Characterisation of a New Type of Solid Organic Scintillator for neutron-gamma Discrimination using Pulse-Shape DiscriminationTechniques

Abstract: In this report the neutron-gamma discrimination capabilities of the new type of solid organic scintillator, EJ-299-33, was investigated using several pulse-shape discrimination (PSD) techniques. Among others, the analog zero-crossing method andthe digital charge-comparison and integrated-rise-time method were tested. The parameters of the digital PSD methods were optimised individually and the figure-of-merit was measured for each method and compared in different energy windows. The photoelectron yield of the setup was measured using two different photomultiplier tubes (PMT), a 3 inch diameter ET 9821 and a 5 inch diameter ET 9390KB. The highest photoelectron yield was measured with the ET 9390KB, which was the PMT used for the neutron-gamma discrimination capability measurements. In this work, four decay constants were found for the scintillator decay times. These were found by fitting average neutron and gamma-ray waveforms with the convolution of severeal exponential functions, that describes the light emission intensity of the scintillator, with an approximation of the PMT response function. Thebest agreement was found for the assumption that the scintillator light emission intensity is governed by four decay constants. The intensity of the two slowest components contain information about the incident particle.