Nuclear diffuseness as a degree of freedom

The response of the nuclear energy to changes in neutron and proton surface diffusenesses is investigated using the Thomas-Fermi model. Algebraic expr essions are provided for the energy cost of changing the two diffusenesses away from their equilibrium values. This will make it possible to generaliz e the macroscopic-microscopic calculations of nuclear masses and deformatio n energies by the inclusion of the neutron and proton diffusenesses as degr ees of freedom (to be varied along with the shape degrees of freedom). One result, which is suggested by the relatively low cost in macroscopic energy of increasing the diffuseness of a heavy nucleus by 10% (abour 4 MeV), is that superheavy nuclei near Z=126, N=184 may have a fair chance of becoming stabilized by shell effects. An appendix introduces an improved measure of surface diffuseness, with certain advantages over the conventional Sussman n width b. [S0556-2813(98)03612-7].