Performance Calculation of Pulse Shape Discrimination Based on Photoelectron Quantity

TL;DR

This paper evaluates the effectiveness of pulse shape discrimination in liquid scintillators for neutron and gamma-ray separation, highlighting the minimum photoelectron count needed for high discrimination efficiency.

Contribution

It introduces a simulation-based method to assess PSD performance relative to photoelectron quantity, providing practical thresholds for effective neutron-gamma discrimination.

Findings

At least 49 photoelectrons are needed for 90% neutron rejection.

Gamma-like events are correctly identified with 97.8% efficiency.

The study combines experimental decay time measurements with waveform simulation.

Abstract

Pulse Shape Discrimination (PSD) is a widely used technique in many experimental analysis. In this study, we specifically aimed to assess the effectiveness of PSD in accurately measuring decay time. We measured the decay times of a 0.1 wt% Gd-loaded liquid scintillator (Gd-LS) with 5 vol% Ultimagold-F added when irradiated with neutrons and gamma rays, which were emitted from a Cf-252 radiation source, using a two-exponential decay model. We distinguished between gamma-like events and neutron-like events using the time-of-flight difference. Based on the measured decay times, we developed a simulation to model the waveforms. In the sim-ulation, we adjusted the number of photoelectrons (NPE) and generated waveforms for NPE ranging from 10 to 1000 photoelectrons. We investigated the pulse shape discrimination (PSD) performance as a function of NPE photoelectrons (PE) and determined that at least 49 PE is required for a neutron-like events rejection efficiency of 90%, while keeping gamma-like events 97.8%.