Year
2012
Abstract
The K-Edge Densitometer (KED) is a ubiquitous and reliable instrument for nuclear safeguards, and has been used in analytical laboratories for more than 30 years. During that time, K-Edge densitometry has been applied in stand-alone KED systems and Hybrid K-Edge/xrf Densitometer (HKED) systems to rapidly measure the concentration of one or more actinides in a liquid sample. In safeguards applications of the KED technique, each specimen consists of several milliliters of liquid, contained in a sample vial. In traditional KED analysis, the actinide content is derived using an actinide-free blank specimen as the basis for comparison with an unknown specimen. In this paper, the underlying equations of traditional K-Edge Densitometry are approached from a revised perspective, and a new analytical mode for the KED instrument is derived. This approach was named Actinide Density-Difference Mode (ADDM) analysis by the author. In ADDM analysis, no actinide-free reference sample (such as blank nitric acid) is required. An actinide-bearing calibration standard, similar in overall composition to the unknown, serves as the basis for comparison with the unknown sample. The results of ADDM are derived from observed count rates, rather than from measurements of absolute transmission. Because count rates (rather than transmission values) are the basis of ADDM calculations, this approach is well suited for continuous realtime monitoring applications. The analytical result of ADDM is the observed difference in areal density (for each actinide of interest) between the unknown sample and the calibration sample, as a function of time. Potential safeguards applications of the ADDM technique are described. A recommended application of ADDM involves the continuous on-line measurement of materials that pass through a fixed measurement station, such as a pipe inside a reprocessing plant.