Evaluation for gamma-ray rejection ability affecting neutron discrimination property in scintillating-fiber type of fast neutron detector

摘要

Scintillating-fiber (Sci-Fi) detector has been employed to measure 14 MeV neutrons in the magnetic confinement fusion experiment. Design of the Sci-Fi detector reduces response to gamma-rays, compared to bulk scintillators, while at the same time enabling directional responses to energetic neutrons. Ability of gamma-ray rejection is an important parameter to judge the discrimination property for a fast neutron detector. In order to investigate the gamma-ray rejection abilities in the case of 2.45 MeV neutron and higher-energy neutrons, the pulse height spectra (PHS) of four different-head detectors in different diameter and with/without the aluminum (Al) matrix have been measured by using the accelerator-based neutron source with d-D reaction. Four different-head detectors show the different pulse height properties and the gamma-ray rejection abilities, which impact upon the neutron discrimination abilities. Meanwhile, simulations of detector responses have been performed using the Particle and Heavy Ion Transport code System (PHITS) to analyze the experimental results. Neutron discrimination abilities of small diameter Sci-Fi is better than that of large diameter Sci-Fi. Al matrix is beneficial to enhance 6.6-10 times difference of the gamma-ray rejection affecting the neutron discrimination ability in the case of Sci-Fi with/without Al matrix. It is also found that the neutron discrimination abilities of the Sci-Fi without the Al matrix and a plastic scintillator are the same.