Measurements of the Neutron-Induced Fission Cross Sections of ²³⁴U, ²³⁶U, and ²³⁸U Relative to ²³⁵U from 0.1 to 30 MeV

We have measured the fission cross-section ratios ²³⁴U:²³⁵U, ²³⁶U:²³⁵U, and ²³⁸U:²³⁵U as a function of neutron energy from 0.1 to 30 MeV using ionization fission chambers and the time-of-flight technique at the Lawrence Livermore Laboratory 100-MeV electron linear accelerator. Our experimental procedure required accurate measurements of the isotopic composition of fissionable material within fission chambers containing a mixture of the threshold isotope (i.e., ²³⁴U, ²³⁶U, or ²³⁸U) and ²³⁵U. The measured cross-section ratios, averaged over the neutron energy interval 1.75 to 4.00 MeV, are 1.216 ± 0.012, 0.7166 ± 0.0072, and 0.4422 ± 0.0031, respectively.