Abstract. A re-evaluation of the BIPM standard for air kerma in ⁶⁰Co radiation has been made. The changes to the air-kerma rate determination arise from four sources: (i) the results of Monte Carlo calculations of correction factors for the standard; (ii) a re-evaluation of the correction factor for saturation; (iii) a new evaluation of the air volume of the standard using an experimental chamber of variable volume; (iv) the adoption of a new reference beam at the BIPM. The combined effect of these changes is an increase in the BIPM determination of air-kerma rate by the factor 1.0054 and a reduction of the relative standard uncertainty of this determination to 1.5 parts in 10³. A full uncertainty budget is presented. The new standard is effective from 1 November 2007.

Print publication: Issue 6 (December 2007)
Received 10 September 2007
Published 11 October 2007