Update of the BIPM comparison BIPM.RI(II)-K1.Ba-133 of activity measurements of the radionuclide 133Ba to include the 2016 result of the NRC (Canada), the 2018 result of the TENMAK-NÜKEN (Türkiye), the 2019 result of the NMISA (South Africa) and the 2019 result of the NIST (United States)

Main text Since 1977, 23 laboratories have submitted 45 samples of 133 Ba to the International Reference System (SIR) for activity comparison at the Bureau International des Poids et Mesures (BIPM), with comparison identifier BIPM.RI(II)-K1.Ba-133. Recently, the NRC (Canada), the TENMAK-NÜKEN (Türkiye), the NMISA (South Africa) and the NIST (United States) participated in the comparison and the key comparison reference value (KCRV) has been updated. The degrees of equivalence between the updated KCRV and each equivalent activity measured in the SIR or linked to the SIR from the APMP.RI(II)-K2.Ba-133 comparison have been calculated and the results are given in the form of a table. A graphical representation is also given. 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 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).