Spinodal decomposition of expanding nuclear matter and multifragmentation

Density fluctuations of expanding nuclear matter are studied within a mean-field model in which fluctuations are generated by an external stochastic field. The time evolution of the system is studied in a kinetic-theory approach. In this model, fluctuations develop about a mean one-body phase-space density corresponding to a hydrodynamic motion that describes a slow expansion of the system. A fluctuation-dissipation relation suitable for a uniformly expanding medium is obtained and used to constrain the strength of the stochastic field. The coupling between the kinetics of fluctuations and the hydrodynamic expansion is analyzed, and the distribution of the liquid domains in the spinodal decomposition of this expanding nuclear matter is derived. It is found that the formation of the domains can be envisaged as a stationary process. Comparison of the related distribution of the fragment size with experimental data on the nuclear multifragmentation is quite satisfactory.