Based on a relativistic Thomas–Fermi model, it is shown that a two-parameter Fermi distribution can be used for describing the neutron density distribution in the 208 Pb nucleus.
In heavy nuclei the spatial distribution of protons and neutrons is different. At CERN SPS energies production of π+ and π- differs for pp, pn, np and nn scattering. These two facts lead to an impact parameter dependence of the π+ to π- ratio in 208Pb+208Pb collisions. A recent experiment at CERN seems to confirm qualitatively these predictions. It may open a possibility for determination of neutron density distribution in nuclei.