Stability beyond the neutron drip-line near the third peak of the r-process nucleosynthesis

TL;DR

This study uses relativistic mean-field theory to explore nuclear stability near the third r-process peak, revealing that certain nuclei exhibit unexpected stability beyond the neutron drip line due to deformation effects.

Contribution

It demonstrates that nuclear deformation can lead to stability beyond the neutron drip line near the third r-process peak, a novel insight into nuclear structure.

Findings

Nuclear shell effects at N=126 remain strong far from stability.

Some nuclei near N~132-134 show enhanced neutron separation energy.

Deformation causes single-particle energy levels to shift, enabling stability beyond the drip line.

Abstract

We have investigated the nuclear shell effects at N=126 in the region of the third peak of the r-process nucleosynthesis within the framework of the relativistic mean-field theory using the Lagrangian model NL-SV1 with the vector self-coupling of omega-meson. Our study encompasses even-even nuclei with N=110-140 in the isotopic chains of Hf (Z=72) down to Ba (Z=56). It is shown that the nuclear shell effects at N=126 remain strong even as one moves far away from the line of the beta-stability. As the neutron drip line approaches N=126, nuclei exhibit vanishingly small neutron separation energy. However, going beyond the neutron drip line, we observe an interesting feature in that some nuclei near N ~ 132-134 for the isotopic chains of Z=62-68 show enhanced neutron separation energy. This is especially pronounced for the isotopes of Gd (Z=64) and Dy (Z=66). These nuclei exhibit the phenomenon of stability beyond the neutron drip line. Our analysis of the single-particle spectrum shows that this is engendered by the deformation assumed by these nuclei with the consequence that the neutron single-particle spectrum is pushed down in energy, thus leading to enhanced stability beyond the drip line.