SUMMARY

The purpose of this research is to determine the feasibility of creating an energy-dependent neutron detector array that could be used to detect special nuclear materials. The proposed detector array is composed of idealized thermal neutron detectors covered by moderators of differing size, namely thickness and shape. Through a series of Monte Carlo radiation transport calculations, the size, shape, and location of the moderators and detectors will be optimized to determine the efficacy of obtaining a neutron energy spectrum measurement in a single counting event, i.e. a single measurement. This approach expands on the concepts of the Bonner Sphere Spectrometer (BSS) which relies on multiple measurements using differing size moderating spheres. Although a proven approach, the traditional BSS method is not practicable for several applications. An alternative approach to the spectrum measurement is the use of detector sums or ratios to distinguish fission neutron spectra from other neutron spectra that might be encountered. The resulting system should be capable of being vehicle mounted so it would be mobile.