Proton discrimination in CLYC for fast neutron spectroscopy

TL;DR

This paper presents a novel pulse shape discrimination method in CLYC scintillators that effectively separates proton signals from other charged particles, enabling improved fast neutron spectroscopy without time-of-flight measurements.

Contribution

Introduction of a multi-gate charge integration algorithm for particle discrimination in CLYC, enhancing its capability for fast neutron spectroscopy.

Findings

Effective separation of protons and heavier charged particles achieved

Pulse shape differences observed across various time scales

Validation of discrimination algorithm using TOF data

Abstract

The Cs$_2$LiYCl$_6$:Ce (CLYC) elpasolite scintillator is known for its response to fast and thermal neutrons along with good $\gamma$-ray energy resolution. While the $^{35}$Cl($n,p$) reaction has been identified as a potential means for CLYC-based fast neutron spectroscopy in the absence of time-of-flight (TOF), previous efforts to functionalize CLYC as a fast neutron spectrometer have been thwarted by the inability to isolate proton interactions from $^{6}$Li($n,\alpha$) and $^{35}$Cl($n,\alpha$) signals. This work introduces a new approach to particle discrimination in CLYC for fission spectrum neutrons using a multi-gate charge integration algorithm that provides excellent separation between protons and heavier charged particles. Neutron TOF data were collected using a $^{252}$Cf source, an array of EJ-309 organic liquid scintillators, and a $^6$Li-enriched CLYC scintillator outfitted with fast electronics. Modal waveforms were constructed corresponding to the different reaction channels, revealing significant differences in the pulse characteristics of protons and heavier charged particles at ultrafast, fast, and intermediate time scales. These findings informed the design of a pulse shape discrimination algorithm, which was validated using the TOF data. This study also proposes an iterative subtraction method to mitigate contributions from confounding reaction channels in proton and heavier charged particle pulse height spectra, opening the door for CLYC-based fast neutron and $\gamma$-ray spectroscopy while preserving sensitivity to thermal neutron capture signals.