Effects of neutron source selection on land-mine detection efficiency

Abstract

One proposed method of land-mine detection is based on measurements of the 10.8 MeV photons from the 14N(n, γ) reaction. In this study, simulations of the photon production efficiencies for nitrogenous explosive material (TNT), buried in soil having variable moisture content, were completed for different published neutron spectra. Monte Carlo simulations were performed with MCNP with a cylindrical geometry of TNT considered as target material and with neutron energies ranging from thermal to 20 MeV. The numbers of 14N(n, γ) reactions in TNT were tallied to obtain response functions. To find the effectiveness of different neutron sources, response functions were folded with the neutron spectra. Response curves reveal that higher water content increases response for fast neutrons, and reduces response for slow neutrons. Lower energy neutron sources, i.e. D(d, n) or 252Cf, are more suitable than higher energy neutron sources such as 241Am–Be or T(d, n). Although its advantages disappear with increasing depth, the usage of moderating spheres of CH 2 increases the signal significantly when compared with a bare source, while also reducing neutron dose to workers.