Parametric Study of Design Characteristics for Neutron Interrogation of Materials by Analysis of Gamma Spectrum

Author(s):

Nusrat Sarwahrdy, Ryan Brockington, Jason Barbier, and Marc Litz

Abstract:

The technique of neutron interrogation of materials enables a description of the elemental composition of soil and its components. Neutrons from an electronic neutron generator interact with atomic nuclei causing the production of characteristic gamma rays that identify the composition of a material volume. Determination of the elemental composition has wide-ranging applications in environmental science, planetary science, and lunar science. Detection of nitrogen-based explosives is crucial to Soldier safety. NASA has determined the chemical composition of lunar and planetary soil for use in understanding the development of the solar system. Simulation geometries and material composition within Monte Carlo N-Particle Transport are varied. The simulation geometry (source, shield, target, and detector) is optimized to maximize photon flux in the detector as well as maximize neutron flux in target. The depth of the target in soil is varied and quantified. The neutron flux in the target volume varies 93% over a 2-ft depth. A parametric study of detector height above the soil found that 10 cm maximizes photon flux. A 28-cm shielding radius resulted in 90% reduction of neutron flux in cerium(III) bromide (CeBr₃). Prominent energies in gamma spectrum in CeBr3 detector are identified.