Standardization of the radionuclides 60Co and 59Fe by digital 4πβ(PC)-γ(NaI) coincidence counting

The digital coincidence counting (DCC) technique has been developed at NIM, China to replace the classical analog coincidence units in the 4πβ-γ counting system. The detector system comprises two NaI (Tl) γ-ray detectors and a 4πβ proportional counter (PC) operated with a mixture of argon and methane at atmospheric pressure in a gas flow arrangement. To update the activity results of radionuclide 60Co in the KCDB and contribute to the APMP.RI(II)-K2.Fe-59 comparison, 60Co and 59Fe dry sources were prepared and measured using the digital 4πβ(PC)-γ(NaI) coincidence system by applying the efficiency extrapolation method. For 60Co nuclide, the activity concentration value equal to 290.6 kBq g−1 with a relative standard uncertainty of 0.26%, is consistent with the result given by the calibrated ionization chamber. For the nuclide 59Fe, the activity concentration value at the reference date was 471.7 kBq g−1 with a relative standard uncertainty of 0.34%. This value is in good agreement with the result obtained with the HPGe γ spectrometry, which was calibrated by using a series of standard point sources from PTB.