Investigation of the spectra of neutrons originating from U-238 fission induced by 5.0-and 13.2-MeV neutrons

The spectra of neutrons accompanying U-238 fission induced by 5.0- and 13.2 -MeV primary neutrons are measured by the time-of-flight method. This inves tigation of fission-neutron spectra supplements previous measurements perfo rmed at the different primary energies of 2.9, 14.7, 16.0, and 17.7 MeV. Th e shape of the neutron spectrum at 13.2 MeV is similar to the shape of the neutron spectra for the primary energy of 14.7 MeV and higher. A calculatio n of the spectra within a conventional approach reproduces the shape of the observed distributions only at primary energies in excess of 2 MeV. In rel ation to a theoretical description, the experimental distributions for low primary energies show an anomalously high yield of soft neutrons. (C) 2001 MAIK "Nauka/Interperiodica"..