Gamma-Ray Rejection of the SiPM-coupled Micro-Layered Fast-Neutron Detector

The Micro-Layered Fast-Neutron Detector (MLFD) is a proton-recoil fast-neutron scintillator that uses lucite as the hydrogen-rich neutron converter and silver-doped zinc sulfide (ZnS:Ag) as the inorganic scintillator medium. The MLFD is constructed by placing alternative layers of neutron converter and scintillation medium in order to maximize its light collection. A 43-mm long MLFD has previously shown a high detection efficiency of 9.2% for a bare
²⁵²
Cf source, and exhibits acceptable gamma-ray suppression with pulse height discrimination. Pulse-shape discrimination of neutrons and gamma-rays yielded a figure-of-merit of 4.56. Modeling in Geant4 has shown that lengthening the MLFDs up to 200 mm can further increase the neutron detection efficiency. These results indicate that the MLFD can potentially be used in applications such as active and passive interrogation, and Special Nuclear Material (SNM) searches. However, the light collection device used thus far has been photomultiplier tubes (PMTs), which prove to be infeasible at longer lengths of the MLFD. To construct a compact hand-held neutron detection system, the PMTs would require to be replaced with silicon photomultipliers (SiPMs). Thus, this paper reports the performance of the MLFD coupled to SiPMs when irradiated with neutrons and gamma-rays. The results show that the MLFD-SiPM system is highly insensitive to gamma-rays (pulses not discernible from electronic noise), and simply setting a threshold to reject electronic noise is sufficient to register only neutron events. This indicates that the MLFD-SiPM system would be a compact, highly efficient fast-neutron detector in a gamma-ray environment.