Nuclear matter properties, phenomenological theory of clustering at the nuclear surface, and symmetry energy

TL;DR

This paper develops a phenomenological model of nuclear matter incorporating clustering at the surface, explaining large symmetry energy values and connecting nuclear matter properties with finite nuclei, with implications for neutron skin thickness.

Contribution

It introduces a unified framework linking clustering effects in nuclear matter and finite nuclei using an extended Thomas-Fermi approach, including realistic equations of state and pairing effects.

Findings

Large symmetry energy at low densities explained by clustering.

Neutron skin thickness reduced due to clustering effects.

Predictions for new regimes in nuclear matter and nuclei.

Abstract

We present a phenomenological theory of nuclei that incorporates clustering at the nuclear surface in a general form. The theory explains the recently extracted large symmetry energy by Natowitz et al. at low densities of nuclear matter and is fully consistent with the static properties of nuclei. In phenomenological way clusters of all sizes, shapes along with medium modifications are included. Symmetric nuclear matter properties are discussed in detail. Arguments are given that lead to an equation of state of nuclear matter consistent with clustering in the low density region. We also discuss properties of asymmetric nuclear matter. Because of clustering, an interesting interpretation of the equation of state of asymmetric nuclear matter emerges. As a framework, an extended version of Thomas Fermi theory is adopted for nuclei which also contain phenomenological pairing and Wigner contributions. This theory connects the nuclear matter equation of state, which incorporate clustering at low densities, with clustering in nuclei at the nuclear surface. Calculations are performed for various equation of state of nuclear matter. We consider measured binding energies of 2149 nuclei for N, Z \geq 8. The importance of quartic term in symmetry energy is demonstrated at and below the saturation density of nuclear matter. It is shown that it is largely related to the use of, ab initio, realistic equation of state of neutron matter, particularly the contribution arising from the three neutron interaction and somewhat to clustering. Reasons for these are discussed. Because of clustering the neutron skin thickness in nuclei is found to reduce significantly. Theory predicts new situations and regimes to be explored both theoretically and experimentally.