Simulations of neutron response and background rejection for a scintillating-fiber detector

Abstract

We address the problem of detection of fast neutrons at energies of 5–30 MeV in the presence of strong backgrounds of low-energy neutrons and gammas. In an organic scintillator, the neutrons are detected mainly as recoil protons from n-p scattering; the gammas produce electrons primarily by Compton scattering. The recoil protons and electrons can be distinguished because the light output per unit distance near the end of a proton track is much higher than that for an electron. This difference could be used to reject gamma backgrounds such as those in a reactor environment by constructing a segmented detector from a bundle of scintillating fibers connected to a readout device. We present the results of extensive simulations for a module composed of 6400 fibers, each 250 μm square, arranged into a 2×2×2 cm 3 bundle. Considered were fast neutrons with energies of 3, 7, 14 and 28 MeV and backgrounds composed of neutrons and gammas with energy distributions characteristic of delayed emission from a fission source. The simulations indicate that the detector can obtain a good compromise between outstanding background rejection and reasonable detection efficiency for the neutrons of interest.