Unexpectedly large charge radii of neutron-rich calcium isotopes

TL;DR

This paper reports the first measurements of charge radii for neutron-rich calcium isotopes 49, 51, and 52, revealing unexpectedly large sizes that challenge existing nuclear models and the doubly-magic nature of 52Ca.

Contribution

It provides new experimental data on charge radii of calcium isotopes and compares them with advanced theoretical calculations, highlighting unexpected size increases.

Findings

Charge radii of 49, 51, 52Ca measured for the first time.

Large increase in size of neutron-rich calcium isotopes beyond N=28.

Challenges the doubly-magic nature of 52Ca.

Abstract

Despite being a complex many-body system, the atomic nucleus exhibits simple structures for certain "magic" numbers of protons and neutrons. The calcium chain in particular is both unique and puzzling: evidence of doubly-magic features are known in 40,48Ca, and recently suggested in two radioactive isotopes, 52,54Ca. Although many properties of experimentally known Ca isotopes have been successfully described by nuclear theory, it is still a challenge to predict their charge radii evolution. Here we present the first measurements of the charge radii of 49,51,52Ca, obtained from laser spectroscopy experiments at ISOLDE, CERN. The experimental results are complemented by state-of-the-art theoretical calculations. The large and unexpected increase of the size of the neutron-rich calcium isotopes beyond N = 28 challenges the doubly-magic nature of 52Ca and opens new intriguing questions on the evolution of nuclear sizes away from stability, which are of importance for our understanding of neutron-rich atomic nuclei.