Correlation effect in activity measurement of 59Fe

Activity determination of (59)Fe by 4π beta-gamma counting using liquid scintillation in the beta channel

This paper reports on absolute activity measurements of iron-59 made at the National Metrology Institute of South Africa (NMISA) via 4π(LS)β-γ coincidence counting. The exercise formed part of an Asia Pacific Metrology Program (APMP) regional key comparison. Source data were analysed by the extrapolation technique for a number of gamma-ray window settings. In addition, a feasibility study was undertaken on a second technique; a non-extrapolation method based on a detection efficiency analysis. The reported activity concentration of the (59)Fe solution was determined with a relative uncertainty of 0.28% (k=1), the uncertainty being due mainly to the rate vs. efficiency fitting process. The result from the non-extrapolation method was lower than that given by extrapolation by 0.33%, within two standard deviations. Possible reasons for the small discrepancy are discussed.

Standardization of 152Eu and 88Y

The activities of 152Eu and 88Y have been measured by the digital coincidence counting (DCC) technique and compared with those of the conventional coincidence counting technique. In the DCC, the pulse amplitudes from both beta and gamma channels are digitized in commercial ADCs and the pulse input times are simultaneously determined by 10 MHz oscillation clock installed in the coincidence module. The activity of the measured source is determined from the information of pulse height and input time for each pulse by off-line analysis. The activity of 152Eu was determined from extrapolations of efficiency functions obtained at 3gamma gates and the result showed a good agreement with that of the conventional method with 0.2% of uncertainty. The activity of 88Y was also determined by the DCC technique, and the reliability of the result was proved through Asia Pacific Metrology Program (APMP) inter-comparison of 88Y.