Incomplete Fusion and Cluster Production In Heavy-ion Collisions At 30 Mev Nucleon

The total energy dissipated in central collisions has been measured for the system S-32 + Ni-58 at about 1 GeV incident energy. An event-by-event reconstruction of the atomic charge of the reaction products was performed by means of a 4-pi charged-particle detector. Two distinct classes of events were thus separated: one consistent with a "conventional" incomplete fusion-evaporation process, a second where three or more heavy fragments are produced. A subtraction of the evaporative component from the particle spectra at all angles allowed extraction of the excitation energy removed from the system by pre-equilibrium emission. The average excitation energies corresponding to the two different classes of events were determined. Comparisons with statistical model calculations as well as a multifragmentation model are presented.