Charge Radii of Neutron-Rich Scandium Isotopes and the Seniority Symmetry in the 0f7/2 Shell

Nuclear charge radii of neutron-rich Sc47–49 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 Sc41 and Sc49 isotopes having similar values, mirroring the closeness of the charge radii of Ca40 and Ca48. 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 Sc49 radius data has unveiled a similar trend in the charge radii of N=28 isotones and Z=20 isotopes when adding the protons atop the Ca48 core and the neutrons atop the Ca40 core, respectively. We demonstrate that this trend is consistent with the prediction of the seniority model. Published by the American Physical Society 2025