Charge radii of neutron-rich scandium isotopes and the seniority symmetry in the $0f_{7/2}$ shell

Abstract

Nuclear charge radii of neutron-rich ${}^{47-49}$Sc isotopes were measured using collinear laser spectroscopy at CERN-ISOLDE. The new data reveal that the charge radii of scandium isotopes exhibit a distinct trend between $N=20$ and $N=28$, with ${}^{41}$Sc and ${}^{49}$Sc isotopes having similar values, mirroring the closeness of the charge radii of ${}^{40}$Ca and ${}^{48}$Ca. Theoretical models that successfully interpret the radii of calcium isotopes could not account for the observed behavior in scandium radii, in particular the reduced odd-even staggering. Remarkably, the inclusion of the new ${}^{49}$Sc radius data has unveiled a similar trend in the charge radii of $N=28$ isotones and $Z=20$ isotopes when adding the neutrons atop the ${}^{40}$Ca core and the protons atop the ${}^{48}$Ca core, respectively. We demonstrate that this trend is consistent with the prediction of the seniority model.

Comments: Version accepted for publication in Phys. Rev. Lett