Direct isotope ratio analysis of individual uranium–plutonium mixed particles with various U/Pu ratios by thermal ionization mass spectrometry

Uranium and plutonium isotope ratios in individual uranium–plutonium (U–Pu) mixed particles with various U/Pu atomic ratios were analyzed without prior chemical separation by thermal ionization mass spectrometry (TIMS). Prior to measurement, micron-sized particles with U/Pu ratios of 1, 5, 10, 18, and 70 were produced from uranium and plutonium certified reference materials. In the TIMS analysis, the peaks of americium, plutonium, and uranium ion signals were successfully separated by continuously increasing the evaporation filament current. Consequently, the uranium and plutonium isotope ratios, except the ²³⁸Pu/²³⁹Pu ratio, were successfully determined for the particles at all U/Pu ratios. This indicates that TIMS direct analysis allows for the measurement of individual U–Pu mixed particles without prior chemical separation. - Highlights: • U–Pu mixed particles with U/Pu ratios of 1, 5, 10, 18 and 70 were produced. • U and Pu isotope ratios were determined by TIMS for particles without prior chemical separation. • Accurate values were obtained for all isotope ratios, except the ²³⁸Pu/²³⁹Pu ratio