Interaction cross sections and matter radii of A=20 isobars

High-energy interaction cross sections of A = 20 nuclei (N-20, O-20, F-20, Ne-20, Na-20, Mg-20) on carbon were measured with accuracies of approximate to 1%. The nuclear matter r.m.s. radii derived from the measured cross sections show an irregular dependence on isospin projection. The largest difference in radii, which amounts to approximately 0.2 fm, has been obtained for the mirror nuclei O-20 and Mg-20. The influence of nuclear deformation and binding energy on the radii is discussed. By evaluating the difference in r.m.s. radii of neutron and proton distributions, evidence has been found for the existence of a proton skin for Mg-20 and of a neutron skin for N-20.