Clustering at the nuclear surface and symmetry energy

Abstract

With in the energy density functional formalism a phenomenological theory of nuclei is developed which incorporates clustering at the nuclear surface in a general form. This explains the large values of symmetry energy extracted recently at low values of nuclear matter density. It is shown that the nuclear matter binding energy per nucleon (B/A), in the neighbourhood of zero density, must approach its value at the saturation density. The parameters of the theory are mainly constrained from the binding energies and root mean square radii of 376 spherical nuclei as well as the large values of the recently extracted symmetry energy at low densities. Importance of quartic term in symmetry energy is demonstrated. It is shown that it originates due to clustering as well as due to contribution of three-nucleon interaction in the state-of-the-art equation of state of neutron matter at and below the saturation densities. It is found that clustering significantly reduces the neutron skin thickness in nuclei.