Primary mass and charge distributions in the reaction of 900 MeV 132Xe ions with 197Au

A stacked foil technique and radioehemical yield measurements were combined in order to study the reaction of ¹³²Xe ions with ¹⁹⁷Au at 1.3 times the interaction barrier energy. Evidence is presented for a preferential exchange of neutrons for energy losses of up to 100 MeV. The same amount of energy damping is required for the development of a drift in the position of the centroid of the element distribution and for the evolution of full correlations in the exchange of neutrons and protons. The widths of the charge distributions at fixed mass asymmetry rise slowly as the degree of energy damping increases. This is reminiscent of classical statistical fluctuations, although the widths at large excitation energies have also been reproduced quantum-mechanically in terms of the zero-point motion of a collective isovector mode analogous to the giant dipole resonance in spherical nuclei. All results concerning the initial evolution of charge and mass distributions seem to be dominated by a hindrance of proton exchanges for large internuclear distances.