Direct uranium isotope ratio analysis of single micrometer-sized glass particles

摘要

We present the application of nanosecond laser ablation (LA) coupled to a ‘Nu Plasma HR’ multi collector inductively coupled plasma mass spectrometer (MC-ICP-MS) for the direct analysis of U isotope ratios in single, 10–20 μm-sized, U-doped glass particles. Method development included studies with respect to (1) external correction of the measured U isotope ratios in glass particles, (2) the applied laser ablation carrier gas (i.e. Ar versus He) and (3) the accurate determination of lower abundant ²³⁶U/²³⁸U isotope ratios (i.e. 10⁻⁵). In addition, a data processing procedure was developed for evaluation of transient signals, which is of potential use for routine application of the developed method. We demonstrate that the developed method is reliable and well suited for determining U isotope ratios of individual particles. Analyses of twenty-eight S1 glass particles, measured under optimized conditions, yielded average biases of less than 0.6% from the certified values for ²³⁴U/²³⁸U and ²³⁵U/²³⁸U ratios. Experimental results obtained for ²³⁶U/²³⁸U isotope ratios deviated by less than −2.5% from the certified values. Expanded relative total combined standard uncertainties Uc (k = 2) of 2.6%, 1.4% and 5.8% were calculated for ²³⁴U/²³⁸U, ²³⁵U/²³⁸U and ²³⁶U/²³⁸U, respectively.