Fragment mass distribution of the ${}^{239}\mathrm{Pu}\mathrm{}(d,pf)\mathrm{}$ reaction via the superdeformed β-vibrational resonance

We measured, for the first time, the mass distribution of ${}^{240}\mathrm{Pu}$ fission fragments following the β-vibrational resonance, whose level is formed on the second minimum of the double-humped fission barrier. The distribution shows an asymmetric mass distribution similar to the one observed for thermal neutron-induced fission of ${}^{239}\mathrm{Pu}$ and isomeric fission of ${}^{240}\mathrm{Pu}.$ This indicates that the ${}^{240}\mathrm{Pu}$ system following the β-vibrational resonance descends into a fission valley which is identical to the fission valley of the ${}^{240}\mathrm{Pu}$ isomer and ${}^{239}\mathrm{Pu}{(n}_{\mathrm{th}},f).\mathrm{}$