We revisit the studies of the isotopic shift in the charge radii of even–even isotopes of Sn and Pb nuclei at N = 82, and 126, respectively, within the relativistic mean-field (RMF) and relativistic-Hartree–Bogoliubov (RHB) approach. The shell model is also used to estimate isotopic shift in these nuclei, for the first time, to the best of our knowledge. The ground state single-particle energies (SPEs) are calculated for non-linear NL3 and NL3* and density-dependent DD-ME2 parameter sets compared with the experimental data, wherever available. We establish a correlation between the filling of single-particle levels and the isotopic shift in occupation probabilities. The obtained SPE from the RMF and RHB approaches are in line with those used in the shell model and experimental data for both the Sn and Pb isotopic chains. The shell model calculated isotopic shift agrees with RMF and RHB approaches that explain the experimental data quite well in case the of Pb nuclei beyond N=126.

我们重新审视了N处 Sn 和 Pb 核的偶偶同位素电荷半径的同位素位移研究在相对论平均场 (RMF) 和相对论-Hartree-Bogoliubov (RHB) 方法中，分别 = 82 和 126。据我们所知，壳模型还首次用于估计这些原子核的同位素位移。基态单粒子能量 (SPE) 是针对非线性 NL3 和 NL3* 以及与密度相关的 DD-ME2 参数集计算的，与实验数据相比，只要可用。我们建立了单粒子水平的填充与占领概率的同位素变化之间的相关性。从 RMF 和 RHB 方法获得的 SPE 与壳模型中使用的那些以及 Sn 和 Pb 同位素链的实验数据一致。N = 126。