Since 1976, ten national metrology institutes (NMIs) and another laboratory have submitted 21 samples of known activity of ¹³⁹Ce to the International Reference System (SIR) for activity comparison in the BIPM.RI(II)-K1.Ce-139 comparison at the Bureau International des Poids et Mesures. The activities ranged from about 0.5 MBq to 55 MBq. The key comparison reference value (KCRV) has been recalculated to include the new National Metrology Institute of Japan (NMIJ) result. The degrees of equivalence between each equivalent activity measured in the SIR and the new KCRV have been calculated and the results are given in the form of a matrix for nine NMIs and the BIPM. A graphical presentation is also given. The results of an APMP.RI(II)-K2.Ce-139 comparison held in 2004 have been linked to the SIR results through the submission to the SIR of an ampoule by the pilot laboratory, the NMIJ. This has enabled one NMI to update its 1999 SIR entry and one NMI to update their previously published 1976 CCRI(II) comparison results and three other NMIs to have degrees of equivalence for activity measurements for this radionuclide.

Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.

The final report has been peer-reviewed and approved for publication by Section II of the Consultative Committee for Ionizing Radiation (CCRI(II)), according to the provisions of the Mutual Recognition Arrangement (MRA).