Isospin dependence of proton and neutron radii within relativistic mean field theory

The proton and neutron radii of even-even β-stable nuclei with A ⩾ 40 and a few chains of isotopes with Z = 50, 56, 82, 94 protons and isotones with N = 50, 82, 126 neutrons are analyzed. The average isospin dependence of the radii evaluated within the relativistic mean field theory is studied. A simple, phenomenological formula for neutron radii is proposed.