Virtual Gamma-ray Spectrometry for Template-Matching Nuclear Warhead Verification

Gamma-ray spectrometry has been successfully employed to identify unique items containing special nuclear materials using both attribute and template approaches. Based on an analysis of measured gamma spectra, attribute measurements determine selected characteristics of the item (e.g. an isotopic ratio or a minimum mass); template measurements compare the spectrum against a “template” that has been previously generated with a trusted reference item. High-resolution (HPGe) detectors are essential, in particular, for attribute measurements in order to resolve isotopic-specific features in the spectra. In this analysis, we use the Monte Carlo particle transport code MCNP to model simple material-detector configurations. We examine a series of basic diversion scenarios and assess the viability of gamma-ray spectrometry for verification applications. We examine, in particular, also the use of low-resolution (sodium-iodide scintillation) detectors for this purpose: these detectors are inadequate for attribute-measurements, but—depending on the requirements—may be viable for template systems. The lack of detail in the data acquired with these detectors may help protect classified information or reduce the requirements for information barriers.