Evaporation residue cross sections for ${}^{28}\mathrm{Si}{+}^{198}\mathrm{Pt}$ and ${}^{76}\mathrm{Ge}{+}^{150}\mathrm{Nd},$ both of which form a compound nucleus ${}^{226}\mathrm{U},$ were measured in the vicinity of the Coulomb barrier. The measurement gives direct evidence that the system really fuses together to form a fully equilibrated compound nucleus. For the ${}^{28}\mathrm{Si}{+}^{198}\mathrm{Pt}$ reaction, we have measured the fission fragments to determine the fusion cross section by taking advantage of the highly fissile character of ${}^{226}\mathrm{U}.$ The evaporation residue cross section and the fusion cross section for ${}^{28}\mathrm{Si}{+}^{198}\mathrm{Pt}$ allowed us to investigate the deexcitation process (exit channel) of the compound nucleus ${}^{226}\mathrm{U},$ and the parameters entering in a statistical model calculation could be determined. By estimating the deexcitation of the compound nucleus ${}^{226}\mathrm{U}$ with the statistical model, the effect of the deformed nucleus ${}^{150}\mathrm{Nd}$ on the fusion reaction ${}^{76}\mathrm{Ge}{+}^{150}\mathrm{Nd}$ was extracted. The experimental data indicated that there is more than 13 MeV extra-extra-push energy for the system to fuse together when the projectile ${}^{76}\mathrm{Ge}$ collides at the tip of the deformed ${}^{150}\mathrm{Nd}$ nucleus. On the contrary, for the side collision which is more compact in configuration than the tip collision, no fusion hindrance is suggested.

• Received 17 December 1999

DOI:https://doi.org/10.1103/PhysRevC.62.014602