Nuclear periphery studied with antiprotonic atoms

Abstract

Two experimental methods were employed to study the nuclear peripheral density. The first method was based on antiprotonic X ray measurements. The widths and shifts of the last atomic state levels available for the antiproton were deduced from the shape of the X-ray lines. These observables are sensitive to the nuclear matter density at a distance 1.5 fm larger than the charge half-density radius. The other method consisted in studying the antiproton annihilation products and gave information on the neutron-to-proton density ratio at a radius 2.5 fm larger than the charge half-density radius. This article presents the results obtained by the PS209 collaboration in measurements performed with the LEAR facility at CERN. Neutron densities and differences of neutron and proton root-mean-square radii were deduced for isotopes over a wide mass range (A = 40–238).