Observation of cold scission of highly excited fissioning nuclei

The time scale of fission at initial nuclear temperatures of about 5 MeV is deduced from the number of neutrons evaporated prior to and after scission in the reactions ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ and ${}_{}{}^{154}{}_{}{}^{}+(838\mathrm{}$ MeV) ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$. The prescission lifetime for fission with symmetric mass splits is longer than for asymmetric mass splits. For symmetric mass splits the excitation energy at scission is only about 60 MeV and independent of the initial excitation energy which is consistent with a prescission lifetime in the order of ${10}^{\mathrm{-}20}$ s.