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

R. Gwin, R. R. Spencer, R. W. Ingle

Nuclear Science and Engineering / Volume 87 / Number 4 / Pages 381-404

August 1984

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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.

 
 
 
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