Entrance-channel effects in quasifission reactions

The entrance-channel dependence of the distribution of reaction strength has been studied for three systems, namely $^{32}\mathrm{S}$${+}^{182}$W, $^{48}\mathrm{Ti}$${+}^{166}$Er, and $^{60}\mathrm{Ni}$${+}^{154}$Sm, which all lead to the compound system $^{214}\mathrm{Th}$ in complete fusion reactions. The cross sections for elastic/quasielastic scattering, deeply inelastic, and fissionlike processes were measured at beam energies of ${\mathit{E}}_{\mathrm{lab}}$ =166, 177, 222, 260 MeV for $^{32}\mathrm{S}$${+}^{182}$W, ${\mathit{E}}_{\mathrm{lab}}$=220, 240, 270, 298 MeV for $^{48}\mathrm{Ti}$${+}^{166}$Er, and ${\mathit{E}}_{\mathrm{lab}}$=339, 390, 421 MeV for $^{60}\mathrm{Ni}$${+}^{154}$Sm, respectively. The maximum contribution of complete-fusion fission processes to the fissionlike cross section is estimated on the basis of expected angle-mass correlations for such reactions. The results show a strong entrance-channel dependence as predicted by the extra-push model. \textcopyright{} 1996 The American Physical Society.