Results of an international trial comparison of activity measurements of a solution of 192Ir

Ten laboratories took part in a trial international comparison of activity measurements using a solution of 192Ir. All participants used the 4πβ–γ coincidence method, but four other methods were also applied, specifically 4πγ counting (3 laboratories), 4πCsI(Tl)βγ counting, 4πβ–4πγ sum counting and 4πβγ liquid scintillation counting. The unweighted mean value of the activity concentration was 1093.5 Bq mg−1 its standard uncertainty (1s), being 1.9 Bq mg−1. The total spread in the results is 2.5%. The weighted mean value and the median of the activity concentration were also evaluated. Results obtained with the International Reference System are compared with those derived from this comparison. The large spread of the results obtained with the 4πβ–γ coincidence method, together with the small value of the uncertainty assigned to the measurements by the participating laboratories, indicate that the data is perturbated by effects not yet understood and that further work is required before beginning a large-scale comparison of 192Ir.