Evidence for diffusive relaxation along the mass asymmetry coordinate in the reaction 197Au + 620 MeV 86Kr

Abstract

Nuclei have been identified by atomic number up to Z = 50 using ΔE- E telescopes. Kinetic energy spectra, charge and angular distributions have been measured from θ lab = 10–80° . At angles removed from the grazing, a single peak with a mean energy somewhat below the calculated Coulomb energy is observed for all elements. Near the grazing angle, a much broader peak appears, which extends from near elastic energies down to the Coulomb barrier. The charge distributions are peaked near the projectile Z and demonstrate a strong shape dependence on the angle of observation. The angular distributions for elements near the projectile are strongly side peaked; however, as Z is increased or decreased from Z = 36, they gradually become forward peaked. The dependence of the charge and angular distributions on energy dissipation is discussed as well as the patterns observed in the two-dimensional Wilczynski plots. Diffusion model calculations reproduce the experimental data both qualitatively and quantitatively. This successful application of the diffusion model, which was originally developed to explain N, Ne and Ar induced reactions, to the present system is strong evidence that no essential differences exist between the “quasi-fission” process observed in Kr bombardments of heavy targets and the deep-inelastic phenomena seen with lighter ions.