Standardization of 169Yb by the 4πβ-γ method

169Yb was standardized in the framework of an EUROMET international comparison. Two solutions, with approximately activity concentrations of 16 MBq g−1 and 1.6 MBq g−1 were distributed to the participants by BNM-LPRI-(France). In the Radionuclide Metrology Laboratory of INFIN-HH, the weak solution was standardized using a coincidence method, applying the ‘beta-efficiency extrapolation’ variant. A simple 4π beta-gamma coincidence equipment was used. Due to the presence of a metastable state with a half-life of 0.66 μs in the decay scheme of 169Tm, a resolution time of 5.1 μs was chosen for the coincidence module. A gamma threshold of 150 keV was used. A second degree extrapolation graph was used, providing an activity concentration value of 1.18 MBq g−1 at 15 November 1997, 12 h UT. The combined uncertainty was 0.9%. Using the dilution factor provided by BNM-LPRI, the corresponding activity concentration for the strong solution is 11.989 MBq g−1 (uA=0.110MBqg−1; 0.92%).