Measurements of the Energy Dependence of Prompt Neutron Emission from ²³³U, ²³⁵U, ²³⁹Pu, and ²⁴¹Pu for E_n = 0.005 to 10 eV Relative to Emission from Spontaneous Fission of ²⁵²Cf

A series of experiments has been performed to measure the dependence on the incident neutron energy of the average number of prompt neutrons emitted per fission from ²³³U, ²³⁵U, ²³⁹Pu, and ²⁴¹Pu relative to the average number of prompt neutrons emitted in spontaneous fission of ²⁵²Cf The incident neutron energy range was 0.005 to 10 eV. A white neutron source was generated by the Oak Ridge Electron Linear Accelerator and the energies of the neutrons incident on the fissile samples were determined by time-of-flight techniques. In each experiment, the samples, including the ²⁵²Cf standard, were contained in different sections of a fission chamber that was surrounded by a large volume (0.91 m³) of liquid scintillator loaded with gadolinium. The fission chamber detected fission events, and the scintillator detected the accompanying prompt neutrons. The resulting data were analyzed to yield: = (E) (fissile)/(²⁵²Cf). Only for ²³⁹Pu was any neutron energy dependence definitely confirmed, with for ²³⁹Pu being lower by 0.7% in the resonance at 0.3 eV than it was near 0.025 eV. For incident energies of 0.02 to 0.05 eV, values of were 0.6597 ± 0.0018 for ²³³U, 0.6443 ± 0.0014 for ²³⁵U, 0.7655 ± 0.0014 for ²³⁹Pu, and 0.7820 ± 0.0018 for ²⁴¹Pu.