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

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 w-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 /3-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 an enhanced stability beyond the drip line.