Abstract

Isotopic analysis of ultra-trace uranium particles for nuclear safeguards requires the highest level of accuracy and reliability. Previously, uranium isotope ratios in NUSIMEP-7 (the 7th Nuclear Signatures Interlaboratory Measurement Evalua- tion Programme; an interlaboratory comparison/proficiency-test exercise for uranium microparticles) particles were determined using thermal ionization mass spectrometry (TIMS) with an optimized static detection method, yielding satisfactory results. However, the data integration procedure can also significantly influence the final analytical results, especially for ultra-trace level samples analyzed by the continuous heating method. In this study, raw data from the original NUSIMEP-7 particle analysis were retrospectively re-processed using a recently optimized data integration protocol: ‘Method I’ (Summed Intensity Ratio), with an ‘over 25%’ signal integration range. The results showed improvements in accuracy for all isotope ratios. Most notably, the z-scores and zeta-scores, which are critical for interlaboratory comparison programs, were significantly improved, moving from ‘acceptable’ or ‘warning’ levels to ‘excellent’. For the key n( 235 U)/n( 238 U) ratio, the z-score improved from 1.9 to -0.66, and the zeta-score improved from 1.3 to -0.12. This study demonstrates that applying optimized data processing protocols, even retrospectively, can significantly enhance the fidelity and reliability of ultra-trace isotopic analyses.