Round robin for uranium isotopic measurements by mass spectrometry

A round-robin for uranium isotopic analysis in two solutions with different concentrations prepared and certified by the Institute for Reference Materials and Measurements (IRMM, Geel, Belgium) was organized by CETAMA, a division of the Commissariat à l’énergie Atomique (CEA: French Atomic Energy Commission Fourteen laboratories took part in the program using twenty-five different instruments (ICP-QMS, ICP-SFMS and TIMS). For each solution and each isotopic ratio, a statistical analysis based on standard ISO 5725 was carried out to calculate the mean, the repeatability and reproducibility standard deviations, the z-score and zeta-score, the bias with respect to the target values, and to compare their precision. The mean measurement results for the ²³⁴U/²³⁸U and ²³⁵U/²³⁸U isotopic ratios show no significant biases compared with the target values, whatever is the analytical technique. The results were much less satisfactory for the ²³⁶U/²³⁸U isotopic ratio, for which only the laboratories specialized in traces analyses and/or precise isotopic analyses submitted results in good agreement with the target values. A detailed discussion is given in this article.