Liquid-gas phase instabilities and droplet formation in nuclear reactions

Abstract

The thermodynamics and critical exponents of nuclear matter near the critical point of a liquid-gas phase transition are studied. We then investigate fluctuations near the critical point. One effect of a finite number of nucleons, as in nuclear reactions, is to wash out the first-order phase transition for several MeV below the critical temperature. This is manifested in the fact that there is a finite probability for the system to exist in the metastable or unstable regions of infinite matter. The phenomenological droplet model is applied to a wide range of recent data on fragment yields in the range $6<A<52$, and good fits are obtained. Heavy ion reactions are consistent with droplet formation in a supersaturated vapor, with supersaturation ratios up to 3.25. Proton-nucleus reactions are consistent with droplet formation in a saturated vapor.