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Volume :38 Issue : 1 2011      Add To Cart                                                                    Download

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

Auther : M.M. SHARMA AND A.A. SALDANHA

Physics Department, Faculty & Science, Kuwait University, P.O.Box 5963, Safat 13060, Kuwait

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 ù-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 â-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.

Keywords: Relativistic mean-field theory; NL-SV1, rare-earth nuclei; binding energies; quadrupole deformation; two-neutron separation energies, shape-coexistence; shell effects; r-process nucleosynthesis; neutron drip line; single-particle levels; stability beyond drip line.

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