CIPM MRA COMPARISON REPORTS

A new direct key comparison of the standards for air kerma of the Physikalisch-Technische Bundesanstalt (PTB), Germany, and the Bureau International des Poids et Mesures (BIPM) was carried out in the ⁶⁰Co radiation beam of the BIPM in February 2024. The comparison result, evaluated as a ratio of the PTB and the BIPM standards for air kerma, is 1.0004 with a combined standard uncertainty of 2.5 parts in 10³. The results for an indirect comparison made at the same time are consistent with the direct comparison result at the level of 3.4 parts in 10³. The result of the direct comparison agrees with the direct comparison carried out in 2014 at the level of the combined standard uncertainty, when updated with the changes implemented to the standards at each laboratory. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database.