The spectra of neutrons emitted in fission of 232Th, 235Uand 238U 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 gmax= 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.
Abstract. The number and spectra of neutrons, in particular the number and spectra of prompt neutrons from the fission of actinides, at the intermediate energies represent important physical quantities, which determine the possibility of applying of one or another design of ADS. The multiplicities and energy distributions of prompt neutrons in interactions of 232 Th, 235,238 U and 237 Np with 50 and 96 MeV protons were measured by our group. The data are compared with results of recent measurements of the average multiplicities and spectra of prompt neutrons at the fission of 235,238 U induced by neutrons of the same energies. The correlation of the measured characteristics with neutron-proton compositions of composite nuclei is discussed. The similarity of characteristics for fission induced by neutrons and protons is noted.
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