Re-Evaluation Of The Bipm Standard For Air Kerma In Cs-137 Gamma Radiation

Following the change to the BIPM standard for air kerma in Co-60 adopted in November 2007, a re-evaluation of the BIPM standard for air kerma in Cs-137 radiation has been made. The changes to the air-kerma rate determination arise from three 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. The combined effect of these changes is an increase in the BIPM determination of the air-kerma rate by the factor 1.0030 and a reduction in the relative standard uncertainty of this determination to 1.9 parts in 10(3). A full uncertainty budget is presented.