Dynamical evolution of the 197Au + 197Au system at 15 MeV/nucleon

Collisions of a very heavy Au-197 + Au-197 system have been studied at an energy of 15 MeV/nucleon with the aim to investigate a possible change of the energy dissipation mechanism from one-body dissipation (presumably dominating at low excitation energies) to two-body dissipation. The experiment was carried out in 4 pi geometry using the CHIMERA multidetector array. A class of ternary events satisfying nearly complete balance of mass numbers was selected. Preliminary results suggest that the selected ternary events represent mostly prompt ternary partitions of the colliding system, in which the lightest fragment is quite massive. In the light of theoretical predictions of Carjan, Sierk and Nix this result may imply that the observed ternary reactions are driven by the two-body dissipation mechanism already at 15 MeV/nucleon.