Neutron emission in fission

A model based on energy conservation with a detailed simulation of the cascade neutron emission process from exited fragments was applied for prompt neutron emission calculations. The results for the prompt neutron multiplicity, ν(A), the neutron energy, ε(A), as a function of fission fragment mass A and total kinetic energy (TKE), ν(TKE) are compared with available experimental data for the spontaneous fission of 252Cf, 244,248Cm and thermal neutron induced fission of 235U. Several problems connected with the distribution of the available energy between exited fragments and the mechanisms of neutron emission in fission are discussed. The high TKE range >190 MeV is assumed as a possible region for scission neutron emission. In the framework of this assumption, an excellent agreement between experimental and calculated data for the TKE range from 150 MeV to 205 MeV (containing ∼98% of all fission events) within 1-2% was found for all spontaneously fissioning isotopes mentioned above. An additional unfolding between the calculated results and the rather poor experimental energy resolution improved the agreement also in case of 235U(nth, at f). However, one may conclude that in spite of the good agreement between the results of three experimental investigations for 235U(nth, at f), they maybe all have similar systematic uncertainties which result in a common observation, namely a very low neutron multiplicity and a positive slope of dν/dE in the low TKE range (<150 MeV)