An improvement of uncertainty in activity standardization with efficiency tracer technique

The activities of ten pure β emitters were measured with two tracer nuclei for each one by using efficiency tracing technique. The determination results of specific activity of 35S, 63Ni and 185W, using efficiency tracers 60Co and 134Cs, are presented. The uncertainties of the final results for the three β emitting nuclides were 0.5% at 99.7% confidence. The relationship between β spectra and efficiency for the five nuclides were calculated with Fermi theory. The effects of the β spectra shapes, end-point energies and chemical form of the tracers on the β emitter activity results have been re-investigated. The type B uncertainty introduced by the upper limit of the fitting region (corresponding to the β low detection efficiency), the polynomial fitting power (60Co as tracer), the lower limit of the fitting region (corresponding to self-absorption) and the γ gate setting (134Cs as tracer) were investigated.