  In the present work, we study the experimental data on the root mean square
charge radii of the spherical atomic nuclei. The purpose of this analysis is to
clarify what is the manifestation of the neutron shells in the considered
observable and to find regularities in the behavior of the charge radii when a
shell neutron is crossed. As the result, we have found manifestations of the
shells N_sh=8,28,50 and 82. It turns out that the well-known shells with the
neutron numbers 20 and 126 do not show up. The present analysis is performed by
means of the relative charge radius x(N,N_sh,Z). This value is equal to the
charge radius of a given isotope over the charge radius of the isotope of the
given element with the closed neutron shell. It is shown that the values of x
form groups corresponding to different values of N_sh. Prediction for unknown
charge radius of sulfur-30 has been made.
