Key comparison BIPM.RI(I)-K6 of the standards for absorbed dose to water of the ARPANSA, Australia and the BIPM in accelerator photon beams

A comparison of the dosimetry for accelerator photon beams was carried out between the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) and the Bureau International des Poids et Mesures (BIPM) in September and October 2012. The comparison was based on the determination of absorbed dose to water for three radiation qualities at the ARPANSA. Following receipt of the provisional comparison results, the ARPANSA decided to verify the geometry of the jacket and calorimeter core. This resulted in a change in the conversion factors applied by the ARPANSA to convert from absorbed dose to graphite to absorbed dose to water which was implemented after the comparison. The results for the revised standard, reported as a ratio of the ARPANSA and the BIPM evaluations, are 0.9965 at 6 MV, 0.9924 at 10 MV and 0.9932 at 18 MV, with a combined standard uncertainty of 5.5 parts in 103, 6.0 parts in 103 and 5.9 parts in 103, respectively. This result is the fifth in the on-going BIPM.RI(I)-K6 series of comparisons, and the first to be based solely on graphite calorimetry. (authors)