To address the problem of the shortage of neutron detectors used in radiation portal monitors （RPMs）, caused by the 3He supply crisis, research on a cadmium-based capture-gated fast neutron detector is presented in this paper. The detector is composed of many 1 cm × 1 cm × 20 cm plastic scintillator cuboids covered by 0.1 mm thick film of cadmium. The detector uses cadmium to absorb thermal neutrons and produce capture 7-rays to indicate the detection of neutrons, and uses plastic scintillator to moderate neutrons and register y-rays. This design removes the volume competing relationship in traditional 3He counter-based fast neutron detectors, which hinders enhancement of the neutron detection efficiency. Detection efficiency of 21.66% ×1.22% has been achieved with a 40.4 cm× 40.4 cm × 20 cm overall detector volume. This detector can measure both neutrons and T-rays simultaneously. A small detector （20.2 cm × 20.2 cm × 20 cm） demonstrated a 3.3 % false alarm rate for a 252Cf source with a neutron yield of 1841 n/s from 50 cm away within 15 s measurement time. It also demonstrated a very low （〈0.06%） false alarm rate for a 3.21 × 10^5 Bq 137Cs source. This detector offers a potential single-detector replacement for both neutron and the y-ray detectors in RPM systems.
In this paper, the detection efficiency of a large area neutron sensitive microchannel plate detector has been evaluated. A ^6LiF/ZnS scintillator detector 65 mm in diameter and 0.32 mm in thickness, with product code,EJ426HD2, produced by Eljen Technology, was employed as the benchmark detector. The TOF spectra of these two detectors were simultaneously measured and the energy spectra were then deduced to calculate the detection efficiency curve of the ^nMCP detector. Tests show the detection efficiency@25.3 me V thermal neutrons is 34% for this ^nMCP detector.
