ANALYTICAL CALCULATIONS ON RADIOACTIVITY MEASUREMENTS OF IR-192 METALLIC SOURCES WITH A CALIBRATED IONIZATION-CHAMBER

The self-attenuation of photons was analytically calculated for an Ir- 192 metallic wire source and an aqueous standard source. The influence of the self-attenuation on the current of the calibrated ionization c hamber was also evaluated. The self-attenuation did considerably affec t the ionization current. It was concluded that the apparent radioacti vity must be multiplied by a correction factor larger than unity (1.09 +/-0.01 in the present case) to get the true radioactivity when the ra dioactivity of the Ir-192 metallic wire source was measured with the i onization chamber calibrated with the aqueous standard source of Ir-19 2.