Observation of a fission mode with very short elongation for the neutron-rich 257Md nucleus at high excitation energy

Mass and total kinetic-energy (TKE) distributions of fission fragments from Md-257 nucleus populated by complete fusion of F-19 with U-238 have been measured in the range of excitation energy E* approximate to 37-48 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: F-19 + Th-232 and O-18 + U-238 involving first a different target and then a different projectile leading to compound nuclei Es-251 and Fm-256, respectively, at similar excitation energies and comparing their mass-TKE correlation plots. The existence of considerable supershort mode of fission for the Md-257 nucleus up to E* approximate to 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.

Automated summary

The mass and total kinetic-energy distributions of fission fragments from the Md-257 nucleus through the complete fusion of F-19 with U-238 have been measured in the range of excitation energy approximately 37-48 MeV. Experimental results show the existence of a significant supershort mode of fission for the Md-257 nucleus up to approximately 48 MeV, revealing deviations from liquid drop model predictions for neutron-rich exotic nuclei even at high excitation energies.