Entrance-channel effects in quasifission reactions

The entrance-channel dependence of the distribution of reaction strength has been studied for three systems, namely ³²S+¹⁸²W, ⁴⁸Ti+¹⁶⁶Er, and ⁶⁰Ni+¹⁵⁴Sm, which all lead to the compound system ²¹⁴Th in complete fusion reactions. The cross sections for elastic/quasielastic scattering, deeply inelastic, and fissionlike processes were measured at beam energies of E_lab =166, 177, 222, 260 MeV for ³²S+¹⁸²W, E_lab=220, 240, 270, 298 MeV for ⁴⁸Ti+¹⁶⁶Er, and E_lab=339, 390, 421 MeV for ⁶⁰Ni+¹⁵⁴Sm, 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. © 1996 The American Physical Society.