Multifragmentation of gold nuclei by light relativistic ions: thermal breakup versus dynamical disintegration

The multiple emission of intermediate-mass fragments (IMF) is studied for c ollisions of p, He-4, and C-12 on Au with the 4 pi FASA setup. The mean mul tiplicities of IMF saturate at a value of around 2 for incident energies ab ove 6 GeV. An attempt at describing the observed IMF multiplicities in the two-stage scenario, a fast cascade followed by a statistical multifragmenta tion, fails. Agreement with the measured IMF multiplicities is obtained by introducing an intermediate expansion phase and modifying empirically the e xcitation energies and masses of remnants. The angular distributions and en ergy spectra from p-induced collisions are in agreement with the scenario o f "thermal" multifragmentation of a hot and expanded target spectator. In t he case of C-12 + Au (22.4 GeV) and He-4 (14.6 GeV) + Au collisions, deviat ions from a pure thermal breakup are seen in the fragment energy spectra, w hich are harder than those both from model calculations and from the measur ed ones for p-induced collisions. This difference is attributed to a collec tive flow with the expansion velocity at the surface of about 0.1c (for C-1 2 + Au collisions). (C) 2001 MAIK 'Nauka/Interperiodica".