Accuracy of Uranium Isotope Analysis in Microparticles by Secondary Ion Mass Spectrometry

The results of measurements of ²³⁵U/²³⁸U isotope ratios in microparticles of a reference material performed by Cameca IMS-4f and Cameca IMS 1280-HR mass spectrometers are compared. Twenty-eight particles of various shapes and sizes and also one spherical uranium oxide particle approximately 0.6 μ in size were analyzed by both instruments. These particles were selected based on a preliminary SEM–EDX analysis. The results indicate that the Cameca IMS-1280 HR mass spectrometer can measure uranium isotope ratios with precision up to thousandths of percent, while the Cameca IMS-4f mass spectrometer can measure only up to tenths of percent. For measurements of uranium-235 concentrations at the 0.7% level, the error range for mass spectrometers with a “large” magnet is two orders of magnitude smaller than the errors from mass spectrometers with a “small” magnet, with measurement errors more than ten times lower. Additionally, while mass spectrometers with a small magnet cannot measure minor isotope concentrations at the 5 × 10^–3% level in submicrometer particles, mass spectrometers with a large magnet can achieve this with an error of less than 10%.