Standardization of the radionuclides Co-60 and Fe-59 by digital 4 pi beta(PC)-gamma (NaI) coincidence counting

摘要

The digital coincidence counting (DCC) technique has been developed at NIM, China to replace the classical analog coincidence units in the 4 pi beta-gamma counting system. The detector system comprises two NaI (Ti) gamma-ray detectors and a 4 pi beta 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 Co-60 in the KCDB and contribute to the APMP.RI(II)-K2.Fe-59 comparison, Co-60 and Fe-59 dry sources were prepared and measured using the digital 4 pi beta(PC)-gamma(NaI) coincidence system by applying the efficiency extrapolation method. For Co-60 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 Fe-59, 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 gamma spectrometry, which was calibrated by using a series of standard point sources from PTB. (C) 2015 Elsevier Ltd. All rights reserved.