Isospin Lattice Gas Model and Nuclear-Matter Phase Diagram and Pressure-Volume Isotherms

We study a cubic lattice gas model for nuclear matter where each lattice site can be either occupied, by one proton or one neutron, or unoccupied. A nearest-neighbor interaction of the form $ - \sum_{<ij>} J_{ij}\tau_{zi} \tau_{zj}$ is assumed. Our model is an isospin-1 Ising model, with ${\tau_z}$ = (1,0,-1) representing respectively (proton, vacancy, neutron). A kinetic-energy term has been included in our model. Under the Bragg-Williams mean field approximation our model exhibits the existence of a dense phase (liquid-like) and a rare phase (gas-like). The nuclear-matter p-v isotherms given by our model are discussed.