Neutron distributions from pionic atoms

The radii of neutron distributions in nuclei are extracted from experimental shifts and widths of pionic atoms. A best fit to pionic-atom data is carried out by varying simultaneously the neutron radii and the parameters of a pion-nucleus optical potential. We have used three different potentials: one of them theoretical plus a small phenomenological part, another one semiphenomenological, with the linear terms in the density obtained from experimental πN amplitudes and the quadratic terms fitted to the pionic-atom data, and a third one purely phenomenological, obtained from a direct fit to pionic-atom data. The radii obtained with all of them are remarkably close and also close to the Hartree-Fock values. The combined statistical and systematic errors of the neutron mean-root-square radii are smaller than 0.2 fm for light and medium nuclei and smaller than 0.1 fm for heavy model. (orig.)