ELECTRON-CAPTURE EFFECTS IN ACTIVITY DETERMINATION OF IR-192 BY A 4-PI BETA-GAMMA COINCIDENCE COUNTING METHOD

The radioactivity of Ir-192 was measured by using a 4 pi beta-gamma co incidence counting system with a pressurized 4 pi proportional counter and two NaI(TI) scintillation detectors. An efficiency-extrapolation method using low-energy threshold-level variation was applied to deter mine the activity of Ir-192. In order to investigate the influences of the electron-capture decay of Ir-192 on the activity measurement, the measurement was carried out using four different gamma gates. The inf luences of the decay process were evaluated from the decay-scheme para meters and the count rates obtained from these gates and then used to make the necessary corrections in order to determine the activity. The final results obtained from each gamma gate showed good agreement wit hin one standard deviation.