Conclusive evidence of quasifission in reactions forming the 210 Rn compound nucleus

Fission fragment mass ratio distributions have been measured for the reactions {sup 16}O+{sup 194}Pt and {sup 24}Mg+{sup 186}W, both leading to the same compound nucleus, {sup 210}Rn, at near-barrier energies. The measured fission fragment mass ratio variances for {sup 16}O+{sup 194}Pt and {sup 24}Mg+{sup 186}W are compared with the calculations assuming compound nucleus formation. Mass variances of fragments from the {sup 24}Mg+{sup 186}W reaction show a dramatic deviation from the compound nucleus behavior. This suggests strong evidence for onset of the quasifission process in this reaction.