A study of diffusion phenomena in the rare earth region: The reaction 159Tb + 620 MeV 86Kr

Abstract

Kinetic energy spectra, charge and angular distributions have been measured with ΔE- E telescopes for over twenty-five identified elements from the reaction 159 Tb + 620 MeV 86 Kr . At all angles and for all observed atomic numbers, the energy spectra indicate the presence of energetically relaxed products in the vicinity of the Coulomb barrier. Elements near the projectile also show a sizable contribution from incompletely damped events at angles close to the grazing angle. The charge distributions are peaked near the projectile Z and demonstrate a strong shape dependence on the angle of observation. The angular distributions show a weakening of the side peaking with increasing proton transfer to or from the projectile. Angular distributions and angle-integrated charge distributions have been calculated with a diffusion model which assumes the formation of a rotating intermediate complex with an l-dependent lifetime. The mass exchange between the two segments of the intermediate complex is treated as a diffusive process which is described by the master equation. Values for the diffusion constant, the overlap of the two density distributions, the mean lifetime of the intermediate complex and the spread in the average lifetime were used which semiquantitatively reproduced data from the 620 MeV 86Kr reaction on 181Ta and 197Au targets. Satisfactory agreement was obtained between these calculations and the data from the 159Tb target. In addition, by increasing the lifetime of the complex by 30 %, the previously measured data for the 107, 109Ag + 620 MeV 86Kr reaction was semiquantitatively reproduced.