Investigation of the velocity distribution of evaporation residues produced in20Ne+197Au reactions atE/A=5.7–11.4 MeV/u

The velocity distributions of evaporation — residues produced in complete fusion reactions of²⁰Ne+¹⁹⁷Au at bombarding energies ofE/A=5.7, 8.6 and 11.4MeV/u were measured with use of the velocity filter SHIP. It could be shown, that the production cross section for evaporation residues is influenced by emission of fast, light particles having an angular distribution, that is peaked in forward direction (preequilibrium particles). This contribution is, however too small to explain the enhancement of the evaporation residue production cross section by about two orders of magnitude compared to statistical model calculations. This latter effect is interpreted as mainly due to a delayed onset of compound fission.