Charge radii in covariant density functional theory: a global view*

A systematic global investigation of differential charge radii has been performed within the covariant density functional theory

framework for the first time. Theoretical results are compared with experimental differential

charge radii in the regions of the nuclear chart in which available experimental data crosses neutron

shell closures at N = 28, 50, 82 and 126. The analysis of absolute differential radii of diferent isotopic

chains and their relative properties indicate clearly that such properties are reasonably well described

in model calculations in the cases when the mean-field approximation is justified.

It is shown that the kinks in the charge radii at neutron shell closures

are due to the underlying single-particle structure and due to weakening or collapse of pairing at

these closures. It is usually assumed that pairing is a dominant contributor

to odd-even staggering (OES) in charge radii. Our analysis paints a more complicated picture. It

suggests a new mechanism in which the fragmentation of the single-particle content of the ground

state in odd-mass nuclei due to particle-vibration coupling provides a significant contribution to

OES in charge radii. The relative energies of the single-particle states and the patterns of their occupation with increasing

neutron number have an appreciable impact on the evolution of the differential charge radii. These factors also

limit the predictive power of model calculations in the regions of high densities of the single-particle

states. The regions of the nuclear chart in which the correlations beyond mean field are

expected to have an impact on charge radii are indicated. However, the assignment

of a calculated excited  minimum to the experimental ground states allows to understand

the trends of the evolution of differential charge radii with neutron number in these cases.