Main text The APMP/TCRI Dosimetry Working Group performed the APMP.RI(I)-K4 key comparison of absorbed dose to water for 60Co between 2009 and 2010. Fourteen standards laboratories took part in the comparison. Three commercial cavity ionization chambers were used as transfer instruments and circulated among the participants. Nearly all the measured calibration coefficients for each ionization chamber were within one standard uncertainty (as estimated by the laboratory) of the comparison mean for that chamber, indicating reasonable agreement amongst the participants. Three participants (ARPANSA, PTB and NMIJ) were used to link the results to the BIPM through the ongoing bilateral BIPM.RI(I)-K4 comparison. Through this link the degree of equivalence (the ratio to the BIPM Key Comparison Reference Value and its uncertainty) was calculated for each non-linking laboratory to show the calibration capabilities. For the 9 eligible participants, this degree of equivalent ratio fell within 3.3 parts in 103 of unity, well within the combined standard uncertainty in all cases. 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).

The results are reported for an APMP.R(I)-K1.1 comparison that extends the regional comparison of standards for air kerma APMP.R(I)-K1 to several laboratories unable to participate earlier. The comparison was conducted with the goal of supporting the relevant calibration and measurement capabilities (CMCs) planned for publication by the participant laboratories.