Calculation of Neutron Yields Released by Electrons Incident on Selected Materials

Abstract

Calculations are described of yields of low-energy neutrons released by electrons incident on semi-infinite slabs of natural C, Al, Fe, Ni, Cu, Ag, Ba, Ta, W, Au, Pb and U, for all incident electron energies. Yields are based on photon differential track length distributions derived for thick targets from Approximation B of analytical shower theory, with additional corrections for electron and photon propagation in the materials. The track length distributions are folded together with published photoneutron cross sections by numerical integration. When referred to unit incident electron beam power, the yield of each material exhibits a sigmoid behavior, rising from threshold to approach a constant saturation value. At high electron energies, the average trend of the neutron yield is given by 9.3 × 1010 Z(0.73±0.05) neutrons sec−1 kW−1. Quantitative comparison is made to yields obtained in a separate calculation in which Approximation A is substituted for Approximation B. Comparison is made to published calculations and measurements, and radiation protection implications are discussed.