Cause of the charge radius isotope shift at the \emph{N}=126 shell gap

TL;DR

This paper investigates the cause of the observed 'kink' in charge radius isotope shifts at the N=126 shell closure, emphasizing the role of neutron orbital occupation and effective interaction parameters.

Contribution

It identifies key factors in Skyrme interactions that influence the occupation of the 1$i_{11/2}$ neutron orbital, explaining the kink in isotope shifts.

Findings

Occupation of 1$i_{11/2}$ is crucial for the kink.

Spin-orbit field and effective mass affect orbital occupation.

Symmetry energy has little impact on the kink reproduction.

Abstract

We discuss the mechanism causing the `kink' in the charge radius isotope shift at the N=126 shell closure. The occupation of the 1$i_{11/2}$ neutron orbital is the decisive factor for reproducing the experimentally observed kink. We investigate whether this orbital is occupied or not by different Skyrme effective interactions as neutrons are added above the shell closure. Our results demonstrate that several factors can cause an appreciable occupation of the 1$i_{11/2}$ neutron orbital, including the magnitude of the spin-orbit field, and the isoscalar effective mass of the Skyrme interaction. The symmetry energy of the effective interaction has little influence upon its ability to reproduce the kink.