A scintillating plastic fiber array and multiplexer based 384-channel fast neutron spectrometer.

A fast neutron detection system based on a scintillating plastic fiber array and multiplexer was designed to measure the spectrum of fast neutrons ranged 10 MeV-100 MeV. With the method of nuclear recoil, the energy of incident neutron was determined by measuring the recoil proton track and deposited energy in scintillating plastic fibers. The detection system was composed of a scintillating plastic fiber array, 6 position sensitive photomultiplier tubes, and a high-density readout electronics based on the multiplexer. The scintillating plastic fiber array was made as a staggered structure with two kinds of fibers in different sizes (0.5 mm-square fiber and 3 mm-square fiber). The structure provided a wider detection energy range and better detection efficiency than arrays made with uniform plastic fibers. A dedicated digital electronics system was well designed to control the whole readout system to provide 384-channel signal processing. The detector had a 48 mm × 48 mm effective detection area and a mechanical size of 34 cm × 34 cm × 27 cm. In the simulation of the detector model performance, the system gave an energy resolution of 23%-35% for neutrons ranged 10 MeV-100 MeV. Experimental results showed that the detector had a good energy linearity and energy resolutions were, respectively, 35.82% at 14.817 MeV, 36.84% at 21.264 MeV, 35.90% at 23.069 MeV, and 32.90% at 24.220 MeV. The optimized prototype model had potential in increasing fast neutron detection performance.