Response functions of spherically moderated neutron detectors

Abstract

This paper presents the results of Monte Carlo calculations on the response functions of spherical moderator-detector systems as a function of neutron energy in the energy range from 10⁻⁷-14 MeV. The diameter of the polyethylene moderator varied in the range of 2 inch to 12 inches and the central thermal neutron detectors considered were LiI scintillators and BF₃ counters of varying diameters. The best microscopic cross section data available in the literature was used for all the constituents of the moderator and of detectors. Anisotropy of neutron scattering was taken into account. Variations in all neutron response due to change of thermal neutron detector size or the detector material itself as well as due to the presence of an annular air gap surrounding the thermal neutron detector were studied. The air gap reduces the sensitivity of the system to neutrons but the nature of the energy response curve is not affected. Computed response functions of the rem counter devised by J.W. Leake of Harwell are also presented.