Dynamical approaches to cluster formation and nuclear multifragmentation

Multifragmentation in heavy-ion collisions is interpreted as a consequence of a first-order liquid-gas phase transition in expanding nuclear matter. In contrast to widely found attempts, it is shown that Fisher's model is, in general, not applicable for the analysis of experimental results concerning the shape of intermediate mass fragment (IMF) distributions. It may be valid only provided the fragmentation proceeds in the immediate vicinity of the liquid-gas critical point of nuclear matter but not in the thermodynamically metastable or unstable regions beyond it. But even in the vicinity of the critical point its applicability is questionable by different reasons one of them being the static nature of the model. Beyond the liquid-gas critical point, IMF size distributions of the shape N(A) proportional to A(-tau) may be explained straightforwardly based on a dynamic model of clustering in expanding nucleonic matter. This model leads to qualitatively similar results widely independent on the initial excitation energy of the nucleonic system. In dependence of the initial conditions the parameter tau may vary hereby in the range from 2 less than or equal to r less than or equal to 6. Moreover, the model allows also to explain straightforwardly deviations from such a simple picture and the origin for them.