FLUCTUATIONS AND INSTABILITIES IN MULTIFRAGMENTATION

In this article we review the foundations of dynamical description of unstable systems. We describe the concept of stochastic one-body theor ies. In particular, spinodal instabilities are accounted for: the most unstable modes which depend mostly on the range of the nuclear force are shown to determine the early unstable dynamics and therefore the i nitial multifragmentation; the characteristic time scales for the grow th of these modes and the typical time scales for cluster formation, a s a function of the amplitude of fluctuations, are discussed. The diff erences between such a fragmentation pattern, essentially determined b y the instabilities, and fragmentation structures obtained from the hy pothesis of statistical equilibrium are stressed. Finally, we propose that the occurrence of spinodal instabilities can be signed by a lack of small size fragments associated to a tendency to break the system i n close-mass pieces.