Experimental evaluation of the detection methods of thermal ionization mass spectrometry for isotopic analysis of ultra-trace level uranium

Thermal ionization mass spectrometry (TIMS)-based isotopic analysis of various amounts of uranium was performed to experimentally evaluate three detection methods: multi-dynamic, dynamic, and static. The analytical performances of the detection methods in terms of accuracy, precision, and measurement uncertainty were not significantly different for the analysis of 1 ng and 100 pg of uranium, whereas using ion counters for detecting ²³⁸U⁺ signal intensity slightly enhanced the performance for analyzing 30 pg of uranium. The static detection method improves the analysis performance for 5 pg and 1 pg of uranium due to the higher detection sensitivity of ion counters than faraday cups, elimination of ion signal drift, and increased number of valid data sets in a measurement. The experimental evaluation of the detection methods provides a basis for optimizing the detector configuration of TIMS in terms of the amount of uranium in samples. The uranium isotope ratios in microparticles measured by the static method agreed well with the certified values; this verified the applicability of the static detection method to particle analysis of environmental samples required for nuclear safeguards.