Fast neutron - gamma pulse shape discrimination of liquid scintillation signals for time correlated measurements

Abstract

We describe a neutron/gamma pulse shape discrimination (PSD) system that overcomes count rate limitations of previous methods for distinguishing neutrons from gammas in liquid scintillation detectors. Previous methods of PSD usually involve pulse shaping time constants that allow throughput of tens of thousands counts per second. Time correlated measurements require many millions of counts per second to accurately characterize nuclear material samples. To rapidly inspect many test articles, a highthroughput system is desired. To add neutron -gamma distinction to the analysis provides a much desired enhancement to the characterizations. However, if the PSD addition significantly slows down the inspection throughput, this PSD feature defeats any analysis advantage. Our goal for the fast PSD system is to provide sorted timing pulses to a fast, multi-channel, time-correlation processor at rates approaching several million counts per second enabling high throughput, enhanced inspection of nuclear materials.

A background-free direction-sensitive neutron detector

“…Other standard neutron detectors currently in use include the 3 He based Bonner sphere technique [6], pulse shape discrimination in organic scintillators to distinguish elastic collisions of neutrons with protons from gamma ray signals [7][8], and various schemes making use of other exoergic thermal neutron capture reactions (including e.g.…”