The absolute standardization of 32P and 204Tl at LNMRI

32P and 204Tl solutions were standardized within the frame of the international key comparisons organized by bureau international des poids et mesures, in 2002. The activity concentration of 32P was measured by counting solid sources in a 4πβ proportional gas flow counter and by liquid scintillation counting. The self-absorption in solid sources for 4πβ counting and the presence of 33P as an impurity were evaluated. The combined standard uncertainty for 32P was 0.59% in the 4πβ counting and 0.38% in the liquid scintillation counting. Liquid scintillation counting was used to measure the activity concentration of 204Tl with combined standard uncertainty of 0.35%.