The charge polarization and its impact on prompt fission neutron multiplicity

Abstract

Prompt neutrons emitted from fission fragments of actinides show a specific induced-energy dependence. The mass distribution of prompt neutrons emitted from light fragments are independent of induced energies, while the number of prompt neutrons originating from heavy fragments increases with increasing induced energy. The understanding of the mechanism of this behavior has been a long standing problem, and cannot be solved unless we assume very artificial conditions such as fragment-mass dependent temperatures. Therefore, the neutron multiplicity has been used as fitted information in major models for prompt neutron spectra. In this paper, we evaluate the prompt neutron multiplicity as a function of the fission-fragment product of the n-induced fission of U-235 based on the fission configuration derived from the Langevin equation. We found that the charge polarization, which is the deviation from the unchanged charge distribution (UCD) assumption, can directly produce the specific induced-energy dependence of prompt neutrons without extra assumptions.