Nuclear Forensics: Measurements of Uranium Oxides Using Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS)

摘要

Over the past decade, law enforcement, governmental and public agencies have been stymied by the threat of the trafficking of nuclear materials. During this time span, reports from the International Atomic Energy Agency of illicit trafficking have increased eightfold from 20 to 160. For this reason, nuclear forensics is a burgeoning science focused on the identification of seized special nuclear materials. Identification of these materials is based upon the wealth of information that can be obtained by applying multiple analytical and measurement technologies. All of the information gained from each sample can then be used to further characterize other samples culminating in the inclusion of all of the collected data into a central database. Information must be reported in a timely manner as actionable results need to be presented as quickly as possible if there is to be any attribution for trafficking of nuclear material. Identification parameters such as uranium content, isotopic composition, and levels of impurities can be measured simultaneously in an effort to completely characterize a sample. All of these measurements combined can offer information as to the source of the material and its intended use. Many of the current analytical techniques used in nuclear forensics require extensive sample preparation and offer minimal amounts of information about the sample. Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) is presented as a rapid analytical technique that provides many of these identification parameters with minimal sample preparation. TOF-SIMS spectra were collected on eight different standard reference materials covering a range of stoichiometries and levels of enrichment. Samples included UO2, UO3 and U3O8 stoichiometries ranging from slightly depleted (0.5% 235U) to highly enriched (90.0% 235U) uranium.