Shell evolution and its indication on the isospin dependence of the spin-orbit splitting

TL;DR

This paper investigates how shell evolution in neutron-rich nuclei affects the spin-orbit potential and the emergence or erosion of traditional and new magic numbers, revealing the complex interplay between nuclear potential depth and shell closures.

Contribution

It demonstrates how modifications to the spin-orbit potential influence shell closures, leading to the disappearance of some traditional magic numbers and the emergence of new ones in neutron-rich nuclei.

Findings

Traditional magic numbers like N=8, 20 are eroded in neutron-rich nuclei.

New magic numbers such as N=6, 14, 16, 32, 34 emerge due to spin-orbit effects.

The N=82 shell closure remains robust in neutron-rich environments.

Abstract

The available experimental data on shell evolution indicate that the strength of the spin-orbit (SO) single-particle potential may be enhanced in neutron-rich nuclei. We observe that such a simple scheme destroys the Harmonic Oscillator (HO) magic numbers N=8 and 20 and generates new SO magic numbers like N=6, 14, 16, 32 and 34. The traditional SO magic numbers like N=28 and 50 and N=14 seen in $^{22}$O are eroded somehow in neutron-rich nuclei due to the sensitivity of larger-$l$ orbitals to the depth of the central potential but they are more robust than the HO magic numbers. The N=82 shell closure persists in neutron-rich nuclei while HO shell closures like N=40 and 70 do not emerge. Both mechanisms contribute to enhancing the N=56 and 90 gaps by splitting the $1d_{5/2}$ and $0g_{7/2}$ and the $0h_{9/2}$ and $1f_{7/2}$ orbitals.