High-Resolution Fission Cross-Section Measurements of ²³⁵U and ²³⁹Pu

The fission cross sections of ²³⁵U and ²³⁹Pu are measured with very high neutron energy resolution (0.17 ns/m) in the energy region from 100 to 2000 eV for ²³⁵U and to 20000 eV for ²³⁹Pu. The purpose of this measurement is to provide fission cross sections with energy resolution comparable with that available from transmission measurements for the purpose of deriving multilevel resolved resonance parameters. Fission ion chambers are used to detect fission fragments, and a ¹⁰B ionization chamber is used to measure the relative neutron flux at the 86-m flight path of the Oak Ridge Electron Linear Accelerator. The measured fission cross sections are the highest resolution measurements of good accuracy reported in the neutron energy range above 400 eV.