Direct Observation of Proximity Effects in Ternary Heavy-Ion Reactions

Kinematically complete experiments have been performed on the two- and three-body exit channels in 12.4-MeV/u ${}_{}{}^{84}{}_{}{}^{}\mathrm{Kr}$ on ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ and ${}_{}{}^{166}{}_{}{}^{}\mathrm{Er}$, and 12.5-MeV/u ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ on ${}_{}{}^{122}{}_{}{}^{}\mathrm{Sn}$. Three-body events occur with a high probability. They arise predominantly from two-step reactions, with large energy losses in the first step leading to fission in the second. Strong proximity effects, observed in the final three-body state of the Xe-Sn reaction, establish a scission-to-scission time of about 1×10${}_{}{}^{-21\mathrm{}}{}_{}{}^{}\mathrm{s}$.