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

Abstract

The spectra of neutrons accompanying ²³⁸U fission induced by 5.0-and 13.2-MeV primary neutrons are measured by the time-of-flight method. This investigation of fission-neutron spectra supplements previous measurements performed at the different primary energies of 2.9, 14.7, 16.0, and 17.7 MeV. The 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 calculation of the spectra within a conventional approach reproduces the shape of the observed distributions only at primary energies in excess of 2 MeV. In relation to a theoretical description, the experimental distributions for low primary energies show an anomalously high yield of soft neutrons.