Quantitative gamma-spectrometry of nuclear material under conditions of limited information about assayed objects

Canberra Industries has developed a specialized software package, Advanced In-Situ Object Counting System (A-ISOCS), which is based on absolute gamma-spectrometric measurements. It is intended for the verification of the quantity of nuclear materials under conditions where measurements are challenged by incomplete information on the properties of assayed objects which are inspected by the International Atomic Energy (IAEA)'s inspectors. A-ISOCS introduces a technique, which is called the automated optimization that allows the users to determine unknown sample parameters as well as the mass and isotopic composition of nuclear materials. The optimization process is carried out by using benchmarks referring the information included within the gamma-ray spectrum of the measured item. For each benchmark, Figure-of-Merit (FOM) is calculated and used to find the most consistent quantitative result (the best solution) corresponded to the minimized FOM. We have evaluated the capabilities and performance of A-ISOCS based on the measurements of uranium standard reference material samples, which have well-known geometry parameters and physical properties. In addition the applicability of the software to field measurements was assessed with an extensive set of gamma-ray spectra from holdup materials collected at uranium bulk handling facilities. This paper summarizes the results of our evaluation activity.