Update of the BIPM comparison BIPM.RI(II)-K1.I-131 of activity measurements of the radionuclide 131I to include the 2015 results of the BEV (Austria) and the POLATOM (Poland), the 2017 result of the NMISA (South Africa), and to link the CCRI(II)-S6.I-131 comparison

Three new participations in the BIPM.RI(II)-K1.I-131 comparison have been added to the previous results and this has produced a revised value for the key comparison reference value (KCRV), calculated using the power-moderated weighted mean. A link has been made to the CCRI(II)-S6.I-131 comparison piloted by the International Atomic Energy Agency (IAEA) in 2006, based on the participation of CMI-IIR in both comparisons. One NMI used the S6 comparison to update its degree of equivalence. The results of two NMIs in the CCRI(II)-S6.I-131 comparison were superseded by a more recent APMP.RI(II)-K2.I-131 comparison. The degrees of equivalence between each equivalent activity measured in the International Reference System (SIR) and the KCRV have been calculated and the results are given in the form of a table for the latest results in the BIPM.RI(II)-K1.I-131, and the linked CCRI(II)-S6.I-131, APMP.RI(II)-K2.I-131 and EURAMET.RI(II)-K2.I-131 comparisons. A graphical presentation is also given. © 2023 Institute of Physics Publishing. All rights reserved.