Shape Coexistence in Ni 78 as the Portal to the Fifth Island of Inversion
Résumé
Large-scale shell-model calculations predict that the region of deformation which comprises the heaviest
chromium and iron isotopes at and beyond N ¼ 40 will merge with a new one at N ¼ 50 in an astonishing
parallel to the N ¼ 20 and N ¼ 28 case in the neon and magnesium isotopes. We propose a valence space
including the full pf shell for the protons and the full sdg shell for the neutrons, which represents a
comeback of the the harmonic oscillator shells in the very neutron- rich regime. The onset of deformation is
understood in the framework of the algebraic SU(3)-like structures linked to quadrupole dominance. Our
calculations preserve the doubly magic nature of the ground state of 78Ni, which, however, exhibits a welldeformed
prolate band at low excitation energy, providing a striking example of shape coexistence far from
stability. This new IOI adds to the four well-documented ones at N ¼ 8, 20, 28, and 40