Surprising charge-radius kink in the Sc isotopes at N=20

TL;DR

This paper reports the discovery of an unexpected charge-radius kink at N=20 in Sc isotopes, challenging existing nuclear shell models and highlighting unique structural effects in neutron-deficient nuclei.

Contribution

It provides new charge radii measurements for 40Sc and 41Sc, revealing a unique kink at N=20 not seen in neighboring elements, and questions current theoretical explanations.

Findings

Charge radii of 40Sc and 41Sc measured using laser spectroscopy

A pronounced charge-radius kink at N=20 in Sc isotopes observed

Existing models fail to explain the observed trend

Abstract

Charge radii of neutron deficient 40Sc and 41Sc nuclei were determined using collinear laser spectroscopy. With the new data, the chain of Sc charge radii extends below the neutron magic number N=20 and shows a pronounced kink, generally taken as a signature of a shell closure, but one notably absent in the neighboring Ca, K and Ar isotopic chains. Theoretical models that explain the trend at N=20 for the Ca isotopes cannot reproduce this puzzling behavior.