Three-dimensional potential energy surface for fission of ${}^{236}$U within covariant density functional theory

We have calculated the three-dimensional potential energy surface (PES) for the fission of compound nucleus ${}^{236}$U using the covariant density functional theory with constraints on the axial quadrupole and octupole deformations $({\beta }_2,{\beta }_3)$ as well as the nucleon number in the neck $q_N$. By considering the additonal degree of freedom $q_N$, coexistence of the elongated and compact fission modes is predicted for $0.9\lesssim {\beta }_3\lesssim 1.3$. Remarkably, the PES becomes very shallow across a large range of quadrupole and octupole deformations for small $q_N$, and consequently, the scission line in $({\beta }_2,{\beta }_3)$ plane will extend to a shallow band, which leads to a fluctuation for the estimated total kinetic energies by several to ten MeV and for the fragment masses by several to about ten nucleons.