On the way from thermal multifragmentation to dynamical disintegration

Multiple emission of intermediate-mass fragments has been studied for the c ollisions of p, He-4 and C-12 On Au with the 4 pi setup FASA. In the case o f C-12(22.4 GeV)+Au and He-4(14.6 GeV)+Au collisions, the deviations from a pure thermal break-up are seen in the energy spectra of the emitted fragme nts, which are harder than those both from model calculations and from meas ured p-induced collisions. This difference is attributed to a collective fl ow with an expansion velocity at the surface about 0.1 c (for C-12+Au colli sions).