Application of “wet” extrapolation method for activity standardisation of electron capture radionuclides

The activity of electron capture radionuclides is usually determined by 4π(proportional counter, PC)–γ coincidence counting. The corrections necessary for the final activity value calculation are obtained by an extrapolation method. Variation of the PC detection efficiency can be achieved through different methods, e.g. by changing the self-absorption of the source using absorbing foils or by adding carriers. Another possibility is a “wet” extrapolation method, which utilises an absorption change during the drying of a water droplet added onto the source surface. In this paper, slopes of extrapolation curves and resulting activity values obtained by different methods are compared for several radionuclides (54Mn, 139Ce, 88Y, 57Co). In some cases a digital coincidence system was used for the analysis of measured data. The “wet” extrapolation, due to its very simple procedure, seems to be convenient for routine measurement and its accuracy is similar to the other methods.