Reflection Symmetry and Fission Mass Ratios

It is shown that the collective potential energy surfaces for rapid deformations leading to nuclear scission favor asymmetric mass division. A "walk-run" fission process is proposed, in which a slow deformation to the saddle-point shape is appropriately described by the liquid-drop model, and a rapid collective deformation then carriers the nucleus from saddle point to scission. The most probable mass ratio decreases with decreasing $\frac{{Z}^{2}}{A}$, in qualitative agreement with empirical fact.