Measurement of the Ratio of Fission Product Gamma Activities from 239Pu and 235U Fissions

The ratio of the γactivities per fission from fission products of 239Pu and 235U, and its time dependence were measured by double fission chamber technique. The γ-activity from the fission products of 239Pu fission was lower than the corresponding activity relevant to 235U fissions. The ratio varied with the cooling time allowed after irradition. This ratio was applied to power distribution measurements by γ-scanning method in multi-region cores composed of PuO2-UO2 and UO2 fuels. To obtain the relative power, the measured γ-activities from the fission products in the fuel rods were corrected for the difference between the γ-activities per fission from the fission products.