Comparisons for the national standards of air kerma from therapy level and radiation protection gamma-ray beams were conducted by the NIST and the Bureau International des Poids et Mesures (BIPM).
Transfer ionization chambers were calibrated in terms of air kerma in the radiation beams of both institutes. For the therapy level comparison, carried out in a 60Co gamma-ray beam, two transfer chambers were used with volumes of 1 cm3 and 3 cm3. The comparison result, K R , taken as the mean of the results for both chambers, was K R = 1.0039 with a combined standard uncertainty for the comparison of 0.0034. The radiation protection level comparison was conducted in both 137Cs and 60Co gamma-ray beams. For this part of the comparison, two transfer chambers of the same model and volume of 100 cm3 were used. The comparison result for 60Co was K R = 1.0023 and for 137Cs was K R = 0.9990. The results from the therapy level comparison are available on the BIPM website.