Applications of gamma-ray spectrometry in the quantitative nondestructive assay of special nuclear materials

Nearly all applications of gamma-ray spectrometry in the quantitative assay of special nuclear materials can be grouped into five general categories. They are as follows: 1) quantitative passive assay, of which transmission-corrected passive assay methods for measuring isotopic masses/concentrations are an important subset; 2) enrichment measurements on ''infinitely thick'' samples for the absolute determination of isotopic fractions/concentrations; 3) measurements of isotopic ratios using relative detection efficiency principles resulting in absolute isotopic distributions without recourse to standards; 4) absorption-edge densitometry measurements of elemental concentrations; and 5) X-ray fluorescence measurements of elemental concentrations. Careful and correct practice of these techniques can yield measurement accuracies in the range of 0.1-1.0% in favorable situations with measurement times generally in the range of 15 min to 1 h. We present examples of these general categories with emphasis on those measurements and techniques exhibiting the best accuracy, as well as those which are not routinely practiced in many other applications of gamma-ray spectrometry. (orig.)