Evaporation residues resulting from the ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$${+}^{27}$Al and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$${+}^{19}$F fusion reactions leading to the ${}_{}{}^{38}{}_{}{}^{}\mathrm{Ar}$ compound nucleus and from the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$+${(}^{12}$C, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$) reactions have been measured at incident energies 32 MeV≤${\mathit{E}}_{\mathit{L}}$${(}^{19}$F)≤72 MeV and 15 MeV≤${\mathit{E}}_{\mathit{L}}$${(}^{11}$B)≤50 MeV. The hindrance of the fusion cross sections, at energies above the interaction barrier, show a clear dependence on the entrance channel mass asymmetry. This dependence is discussed in terms of model predictions that treat explicitly the mass asymmetry degree of freedom.

• Received 6 December 1989

DOI:https://doi.org/10.1103/PhysRevC.42.354