Liquid-gas phase transition in nuclear matter

Every self-bound Fermi liquid will exhibit a liquid-gas phase equilibrium at low temperatures, because the pressure is positive at low densities due to the kinetic energy of degeneracy, and falls to zero again at the equilibrium density. Nuclear matter is seldom found under conditions of two-phase equilibrium, however: in usual nuclear reactions, a heated (`compound') nucleus is produced out of equilibrium with its surroundings, which are at a much lower temperature. The most familiar example of a two-phase equilibrium occurs in the crust of neutron stars inside the neutron-drip line¹, at temperatures of less than an MeV. In supernovas, in the crucial moments when the implosion is reversed to an explosion, densities comparable to those of neutron stars may be attained with associated temperatures of 5 to 10 MeV. An accurate knowledge of the properties of nuclear matter under these conditions is essential to the understanding of supernova dynamics². This communication shows how laboratory observations with the latest generation of nuclear accelerators can be used to infer the surface tension of the liquid-gas interface in nuclear matter-an essential ingredient of the equation of state for which a reliable theoretical model is not available.