Neutron-skin and proton-skin formations in exotic nuclei far from stability

The neutron skin is studied in terms of the Hartree-Fock calculation, and its new definition is presented and discussed. It turns out that the neutron skin is closely related to how far the nucleus is away from the β stability line, but not directly to the number of excess neutrons. Related properties of Hartree-Fock calculations for unstable nuclei are discussed. Novel features associated with the neutron skin are suggested, for instance, neutron avalanche in reactions involving a nucleus with the neutron skin. The formation of the proton skin is shown to be rather difficult.