Surface Symmetry Energy

The symmetry term in the standard semiempirical formula for binding energy has a volume character. However, as we demonstrate, the description of binding energies for light nuclei requires an inclusion of the surface symmetry energy in the binding-energy formula. The symmetry volume and surface energies combine in the formula like energies of two capacitors in parallel. A finite surface symmetry energy necessarily implies the existence of nuclear asymmetry skins, describable in terms of the ratio of symmetry energy volume parameter alpha to an analogous surface parameter beta. Using available binding energy and skin data, we constrain the parameter values, finding 27MeV< alpha < 32MeV and 10.0MeV< beta <12.5MeV. We demonstrate in the Thomas-Fermi theory that the emergence of surface symmetry energy is related to the drop of symmetry energy per nucleon S with density and we constrain that drop, at half of the normal density rho_0, to 0.56< S(rho_0/2)/S(rho_0)