Parameterization of prompt neutron multiplicity for first-chance actinide photofission

Abstract

A parametric description of the dependence of the average number of prompt neutrons on the mass of fragments ν(A) from the actinides ( 235 U and 238 U) photofission has been developed for the range of energies of the first chance of fission (from thresholds of (γ,f) reaction to thresholds of (γ,nf) reactions). The proposed method gives a possibility to describe the dependence of "saw-tooth" behavior of prompt neutron yield from fission fragments, using several free parameters dependent on the energy and composition of nucleons, and to predict ν(A) for other isotopes of actinides. The phenomenological Wahl method was applied to estimate the number of neutrons emitted by corresponding fission fragments of atomic mass A. The total averaged number of prompt neutrons needs to construct the parametrizing function, which reasonably reproduces the characteristic features of its behavior and parameterization of an average number of prompt neutrons. To verify the proposed parametrization, according to the established fact of the equivalence of the formation of identical compound nuclei caused by reactions stimulated by photons and neutrons, calculations were carried out for the compound nuclei 234 U*, 236 U*, 238 Np*, 240 Pu*, formed as a result of neutron fission reactions for which the experimental data is