The results of a regional supplementary comparison of air kerma standards from eight standards laboratories are presented. The three transfer ionisation chambers (two model Exradin A4 chambers and one Exradin A5 chamber manufactured by Standard Imaging, Inc, Middleton, MI, USA) were measured at each laboratory over the period 2013 to 2016. Air kerma calibration coefficients for the transfer instruments were compared for the ISO 4037 narrow- and wide-spectrum series of x-ray beams, in the range from 30 kV to 300 kV. Results from the five primary standard and three secondary standard laboratories were obtained. For each radiation quality, the results were expressed as the ratio of the laboratory to the comparison reference value, which was the average of three laboratories selected for this purpose before the comparison began. The A5 transfer standard was also compared for air kerma at protection-level 137Cs gamma rays. Laboratories reported their conversion coefficients for ambient dose equivalent, H*(10), and so the comparison also served as an indirect test of this quantity. Overall, the laboratories were in general agreement within the expanded uncertainties claimed by the laboratories. The comparison is designated APMP.RI(I)-S3 under the international arrangements for comparisons conducted to support the CIPM MRA. 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 the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

A comparison has been made of the air-kerma standards for low-energy x rays at the National Institute of Standards and Technology (NIST) and the Physikalisch-Technische Bundesanstalt (PTB). The comparison involved a series of measurements at the PTB and the NIST using the air-kerma standards and two NIST reference-class transfer ionization chamber standards. Results are presented for the reference radiation beam qualities in the range from 25 kV to 50 kV for low energy x rays, including the techniques used for mammography dose traceability. The tungsten generated reference radiation qualities, between 25 kV and 50 kV used for this comparison, are new to NIST; therefore this comparison will serve as the preliminary comparison for NIST and a verification of the primary standard correction factors. The mammography comparison will repeat two previously unpublished comparisons between PTB and NIST. The results show the standards to be in reasonable agreement within the standard uncertainty of the comparison of about 0.4 %.