  Charge density difference between 206Pb and 205Tl, measured by elastic
electron scattering, is very similar to the charge density due to a proton in a
3s1/2 orbit. We look for a potential well whose 3s1/2 wave function yields the
measured data. We developed a novel method to obtain the potential directly
from the density and its first and second derivatives. Fits to parametrized
potentials were also carried out. The 3s1/2 wave functions of the potentials
determined here, reproduce fairly well the experimental data within the quoted
errors. To detect possible effects of short-range two-body correlations on the
3s1/2 shell model wave function, more accurate measurements are required.
