Standardization of 65Zn

Two absolute methods were used for standardizing the 65Zn solution received within the framework of the 2002–2003 full-scale BIPM comparison. The first method was the 4πPC-γ-coincidence with efficiency extrapolation. The measurement conditions were adjusted so that the slope of the extrapolation curve was absent, which ensured that the measurement result did not depend on the positron branch intensity. When using the second method, the KX-γ-coincidence counting with two NaI(Tl) scintillation crystals of different thicknesses, extrapolation was not needed, but a correction for the positron branch was necessary. It is shown that the 4πPC-γ-coincidence method has a significantly larger uncertainty, and it is necessary to pay attention to the uncertainty component connected with setting the γ-channel mode, which is characteristic for 65Zn only.