Shell structure in neutron-rich Ca and Ni nuclei under semi-realistic mean fields

TL;DR

This study uses spherical Hartree-Fock calculations with semi-realistic interactions to explore shell structures in neutron-rich Ca and Ni nuclei, highlighting the role of tensor forces and effective interactions in shell magicity and submagic states.

Contribution

It demonstrates how specific ingredients of effective interactions, especially tensor forces, influence shell structures in neutron-rich nuclei, providing new insights into magic and submagic numbers.

Findings

N=32 is magic/submagic in 52Ca but not in 60Ni.

N=40 is submagic in 68Ni but not in 60Ca.

Loose binding may lead to N=58 submagic in 86Ni.

Abstract

Shell structure in the neutron-rich Ca and Ni nuclei is investigated by the spherical Hartree-Fock calculations with the semi-realistic $NN$ interactions. Specific ingredients of the effective interaction, particularly the tensor force, often play a key role in the $Z$ dependence of the neutron shell structure. Such examples are found in N=32 and N=40; N=32 becomes magic or submagic in $^{52}$Ca while its magicity is broken in $^{60}$Ni, and N=40 is submagic (though not magic) in $^{68}$Ni but not in $^{60}$Ca. Comments are given on the doubly magic nature of $^{78}$Ni. We point out that the loose binding can lead to a submagic number N=58 in $^{86}$Ni, assisted by the weak pair coupling.