Transmission measurement correction for self-attenuation in gamma-ray assays of special nuclear materials

The central and most difficult problem in the NDA of bulk samples by passive gamma-ray spectroscopy is the correction of the sample self-attenuation. Because of the severity of the problems in many plutonium and uranium samples, the usual calibration and attenuation correction methods involving direct comparison to standards or exploitation of prior knowledge of chemical composition are often not applicable. Determination of the sample linear attenuation coefficient (μ) by a separate transmission measurement with an external source has proven to be the most generally useful procedure. This paper reviews the various procedures in use and presents results of a study of the transmission method of attenuation correction applied to the most important geometrical classes of assay samples, namely box-shaped and cylindrically shaped samples. These classes include most of the large array of vials, bottles, cartons, boxes, cans, drums, crates, and barrels used for storing SNM. 6 fig