Possible Bound Nuclei Beyond The Two-Neutron Drip Line In The 50 <= Z <= 70 Region

Possible bound nuclei beyond the two-neutron drip line in the 50 <= Z <= 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 Ba-56, Ce-58, Sm-62, Gd-64, and Dy-66 are predicted, forming peninsulas of stability in the nuclear landscape. Near these peninsulas, several multineutron 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 multineutron radioactivity in Ba and Sm isotopic chains are estimated by using the direct decay model.