A Monte Carlo Study of Contraband Detection Using Fast Neutron Resonance Technique

摘要

Fast neutron resonance technique was simulated using MCNP-4C (Monte Carlo N-Particle System) to find its usefulness to contraband inspection. By applying neutron techniques, elemental composition of the material in question can be characterized, by which existence of explosives or narcotics are recognized among many other stuffs being investigated. To obtain fast neutron flux, D(d,n)~3He reaction was chosen and using a computer code, DROSG-2000, we produced the flux with variables of energy and neutron radiating angle. Neutron energy range of 2.25 to 5.25 MeV, which includes apparent resonance peaks for carbon, oxygen and nitrogen, was applied to the simulation. By moving around the neutron source, a set of a material to be investigated and neutron detector experiences neutrons in the form of narrow line beam with different energies as the angle to the neutron source changes. By positioning the set of the material and detector at several angles, we can obtain the equal number of linear equations to solve as the number of applied angles. Total attenuation of neutron flux obtained at different angles was calculated by using the results of MCNP-4C simulation cases. Among many trials with different number of energy range segmentations and number of element in the material in question, feasible results could be found when the number of elements was five and energy bin was five to nine. More cases when the material in question was mixed or covered with interfering elements such as Al, Ni, Cr, Mn, Fe and Si were also simulated to show the increase of relative error up to 50 %. More studies to decrease the size of error occurring when the material in question exists with interfering elements and the effects of applying broad beam to the system are required.