Neutron Emission from Prompt Fragments in the Fission of Excited Nuclei

Abstract

Our improved approach combining the renormalized Fermi-gas model (RGM) with the use of an average collective potential energy surface (PES) has been used to estimate the energy release in prompt fission phenomena from fission of excited nuclei. The role of excess excitation $\ensuremath{\Delta}{U}_{I}$ on top of the fission barrier, under several assumed constraints, is discussed. The partition of $\ensuremath{\Delta}{U}_{I}$ into the conjugate prompt fragments has been calculated from a simple RGM saturation condition. The practical limits of $\ensuremath{\Delta}{U}_{I}$ have been discussed from the viewpoint of the statistical model of nuclear reactions. The number of evaporated neutrons from the prompt fragments ${\ensuremath{\nu}}_{F}$ has been estimated from LeCouteur and Lang's approximation using Wing and Varley's neutron binding-energy tables. Fairly satisfactory agreement for the number ${\ensuremath{\nu}}_{F}$ has been obtained with the experimental work on fission of $^{230}\mathrm{Th}$ by 25.7- and 29.5- MeV $^{4}\mathrm{He}$ ions and of $^{226}\mathrm{Ra}$ by 13.0-MeV protons. A linear relationship of the average number of prompt neutrons $\overline{\ensuremath{\nu}}$ with $\ensuremath{\Delta}{U}_{I}$ is predicted from our model.