Abstract
The accuracy and precision of isotope amount ratio measurements using thermal ionization mass spectrometry (TIMS) instrumentation are described, and the measurement of Pu materials is emphasized. The mass fractionation observed for Am, Ga, Pu, and U for isotope amount ratio measurements using the total evaporation (TE) technique is compared with theoretical estimates to demonstrate the advantage of the TE methodology and to investigate systematic biases in the major isotope amount ratios of U and Pu certified reference material (CRM) standards from the U.S. provider of CRMs. The quality of the Pu isotopic data generated by TIMS instruments in an analytical laboratory is demonstrated by the application of the double ratio technique to estimate the 241Pu half-life. Analytical data on traceable Pu CRMs from the New Brunswick Laboratory (NBL), generated as part of routine measurements supporting various programs, are used for this half-life estimation. Although the 241Pu abundances in CRMs of 136, 137, 138, and 126-A are approximately 200-2000× smaller than those in the 241Pu material used in the previous Institute for Reference Materials and Measurements (IRMM) evaluation of the 241Pu half-life, the half-life value estimated in this work shows excellent agreement with the currently accepted value from the IRMM. This agreement also demonstrates the pedigree of the Pu isotopic standards from the NBL and the quality of the isotope amount ratio measurements using TIMS instrumentation. For both the major and minor Pu isotope amount ratios, this report describes the relative importance of the factors affecting the uncertainty of TIMS measurements, which are considered the gold standard in isotope ratio measurements (LA-UR-24-29199).
| Original language | English |
|---|---|
| Pages (from-to) | 1879-1901 |
| Number of pages | 23 |
| Journal | Journal of Analytical Atomic Spectrometry |
| Volume | 40 |
| Issue number | 8 |
| DOIs | |
| State | Published - Jul 30 2025 |
Funding
I thank colleagues in nuclear safeguards organizations within the U.S. and outside the U.S. with whom I was privileged to interact with during my career at the NBL, Savannah River National Laboratory (SRNL), and LANL. I also thank the leadership teams at NBL (Jon Neuhoff, Usha Narayanan, Colleen Gradle, Richard Essex, Chino Srinivasan, and Pete Mason), SRNL (M. Holland and M. Brisson), and LANL (Steve Willson and Lav Tandon) for their encouragement and support. Discussions on uncertainty estimation techniques, metrology concepts, and QC aspects of isotope amount ratio measurements using TIMS instrumentation with the above personnel and with Stephan Bürger, Stephan Vogt, and Steve Balsley (IAEA), Stephan Richter (JRC-Geel), Cole Hexel (ORNL), Will Guthrie and Rudiger Kessel (NIST) are greatly appreciated. LANL colleagues Nick Butterfield, Russ Keller, and Chelsea Ottenfeld are thanked for their help with analytical tasks. Constructive reviews from two anonymous reviewers are acknowledged.