Digital pulse-shape discrimination of fast neutrons and gamma rays

TL;DR

This study demonstrates that digital pulse-shape discrimination techniques can effectively distinguish fast neutrons from gamma rays in liquid scintillators, with performance comparable or superior to traditional analogue methods, using optimized sampling parameters.

Contribution

The paper introduces and compares four digital pulse-shape analysis algorithms for neutron-gamma discrimination, showing digital methods can outperform analogue systems with appropriate ADC specifications.

Findings

Digital algorithms achieve similar or better discrimination figures-of-merit than analogue.

A 12-bit, 100 Ms/s ADC suffices for optimal discrimination in the studied energy range.

Sampling frequency influences time resolution, with 100 Ms/s yielding 1.7 ns FWHM.

Abstract

Discrimination of the detection of fast neutrons and gamma rays in a liquid scintillator detector has been investigated using digital pulse-processing techniques. An experimental setup with a 252Cf source, a BC-501 liquid scintillator detector, and a BaF2 detector was used to collect waveforms with a 100 Ms/s, 14 bit sampling ADC. Three identical ADC's were combined to increase the sampling frequency to 300 Ms/s. Four different digital pulse-shape analysis algorithms were developed and compared to each other and to data obtained with an analogue neutron-gamma discrimination unit. Two of the digital algorithms were based on the charge comparison method, while the analogue unit and the other two digital algorithms were based on the zero-crossover method. Two different figure-of-merit parameters, which quantify the neutron-gamma discrimination properties, were evaluated for all four digital algorithms and for the analogue data set. All of the digital algorithms gave similar or better figure-of-merit values than what was obtained with the analogue setup. A detailed study of the discrimination properties as a function of sampling frequency and bit resolution of the ADC was performed. It was shown that a sampling ADC with a bit resolution of 12 bits and a sampling frequency of 100 Ms/s is adequate for achieving an optimal neutron-gamma discrimination for pulses having a dynamic range for deposited neutron energies of 0.3-12 MeV. An investigation of the influence of the sampling frequency on the time resolution was made. A FWHM of 1.7 ns was obtained at 100 Ms/s.