Measurement of the Fission Cross Sections of Uranium-233 and Plutonium-239 Relative to Uranium-235 from 1 keV to 30 MeV

The fission cross-section ratios of ²³³U to ²³⁵U and ²³⁹Pu to ²³⁵U were measured over the neutron energy range from 1 keV to 30 MeV at the Lawrence Livermore Laboratory 100-MeV Linac. Ionization fission chambers and the time-of-flight technique were used to take data simultaneously over the entire energy range. This provided accurate determinations of the shape versus neutron energy of the ratios. Two independent methods were used to determine the average value of each ratio in the interval from 1.75 to 4.0 MeV for the purpose of normalization. Over the 1-keV to 30-MeV range, the total uncertainties for the ²³³U-to-²³⁵U data range from 2 to 4%; the ²³⁹Pu-to-²³⁵U data uncertainties range from 1 to 4%.