Abstract
We have measured coincidences between and ,2,3H or a second (large-angle correlations) in the reactions 247 and 337 MeV ArAg. These coincidences are dominated by reactions leading to evaporation residues with spins of about 0–70ħ. Large values of the angle-integrated double and triple coincidence cross sections indicate that many particle evaporation chains involve 2 or 3 protons and/or 2 or 3 alphas. The angular and energy distributions are well described by an evaporation model with Hauser-Feshbach coupling. However, one must employ effective evaporation barriers for and that are strongly reduced compared to empirical fusion barriers. The barrier reduction required for is rather small, and for no barrier reduction is needed. Evaporation calculations that include emitter deformation do not give a satisfactory explanation for these results. We suggest a new aspect of composite nucleus excitation and evaporation-like decay. A hot, very diffuse nuclear surface may be formed that promotes evaporative decay prior to its relaxation. The low barriers for and reflect the radial extent of this transitory, diffuse surface.
- Received 11 February 1988
DOI:https://doi.org/10.1103/PhysRevC.37.2561
©1988 American Physical Society