Neutron density distributions from antiprotonic Pb208 and Bi209 atoms

Abstract

The x-ray cascade from antiprotonic atoms was studied for Pb208 and Bi209. Widths and shifts of the levels due to the strong interaction were determined. Using modern antiproton-nucleus optical potentials, the neutron densities in the nuclear periphery were deduced. Assuming two-parameter Fermi distributions (2pF) describing the proton and neutron densities, the neutron rms radii were deduced for both nuclei. The difference of neutron and proton rms radii Δrnp equal to 0.16±(0.02)stat±(0.04)syst fm for Pb208 and 0.14±(0.04)stat±(0.04)syst fm for Bi209 were determined, and the assigned systematic errors are discussed. The Δrnp values and the deduced shapes of the neutron distributions are compared with mean field model calculations. © 2007 The American Physical Society.