Fusion suppression in mass-asymmetric reactions leading to Ra compound nuclei

Near-barrier excitation functions have been measured for evaporation-residue production and fission in the ${}^{12}\mathrm{C}{+}^{204,206,208}\mathrm{Pb}$ and ${}^{48}\mathrm{Ca}{+}^{168,170}\mathrm{Er}$ systems that lead to the compound nuclei ${}^{216,218,220}{\mathrm{Ra}}^{*}.$ A pronounced suppression of evaporation-residue production is observed for the more symmetric combinations, ${}^{48}\mathrm{Ca}{+}^{168,170}\mathrm{Er}.$ We relate this to the significant quasifission components already observed for these systems.