Swelling of doubly magic $^{48}$Ca core in Ca isotopes beyond $N=28$

TL;DR

This study measures interaction cross sections of calcium isotopes beyond N=28, revealing a significant increase in matter radii and neutron skin thickness, indicating core swelling of $^{48}$Ca in these isotopes.

Contribution

First measurement of interaction cross sections for Ca isotopes beyond N=28, demonstrating core swelling and increased neutron skin thickness through combined experimental and theoretical analysis.

Findings

Matter radii increase beyond N=28

Neutron skin thickness grows significantly

Core swelling of $^{48}$Ca inferred

Abstract

Interaction cross sections for $^{42\textrm{-}51}$Ca on a carbon target at 280 MeV/nucleon have been measured for the first time. The neutron number dependence of derived root-mean-square matter radii shows a significant increase beyond the neutron magic number $N=28$. Furthermore, this enhancement of matter radii is much larger than that of the previously measured charge radii, indicating a novel growth in neutron skin thickness. A simple examination based on the Fermi-type distribution, and the Mean-Field calculations point out that this anomalous enhancement of the nuclear size beyond $N=28$ results from an enlargement of the core by a sudden increase in the surface diffuseness of the neutron density distribution, which implies the swelling of the bare $^{48}$Ca core in Ca isotopes beyond $N=28$.