Advancements in Gd-based neutron detection (2): Proton–gamma correlation approach

Abstract

The paper introduces new developments in the conception, optimization, and principle validation of a neutron counter, based on the insertion of gadolinium in plastic scintillators, that is under work at CEA LIST since 2017. The radiation sensor, comprising two volumes of scintillating polymers, it is, by nature, sensitive to both neutron and gamma radiations. This allows the design of a versatile n/γ detector, provided that it is possible to algorithmically separate the signature of both types of radiations. After amplitude and gamma–gamma coincidence filtering, the authors investigate a third n/γ discrimination mode by proton–gamma temporal correlation filtering. After a bibliographic study, the article details the estimation of the temporal parameter useful for such a discrimination, firstly by explicit calculations, secondly by means of a MCNP6.1-based, dedicated simulator. A time-based-processing firmware, embedded into a pulse acquisition card, was then created to compare these estimates with experimental distributions. A 50-μs temporal gate was identified as relevant to discriminate temporal correlations in presence of a neutron emitter. A compensation technique was eventually implemented in order to obtain first experimental estimates of neutron sensitivity, and neutron detections limits in a mixed field. The study ends up providing a maximum reachable sensitivity in the order of 0.3 c.n−1.cm 2 under a fast neutron flux (AmBe), with two 1-L plastic scintillators separated by a 250-μm Gd converter, and the associated temporal correlation and compensation algorithm, as well as neutron detection limits in the same order as those of a He-3 Bonner sphere over acquisition times between 1 and 10 min.