Fission barrier, damping of shell correction and neutron emission in the fission of A$\sim$200

TL;DR

This study analyzes the decay of $^{210}$Po in fusion reactions, determining a fission barrier of 21.9 MeV, and highlights the role of dynamical neutrons and fission delay in low-energy fission processes.

Contribution

It provides a consistent model incorporating shell correction damping and estimates the fission delay time, advancing understanding of neutron emission and fission dynamics in A~200 nuclei.

Findings

Fission barrier of 21.9 MeV accurately describes excitation functions.

Dynamical neutrons contribute significantly at low excitation energies.

Fission delay time estimated at approximately 0.8 x 10^{-19} seconds.

Abstract

Decay of $^{210}$Po compound nucleus formed in light and heavy-ion induced fusion reactions has been analyzed simultaneously using a consistent prescription for fission barrier and nuclear level density incorporating shell correction and its damping with excitation energy. Good description of all the excitation functions have been achieved with a fission barrier of 21.9 $\pm$ 0.2 MeV. For this barrier height, the predicted statistical pre-fission neutrons in heavy-ion fusion-fission are much smaller than the experimental values, implying the presence of dynamical neutrons due to dissipation even at these low excitation energies ($\sim$ 50~MeV) in the mass region A $\sim$ 200. When only heavy-ion induced fission excitation functions and the pre-fission neutron multiplicities are included in the fits, the deduced best fit fission barrier depends on the assumed fission delay time during which dynamical neutrons can be emitted. A fission delay of (0.8 $\pm$ 0.1 )$\times 10^{-19}$ s has been estimated corresponding to the above fission barrier height assuming that the entire excess neutrons over and above the statistical model predictions are due to the dynamics. The present observation has implication on the study of fission time scale/ nuclear viscosity using neutron emission as a probe.