Direct Observation of Nonequilibrium Effects in Sequential Fission

Kinematically complete experiments have been performed on the three-body exit channels in 12.5-MeV/u ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ on ${}_{}{}^{122}{}_{}{}^{}\mathrm{Sn}$. The events observed result from a sequential fission process taking place in 1×${10}^{-21\mathrm{}}$ s. The angular distribution of the fission axis is approximately collinear with the axis of the first scission, and the mass distribution of the fission is asymmetric with the heavier mass preferentially emitted opposite to the direction of the third particle. These effects show the existence of a new phenomenon of nonequilibrium fission.