Re-evaluation of the BIPM international dosimetry standards on adoption of the recommendations of ICRU Report 90

Following the recommendations of ICRU Report 90, a re-evaluation has been made of the BIPM standards for air kerma in x-rays and in 60Co and 137Cs γ-radiations, for absorbed dose to water in 60Co γ-radiation and for reference air-kerma rate in 192Ir γ-radiation for brachytherapy. The changes arise from three sources: (i) the implementation of new correction factors kii and kW for free-air ionization chambers; (ii) a re-evaluation of the mean excitation energy for graphite and water and the density effect for graphite; (iii) new stated uncertainties for the value of Wair for dry air and for the related product Wairsg,air. Consideration has also been given to new recommendations for photon interaction coefficients, although no corresponding changes have resulted. The heat defect in graphite is also considered. A summary table of the combined effect of these changes is presented. The new standards will be implemented on 1 January 2019.

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