Chemical and mechanical instability in hot isospin - asymmetric nuclear matter

Using phenomenological equations of state, we study the chemical and mechanical instabilities in hot isospin-asymmetric nuclear matter. Both instabilities are found to depend strongly on the isospin asymmetry of the nuclear matter. For a chemically and mechanically stable asymmetric nuclear matter, a lower neutron excess is found in the liquid phase than in the gas phase. Furthermore, the neutron excess in the mixed phase at densities between that of the liquid and the gas phases is limited by certain maximum value. Also, for the nuclear equations of state considered here the boundary of chemical instability in the pressure-density plane is found to be more extended than that of mechanical instability. However, locations of these boundaries depend sensitively on both the bulk compressibility of nuclear matter and the density dependence of the symmetry energy.