible to improve the LaBr3(Ce) time resolution from the best literature value at Co-60 photon energies to below 100 ps. (C) 2015 Elsevier B.V. All rights reserved.