Fission Cross-Section Ratio Measurements of ²³⁹Pu and ²³³U to ²³⁵U from 0.24 to 24 keV

The fission cross-section ratios of ²³⁹Pu to ²³⁵U and ²³³U to ²³⁵U have been measured from 0.24 to 24 keV using parallel-plate, back-to-back fission detectors and a slowing down lead spectrometer as a neutron source. Relative fission rates obtained from the experiments were converted to true fission cross-section ratios by detector intercalibration in a thermal-neutron flux. In the case of the Pu/U ratio, these results extend the data to below several keV where measurements have not previously been made and the ²³³U/²³⁵U results verify previous measurements made in this energy region.