Establishing measurement traceability for national laboratories: Results of an IAEA comparison of 131I

A radioactivity measurement comparison for solutions of 131I was conducted by the International Atomic Energy Agency for participants in one of its Cooperative Research Projects aimed at enhancing quality assurance practices in nuclear medicine. The comparison solutions were prepared from a single master stock solution and distributed to the participating laboratories, who measured the activity concentration of the solution using either the laboratory's radionuclide activity calibrator or primary standardization methods. From the 7 results received, a Comparison Reference Value was calculated to be 37.35(78) MBq g−1 at the reference time. Degrees of equivalence, as defined by the Mutual Recognition Agreement (MRA) of the Comité International des Poids et Mesures (CIPM), were calculated for each laboratory, demonstrating that equivalence to within ±4% could be achieved. The comparison has been registered as a supplementary comparison with the CIPM, Consultative Committee for Ionizing Radiation, Section II-measurement of radionuclides (CCRI(II)) for the purposes of allowing the participants to establish traceability to international standards for this radionuclide.