Abstract
The γ-ray self-absorption factor-the ratio of γ-ray intensities between cases with and devoid of self-absorption-was determined on 192Ir radiographic sources. The two methods were devised and used for evaluating the factor: (1) a target made up of layers of thin iridium discs was neutron activated to determine the ratio of γ-ray doses between that from the laminated source and the sum of the doses from the individual discs; (2) the quantity of radioactivity of 192Ir sources was estimated by approximate theoretical calculation, and the ratio was derived from the calculated quantity and the γ-ray dose observed.
Iridium targets were irradiated in the experimental hole of JRR-2, and after decaying off the 194Ir, the γ-ray dose from the sources were observed with an ionization chamber system. The factor obtained was 0.72 for 2mm diam. ×2mm thick source by the first method, and 0.89, 0.82, 0.70 and 0.66 for 0.5×0.5, 1×1, 2×2 and 4mm diam. × 4mm thick sources respectively, by the second method. The results agreed approximately with those theoretically obtained for sources of homogeneous distribution of the radioactivity, when based on the experimentally obtained value of 3.4cm-1 for the self-absorption coefficient.
