The peripheral neutron distribution in stable nuclei deduced from antiprotonic atoms

Two kinds of experiments using an antiproton beam were performed to investigate the nuclear periphery: the on-line measurement of antiprotonic X-rays and the off-line determination of the yield of annihilation products with mass number one unit smaller than the target mass. The neutron-to-proton density ratios as well as the differences of root-mean-square (rms) radii of neutron and proton distributions were determined for a number of stable isotopes. To this end both the neutron and the proton density distributions were assumed to have the form of a two-parameter Fermi distribution. The differences of rms radii are caused mostly by an increase in the neutron diffuseness and not in half-density radius. The results agree with corresponding data derived by other methods and with theoretical predictions.