Study on Effect and Solving Method of Polyatomic Ion in Isotopic Ratio Analysis of Uranium Bearing Particle in SIMS

The matrix composition of the actual environmental samples is very complex, and the effect of polyatomic ion on the uranium isotope ratio analysis of SIMS individual particle cannot be ignored. The effects of polyatomic ion of Pb, Ni, Zn and Si on the uranium isotope ratio analysis of SIMS individual particle were analyzed in the experiment, and the results were corrected by improving the mass resolution, or subtracting the polyatomic ion according to the ion intensity of the nuclide. The results show that the polyatomic ion of Pb and Ni can affect the minor isotopic ratio analysis of uranium bearing particles, and the effect on the major isotopic ratio analysis can be ignored. The polyatomic ion of Zn and Si has no effect on the measurement of uranium major and minor isotope ratios basically. After increasing mass resolution to 800, the effect of polyatomic ion of Ni can be completely eliminated. For NiCRM U030 mixture particles, the measurement error of ²³⁴U/²³⁸U is better than 5% basically, and that of ²³⁶U/²³⁸U is better than 15% basically. The effect of polyatomic ion of Pb cannot be eliminated by increasing mass resolution. After deducting its polyatomic ion according to the intensity of Pb⁺, for Pb-CRM U030 mixture particles, the measurement error of ²³⁴U/²³⁸U is better than 10% basically, and the measurement error of ²³⁶U/²³⁸U is better than 50% basically. The method was applied to real sample analysis, and the results show that the effect caused by polyatomic ion is effectively eliminated.