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 ¹²C+204,206,208Pb and ⁴⁸Ca+168,170Er systems that lead to the compound nuclei 216,218,220Ra*. A pronounced suppression of evaporation-residue production is observed for the more symmetric combinations, ⁴⁸Ca+168,170Er. We relate this to the significant quasifission components already observed for these systems.