Fine structure in the mass number dependence of rms charge radii

A comprehensive study of experimental rms charge radii shows that the deviation from the rough $\text{A}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ dependence follows simple trends. For the isotopic sequence of an element, the values of rms radii, normalized by an approximate $\text{A}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ law and plotted as a function of neutron number, lie on or close to straight lines. The slopes of these lines vary systematically as a function of atomic number. There are discontinuities in the values of the slopes for elements that contain N = 20, 28, 50, 82, 88, 90 and 126 neutrons as well as between Z = 8 and 10; a significant change can be found also for the region Z = 76 (N ≈ 114). These changes can be explained qualitatively by the shell model and by the effect of deformation. An “odd-even staggering” of the order of 6 × 10^?4 has also been observed.