Shell effects in nuclear charge radii based on Skyrme density functionals

TL;DR

This paper investigates how a new term related to neutron and proton pairing influences nuclear charge radii across the nuclide chart, improving theoretical models' accuracy in capturing shell effects and pairing phenomena.

Contribution

The study introduces a modified Skyrme density functional incorporating a pairing-related term, enhancing the description of charge radii and shell effects in nuclei.

Findings

Improved trend reproduction of differential charge radii along isotopic chains.

Prediction of shell quenching phenomena at specific neutron numbers.

Observation of inverted parabolic shapes between filled shells.

Abstract

A unified description of the charge radii throughout the entire nuclide chart plays an essential role for our understanding of nuclear structure and fundamental nuclear interactions. In this work, the influence of new term, which catches the spirit of neutron and proton pairs condensation around Fermi surface, on the charge radii has been investigated based on the Skyrme density functionals with the effective forces SLy5 and SkM$^{*}$. The differential charge radii of even-even Ca, Ni, Sn, and Pb isotopes are employed to evaluate the validity of this theoretical model. Meanwhile, the results obtained by the relativistic density functional with the effective Lagrangian NL3 are also shown for the quantitative comparison. The calculated results suggest that the modified model can improve the trend of changes of the differential charge radii along Ca, Ni, Sn, and Pb isotopic chains, especially the shell closure effect at the neutron numbers $N=28$, 82 and 126. The shell quenching phenomena of charge radii can also be predicted at the neutron number $N=50$ along the corresponding Ni and Sn isotopes, respectively. The inverted parabolic-like shapes between the two fully filled shells can also be observed, but the amplitude is gradually weakened from Ca to Pb isotopic chains. Combining the existing literatures, it suggests that the discontinuous behavior in nuclear charge radii can be described well by considering the influence of neutron Cooper pairs condensation around Fermi surface.