Assessing the suitability of three proxy sources for the development of detectors of special nuclear materials

Matthew P Taggart,Chris Allwork,Michael Collett,Paul J Sellin,Michael W J Hubbard

doi:10.1088/1361-6498/ab9fdb

Matthew P Taggart, Chris Allwork + Show 3 more

Open Access

https://doi.org/10.1088/1361-6498/ab9fdb

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Abstract

Numerous techniques and equipment have been developed to provide a capability for the detection of special nuclear materials (SNM), but due to the necessary security measures surrounding these materials alternate, or proxy, neutron sources are often utilised in their stead. In this paper we report the neutron and gamma pulse shape discrimination response of plastic scintillator to mixed neutron/gamma beams produced from two radionuclide neutron sources, and also from an SNM source of weapons-grade plutonium. We discuss the suitability of using radionuclide sources, with appropriate shielding configurations as proxy sources for SNM.A 3σnth-γ discrimination level has been achieved for an SNM source at a low-level energy threshold of ∼220 keVee when a shielding configuration of 5 cm of lead was implemented. Varying amounts of lead and high-density polyethylene (HDPE) shielding were also investigated with the 3σ limit being reached by ∼240 keVee.This work shows that an AmBe neutron source serves as an appropriate SNM proxy achieving a comparable value for figure of merit above ∼1 MeVee. For energies below 1 MeVee down to ∼100 keVee a closer approximation of the expected FoM for SNM can be attained when using 252Cf as a proxy source or by utilising an ‘enhanced’ AmBe source with the addition of a further low energy γ ray source.

Highlights

The use of neutron discriminating plastic scintillators, such as the material produced by Eljen [1, 2], coupled with a silicon photomultiplier (SiPM) readout has become increasingly commonplace in detection of special nuclear materials (SNM)
In this work we study the neutron/gamma pulse shape discrimination (PSD) properties of a plastic scintillator-SiPM system [7, 8] to assess the suitability of various radionuclide neutron sources as proxy sources for SNM
We have shown in this work the functionality of a compact neutron-γ discriminating detector for use in detecting SNM

Summary

Introduction

The use of neutron discriminating plastic scintillators, such as the material produced by Eljen (most recently as EJ-276) [1, 2], coupled with a silicon photomultiplier (SiPM) readout has become increasingly commonplace in detection of special nuclear materials (SNM).In this work we study the neutron/gamma pulse shape discrimination (PSD) properties of a plastic scintillator-SiPM system [7, 8] to assess the suitability of various radionuclide neutron sources as proxy sources for SNM. In order to assess a system’s ability to identify SNM, it is often useful to use ‘proxy’ sources where a sample of SNM may not otherwise be available, namely 252Cf [15,16,17], or one of the previously mentioned (α,n) sources. In these cases one must carefully consider the respective differences between the sources, namely, the energies of emission, and the multiplicities of those emitted particles. We report a comparative study of the performance of a PSD plastic scintillator using two different radionuclide neutron sources 241AmBe and 252Cf plus a sample of weapons-grade plutonium (

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