Implication of shell quenching in scandium isotopes around <i>N</i>=20*

Abstract Shell closure structures are commonly observed phenomena associated with nuclear charge radii throughout the nuclide chart. Inspired by recent studies demonstrating that the abrupt change can be clearly observed in the charge radii of the scandium isotopic chain across the neutron number N =20, we further review the underlying mechanism of the enlarged charge radii for 42 Sc based on the covariant density functional theory. The pairing correlations are tackled by solving the state-dependent Bardeen-Cooper-Schrieffer equations. Meanwhile, the neutron-proton correlation around the Fermi surface derived from the simultaneously unpaired proton and neutron is appropriately considered in describing the systematic evolution of nuclear charge radii. The calculated results suggest that the abrupt increase in charge radii across the N =20 shell closure seems to be improved along the scandium isotopic chain if the strong neutron-proton correlation is properly included.