Search for an effect of shell closure on nuclear dissipation via a neutron-multiplicity measurement

Abstract

The prescission neutron multiplicity excitation function is measured for the first time for three isotopes across a major closed shell in order to investigate the shell effects on fission hindrance. Three isotopes of Fr (${}^{213,215,217}$Fr) are populated by fusion of ${}^{19}\mathrm{F}{+}^{194,196,198}$Pt in the excitation energy range of 46.6--91.8 MeV. While ${}^{213}$Fr has a major neutron shell closure at $N=126$, ${}^{215}$Fr and ${}^{217}$Fr are away from the closed shell. It is found from the statistical model analysis of the experimental data that the strengths of nuclear dissipation for nuclei away from shell closure are very similar. On the other hand, the dissipation is relatively weaker for a shell-closed nucleus in comparison to adjacent nuclei away from shell closure.