New data on prefission neutrons

The spectra of neutrons emitted in fission of232Th,235U and238U induced by 2.9- and 14.7- MeV neutrons (below and above the chance fission threshold, respectively) were measured by the time-of-flight method. Two effects were observed in the prefission neutron spectra: the high-energy wing is related to the nonequilibrium mechanism of emission up to the well pronounced upper boundary of ɛmax=8.5 MeV; in the lower-energy wing e < 2 MeV, neutron yield exceeds conventional statistical model description. The latter effect was attributed to the fission process dynamics.