Systematics of Nuclear Dissipation Around A \(=\) 200 Region

Abstract

We have studied the effect of nuclear dissipation on the fusion-fission dynamics by performing statistical model analysis of the available neutron multiplicity (\(\nu _{pre}\)) data of the even-even isotopes of Pb (Z= 82) in the mass range \(192\le A \le 204\), where strong shell effects are expected. Here, a comparative study with the neutron shell closure of neutron number N = 126 has been also carried out. Our statistical model calculation includes finer corrections such as shell effects, collective enhancement in the level density parameter (CELD), and modification in fission decay widths due to the orientation of the compound nuclear spin. The reduced dissipation strength \(\beta \) is used as a tunable parameter in order to reproduce the experimental data, viz-a-viz to understand the behavior of nuclear dissipation. Particularly, the influence of various properties of the target-projectile combination such as the fissility parameter and N/Z of the compound system are investigated to extract a systematic trend of the nuclear dissipation strength. The nuclear dissipation increases with the increasing value of the N/Z, and decreases with the increasing value of fissility for the nuclei of proton magic number Z= 82 and the neutron magic number N = 126. Nuclear dissipation also shows a strong dependence on the excitation energy. The higher values of \(\beta \) in the energy range 50–60 MeV indicate a strong dissipation effect due to the dominating nature of the shell effect and a clear systematics of the nuclear dissipation has not been observed in this energy range. Here, we have also studied the role of different forms of the level density parameter on the nuclear dissipation and a higher value of dissipation strength \(\beta \) is obtained when all the effects like CELD and shell correction in the level density are included.