Complete fusion cross sections have been determined by directly detecting evaporation residuals for the systems ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ + ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ + ${}_{}{}^{28,30}{}_{}{}^{}\mathrm{Si}$ over a ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ laboratory energy range 34-75 MeV. In all cases ${\sigma }_{\mathrm{fus}}$ increases smoothly with energy and eventually saturates at 1200-1250 mb. In the barrier penetration region the cross section for ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ is always sufficiently smaller than that for ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ + ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$ to make the reduced barrier radius in a Glas-Mosel parametrization significantly smaller for the former system than for the latter. Three entrance channels are now available for the fused-system ${}_{}{}^{46}{}_{}{}^{}\mathrm{Ti}$: Critical angular momentum data from the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$ entrance channel approach the statistical yrast line at much lower fused-system excitation energy than do the data from the entrance channels ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ + ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$.

NUCLEAR REACTIONS Measured complete fusion cross sections for the systems ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ + ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ + ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$; $E=34-75\mathrm{}$ MeV. Deduced Glas-Mosel model and statistical yrast model parameters.

• Received 10 August 1981

DOI:https://doi.org/10.1103/PhysRevC.24.2507