Mass and total kinetic-energy (TKE) distributions of fission fragments from ${}^{257}\mathrm{Md}$ nucleus populated by complete fusion of ${}^{19}\mathrm{F}$ with ${}^{238}\mathrm{U}$ have been measured in the range of excitation energy $E^{*}\approx 37\text{−}48\mathrm{MeV}$. Due to the skewness of the measured TKE distributions, two Gaussian distributions were required to explain the data. The events with high TKE must originate from the supershort mode of fission, the presence of which has been confirmed by measuring two additional reactions: ${}^{19}\mathrm{F}+{}^{232}\mathrm{Th}$ and ${}^{18}\mathrm{O}+{}^{238}\mathrm{U}$ involving first a different target and then a different projectile leading to compound nuclei ${}^{251}\mathrm{Es}$ and ${}^{256}\mathrm{Fm}$, respectively, at similar excitation energies and comparing their mass-TKE correlation plots. The existence of considerable supershort mode of fission for the ${}^{257}\mathrm{Md}$ nucleus up to $E^{*}\approx 48$ MeV, observed for the first time, reveals that such rare fission modes for neutron-rich exotic nuclei are far off from the liquid drop model predictions, even at high excitation energies.

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• Fission
• Low & intermediate energy heavy-ion reactions
• Nuclear reactions
• A ≥ 220