Determination of shell correction energies at saddle point using pre-scission neutron multiplicities

No influence of aN=126neutron-shell closure in fission-fragment mass distributions

“…It is found, in general, while the ground state mass is strongly influenced by the shell correction, the saddle point mass should be rather close to its macroscopic value [6,10]. In contrast, a few recent experimental studies indicated rather strong effect of shell correction at the saddle point, particularly around N=126 shell closed nuclei [2,4,11]. An anomalous increase in fission fragment angular anisotropy was observed in the fission of 210 Po at excitation energy ∼40-60 MeV, which was conjectured as an indirect evidence of shell correction at saddle due to neutron shell closure at N=126 [2,11].…”

“…The role of nuclear shell effects on various nuclear reaction processes as a function of excitation energy, specially for the nuclei around the shell closure, has currently remained an issue of intense discussions [1][2][3][4][5][6][7][8][9]. Apart from the basic understanding point of view, a large part of the recent activities were concentrated on the study of shell effect in fission of heavy nuclei with the aim to unveil the relationship between nuclear structure and nuclear stability.…”

Into the Fission Valley of 'magic Nucleus' Polonium

“…The pre-scission neutron multiplicity, measured in an experiment at the Inter University Accelerator Centre (IUAC), New Delhi, for 206,210 Po. The result also indicated [12] the requirement of substantial shell correction not only in shell closed 210 Po but also in 206 Po. The analysis of both the angular anisotropy and pre-scission neutron data mentioned above, were carried out within the framework of the wellestablished statistical models.…”

“…A few recent experimental and theoretical studies [11,12,13,14], however, indicated dramatic ambiguity regarding the presence or absence of shell effects (correction) at the saddle point. Saddle point is the point of no return, so that a nucleus, if deformed beyond this point, will have no choice but to undergo fission, leading to two heavy fragments of nearly equal mass.…”

“…Therefore mass distributions of the nuclei 210,206 Po were studied [9] by the researchers at Variable Energy Cyclotron Centre. The nuclei were populated by bombarding 12 [9] provides benchmark data to test the new fission dynamical models to study the effect of shell correction on the potential energy surface at fission saddle point. Figure 2: Variation of the standard deviation of the fitted symmetric mass distribution with excitation energy.…”