Entrance channel dependence of quasifission in reactions forming 220Th

Mass-angle correlations of binary fragments produced in O-16+Pb-204, S-34+W-186, and Ti-48,Ti-50+Er-166,Er-170 reactions have been measured for a range of bombarding energies around their Coulomb barriers. At above-barrier energies, the width of the mass distributions for the fission-like fragments in the Ti-50+Er-170 reaction are found to be higher than those from the same compound system at similar excitation energies populated via the more mass asymmetric entrance channel reaction S-34+W-186, which in turn is higher than those for the O-16+Pb-204 system. The width of the mass distributions of the Ti + Er systems is found to increase with decreasing bombarding energies, in contrast with those of the O-16+Pb-204 and S-34+W-186 systems, which show a monotonic reduction in mass widths. This may be associated with the elongated contact configuration at sub-barrier energies.