Best practices for determining uranium isotopic composition by MGAU and FRAM

Abstract

MGAU and FRAM are software codes which can be used for determining uranium isotopic composition by gamma spectrometry. The aim of this study is to establish best practices for using these codes to obtain the results as accurate as possible under given constraints. Uranium measurements can take place either in a laboratory (under optimal conditions) or in field (under non-optimal conditions). Both scenarios were investigated in this work. There are several factors affecting accuracy of analysis results. Some of the factors cannot be controlled. However, there are crucial factors that can be controlled such as the sample-to-detector distance and acquisition time. These two particular factors were studied. The study was based on using gamma-ray uranium spectra generated from real spectra of various certified materials and well characterized fuel pellets. The spectra were generated by Cambio software. This software randomly samples data from a real spectrum and allows generating "daughter spectra" having different number of total counts. This way enough statistically relevant data can be obtained. More than 10 000 spectra have been used in this study. This study also discusses influence of bismuth on the accuracy of MGAU and FRAM. The results of this work can help inspectors and analysts to appropriately set up gamma-spectrometric measurements of the uranium isotopic composition.