CIPM MRA COMPARISON REPORTS

A key comparison of the measurement of the activity per unit mass of a solution of ²²⁵Ac in equilibrium with its progeny, was organized in 2024. Flame sealed ampoules filled with master solution of ²²⁵Ac were prepared and distributed by NPL, based on the provision of ²²⁵Ra by the CERN-MEDICIS platform in the framework of the PRISMAP project. Seven laboratories participated, and all the submitted final values were obtained using primary measurements based on liquid scintillation (i.e., TDCR and CIEMAT/NIST methods). A dedicated ampoule was also submitted to the International Reference System (SIR) at BIPM for a future link to the BIPM.RI(II)-K1.Ac-225 comparison using the activity measurement provided by LNE-LNHB. This report describes the main aspects of the comparison, including the values submitted by the participants, used to calculate the Comparison Reference Value (CRV) and provisional degrees of equivalence for each laboratory. This study was supported by the project 22HLT03 AlphaMet, which has received funding from the European Partnership on Metrology (EPM), co-financed from the European Union's Horizon Europe Research and Innovation Programme and by the participating States.

Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.

The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).