Neutron-Induced Fission Cross-Section Ratios for ²³⁹Pu, ²⁴⁰Pu, ²⁴²Pu, and ²⁴⁴Pu Relative to ²³⁵U from 0.5 to 400 MeV

The fission cross-section ratios for isotopic targets of ²⁴⁰Pu, ²⁴²Pu, and ²⁴⁴Pu relative to ²³⁵U are measured for neutron energies from 0.5 to 400 MeV and for ²³⁹Pu relative to ²³⁵U for energies from 0.85 to 62 MeV. A multiple-plate gas ionization detector was used to measure simultaneously the fission rate for each of the isotopic targets. The neutron energies were determined by the time-of-flight technique on a 20-m flight path at the Weapons Neutron Research white neutron source at the Los Alamos National Laboratory Neutron Science Center. Uncertainties are <4% for energies <50 MeV. This measurement provides the capability to resolve discrepancies among previous measurements for these isotopes over this energy range and are the first measurements for most of these isotopes for energies >30 MeV. The results are compared with previous measurements and to ENDF/B-VI.