Fast neutron spectrometer composed of PSPCs and Si(Li)-SSDs with excellent energy resolution and detection efficiency

We have developed a fast neutron spectrometer composed of three position-sensitive proportional counters (PSPCs) with methane gas and two Si(Li) surface barrier semiconductor detectors (SSDs). A collimated incident neutron beam interacts with hydrogen atoms in the methane gas to generate recoil protons. Position information of the recoil protons obtained from the PSPCs gives the recoil angle. At the same time, the energy of the recoil protons is measured with the three PSPCs and the two SSDs. Finally, the neutron energy is derived using the recoil-proton energy and the recoil angle. This spectrometer was experimentally tested using a monoenergetic neutron beam with energy of 5.0 MeV. The energy resolution and the detection efficiency were 3.5% and 1.1 times10^-3 %, respectively. The energy resolution could be achieved better than 2% by selecting events under proper conditions. We also developed a Monte Carlo code to evaluate the characteristics of the spectrometer. The results obtained from these simulations are compared to those obtained through experiments