Experimental comparison of the measurement results of two different silicon photomultipliers and organic scintillator to detect fast neutrons

Abstract

We report on the study of experimental comparison between the results of two types of silicon photomultiplier (SiPM), to discriminate the signals from fast neutrons and gamma-rays by the digital charge pulse shape discrimination (PSD) method. This uses a total to partial charge ratio analysis. The signals are digitized by a high-speed digital oscilloscope LeCroy WR 620zi with a sample rate of 10 GS/s. This oscilloscope was used to acquire data, which were later processed offline in a specially developed software package written in LABVIEW. The tested detector part consisted from a stilbene crystal (3x3x6 mm3 and 6x6x6 mm3) optically coupled to a SiPM (KETEK 3x3 mm2 and SensL 6x6 mm2 respectively) as a photodetector. Measurements with a Cf-252 source were performed and a figure of merit (FOM) for discrimination between neutron and gamma-ray was calculated for each assembly. The resulting value of FOM for the KETEK 3x3 mm2 SiPM and SensL 6x6 mm2 SiPM was 1.6±0.03 and 1.76±0.05, respectively, the SensL assembly having a slightly better discrimination factor than KETEK one. The obtained results prove a good fast neutron detection performance of the SiPMs, which makes it possible to use these types of neutron detectors in the several fields of radiation protection applications and safety of nuclear facilities.