A novel method for trace uranium determination in plutonium by thermal ionisation mass spectrometry

An isotope dilution -thermal ionisation mass spectrometric (ID-TIMS) methodology using enriched 235 U (>90 at.%) as a spike is described for the determination of trace uranium (U) in plutonium (Pu). The method is based on the monitoring of UO+ instead of U+ in order to overcome the isobaric interference of 231 Pu at 231 U. The present approach obviates the need for the chemical separation of microgram quantities of U from relatively large amounts of Pu. This method is useful for determining decontamination factors during U-Pu chemical separation, and also for determining trace U in a proposed Pu chemical assay reference material. In practice, the U isotopic concentration in the Pu sample must be known for highly accurate results. (C) 2007 Elsevier B.V. All rights reserved.