Shell and isospin effects in nuclear charge radii

The shell effect and isospin effect in nuclear charge radii are systematically investigated and a four-parameter formula is proposed for the description of the root-mean-square (rms) charge radii by combining the shell corrections and deformations of nuclei obtained from the Weizs\"acker-Skyrme mass model. The rms deviation with respect to the 885 measured charge radii falls to 0.022 fm. The proposed formula is also applied for the study of the charge radii of super-heavy nuclei and nuclear symmetry energy. The linear relationship between the slope parameter L of the nuclear symmetry energy and the rms charge radius difference of 30S - 30Si mirror pair is clearly observed. The estimated slope parameter is about $L=54 \pm 19$ MeV from the coefficient of the isospin term in the proposed charge radius formula.