Collective dyanamics of intermediate-energy heavy-ion collisions

Exclusive measurements of massive projectile-like fragments (PLF), intermediate-mass fragments (IMF), light charged particles (lcp), and neutrons have been performed for the reactions 209Bi + 136Xe and 197Au+208Pb at the lower boundary (∼29MeV/u) of the Fermi energy regime. Unexpectedly, the measurements provide compelling evidence for very simple reaction dynamics dominated by collective degrees of freedom. Invariant emission patterns of neutrons or lcp's indicate a binary first reaction stage, followed by the decay of the hot reaction products, for essentially the entire range of impact parameters. Non-evaporative light particles and cold IMF's are observed in peripheral collisions. IMF's seen in 209Bi + 136Xe collisions are possibly due to non-adiabatic neck rupture. Experimental correlations between particle multiplicity, and massive-fragment energy, deflection angle, and Z distribution suggest the presence of exchange-induced transport phenomena. In both reactions, the initially available kinetic energy is only partially damped. Together, these new observations challenge the present paradigm