Evolutionary features of collisions between heavy ions at Fermi energies

Collisions between heavy ions in the domain of bombarding energies comparable to the nucleonic Fermi energy have been investigated experimentally and in simulation calculations. Exclusive measurements have been performed for the systems 197Au+208Pb, 209Bi+136Xe, 197Au+86Kr, and 112Sn+40,48Ca, where a range of light, intermediate-mass, and heavy charged products have been measured in coincidence with neutrons. Experimental deflection functions and primary atomic-number distributions have been deduced in several cases. In addition, the statistical emission and a new, very fast, dynamical production mechanism of intermediate-mass fragments have been followed as functions of the dissipated energy or impact parameter. Trajectory simulation calculations are consulted in attempts to explain the new IMF emission mechanism. Although similarities to the dissipative reaction mechanism have been observed, neither nucleon exchange nor BUU models give an adequate account of the reaction features, presenting challenges to modern reaction theory