  We study theoretically how we can determine the neutron density distributions
of unstable nuclei from proton elastic scattering. We apply the relativistic
impulse model to study the sensitivities of the observables to the density
distributionswhich are expressed in Woods-Saxon form. We find that the both
radius and diffuseness of densities can be determined from restricted elastic
scattering data in principle. We think this result is helpful to design future
experiments.
