Strong evidence for quasifission in asymmetric reactions forming Po202

Fission fragment mass-angle correlations and mass ratio distributions have been measured for the reactions O16+Os186, Mg24+Hf178, S34+Er168, and Ti48+Sm154, forming the Po202 composite nucleus, at near barrier energies. Systematic analysis based on the expected dependence of the variance of the mass distribution on the angular momentum and temperature of the compound nucleus indicate that the two lighter systems evolve through true compound nucleus fission. Evidence of quasifission was observed for the two most mass-symmetric reactions, through strong mass-angle correlations for the Ti48+Sm154 reaction and a broadened mass ratio distribution for the S34+Er168 reaction. Furthermore, the increase in mass width at near barrier energies shows the influence of the alignment of statically deformed target nuclei.