Computational Study of a Small Size Neutron Moderator for Use on Neutron Dosemeters Based on Silicon Diodes

A small size polyethylene moderator for use on neutron dosemeters based on silicon diodes has been studied using the MCNP-4A code to determine the size and geometry that allow an improvement to the dosimeter's response for neutrons in the energy range 10 keV - 1 MeV. Various dimensions of cylindrical and spherical moderators with or without a central cylindrical opening have been modelled for 1 MeV starting neutrons at normal incidence on the detector area. Since silicon diodes provided with a borate polyethylene converter allow thermal and fast neutron detection, the number of fast and thermalized neutrons reaching the detection area is observed as a function of the detector positioning inside the moderator for each geometry considered and compared with results obtained for Bonner Spheres. The evolution in the number of thermalized neutrons with starting neutron energy is shown for some of the geometries and a moderator with a natural boron absorber layer is proposed. (author)