Comparison of the standards for air kerma of the NPL and the BIPM for⁶⁰Co γ rays

An indirect comparison of the standards for air kerma of the National International des Poids et Mesures (BIPM) was made in Co-60 gamma radiation in September 2007. The comparison result, based on the calibration coefficients for two transfer chambers and expressed as a ratio of the NPL and the BIPM standards for air kerma, is 1.0011 (0.0038). The degrees of equivalence between the NPL and the other participants in the key comparison have been calculated and the results are presented in the form of a matrix. A graphical presentation is also given.