Measurements of the average number of prompt neutrons emitted per fission of /sup 239/Pu and /sup 235/U. [0. 005 eV to 10 MeV]

Measurements of the average number of prompt neutrons ..nu.. bar/sub p/(E) emitted in neutron-induced fission of /sup 235/U and /sup 239/Pu relative to ..nu.. bar/sub p/ for spontaneous fission of /sup 252/Cf were made over an incident neutron energy range from 0.005 eV to 10 MeV. The incident neutrons were generated in pulses at the Oak Ridge Electron Linear Accelerator, and their energies, defined by time-of-flight methods. The samples were contained in fission chambers located in a large liquid scintillator. Fissions in the samples were identified by the simultaneous detection of prompt fission gamma rays in the scintillator and a pulse from the fission chamber. Fission neutrons were identified by the detection of the prompt gamma-ray cascade resulting from neutron absorption in gadolinium loaded in the liquid scintillator. The value of ..nu.. bar/sub p/(E) for /sup 239/Pu at 0.0253 eV agrees with the value given in EDNF/B-IV, whereas the corresponding value for /sup 235/U is about 0.7% larger than that given in ENDF/B-IV. 4 figures, 4 tables.