Application of stilbene crystals in neutron measurement for monoenergetic neutron beam

Abstract

Stilbene crystals are used as neutron detectors connected with photomultiplier tubes. An online acquisition method assembled by CAMAC standard plug-ins, NIM plug-ins, a neutron-γ (n-γ) discrimination plug-in named Canberra-2160A, and an offline acquisition method, assembled with an oscilloscope, were developed to obtain nuclear signals from neutron detectors. The online and offline acquisition methods collected pulse signals simultaneously while n-γ discrimination and measurement of deuterium-deuterium (DD) and deuterium-tritium (DT) neutron beam were carried out by both acquisition methods. The resulting n-γ discrimination, detection efficiency, and neutron spectra of varying stilbene crystal sizes were obtained. The neutron events accounted for approximately 80% of the total events in this radiation field formed by DD neutron beam and 50% for DT neutron beam. The results of n-γ discrimination of the two acquisition methods matched very well. The figures of merit (FoM) of n-γ discrimination obtained by the online acquisition method were 2.158 for the radiation field formed by DD neutron beam and 1.802 for DT when over 105 pulses were used for analysis. The pulses acquired by the offline acquisition method were repeatedly used to obtain the best discrimination effects, neutron charge-amplitude spectrum, and pulse height spectrum after the particular waveform digitization process. It was shown that the offline acquisition method composed of stilbene crystals, a photomultiplier tube, and a digital oscilloscope could realize the same function and effect as the online acquisition method for monoenergetic neutron beam, but with fewer pulses. A feasible experimental method was obtained which have a good potential for the neutron flux monitoring of the pulsed-neutron radiation fields, in which the total number of events is small or the neutron propagation process is instantaneous.