Possible bound nuclei beyond the two-neutron drip line in the $50\leqslant Z \leqslant 70$ region

TL;DR

This study predicts the existence of bound nuclei beyond the two-neutron drip line in the Z=50-70 region using a relativistic mean-field approach, revealing peninsulas of stability influenced by nuclear deformation and pairing effects.

Contribution

It introduces the prediction of new bound nuclei beyond the drip line in this region using the deformed relativistic Hartree-Bogoliubov theory, highlighting the role of deformation and pairing.

Findings

Bound nuclei beyond the drip line are predicted in Ba, Ce, Sm, Gd, Dy.

Deformation effects are crucial for the formation of stability peninsulas.

Decay rates of multi-neutron radioactivity are estimated for Ba and Sm isotopes.

Abstract

Possible bound nuclei beyond the two-neutron drip line in the $50\leqslant Z \leqslant 70$ region are investigated by using the deformed relativistic Hartree-Bogoliubov theory in continuum with density functional PC-PK1. Bound nuclei beyond the drip lines of $_{56}$Ba, $_{58}$Ce, $_{62}$Sm, $_{64}$Gd and $_{66}$Dy are predicted, forming peninsulas of stability in nuclear landscape. Near these peninsulas, several multi-neutron emitters are predicted. The underlying mechanism of the peninsulas of stability is investigated by studying the total energy, Fermi surface, quadrupole deformation and the single-neutron spectrum in the canonical basis. It is found that the deformation effect is crucial for forming the peninsulas of stability, and pairing correlations are also essential in specific cases. The dependence on the deformation evolution is also discussed. The decay rates of multi-neutron radioactivity in Ba and Sm isotopic chains are estimated by using the direct decay model.