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.

中文翻译：

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高激发能下富中子Md257核裂变模式的观察

裂变碎片的质量和总动能 (TKE) 分布 ${}^{257}\mathrm{医学博士}$ 由完全融合形成的核 ${}^{19}\mathrm{F}$ 和 ${}^{238}\mathrm{你}$ 已在激发能量范围内测量 ${乙}^{*}\approx 37\text{-}48\mathrm{电动汽车}$. 由于测量的 TKE 分布的偏度，需要两个高斯分布来解释数据。具有高 TKE 的事件必须源自超短裂变模式，其存在已通过测量两个额外的反应得到证实：${}^{19}\mathrm{F}+{}^{232}钍$ 和 ${}^{18}\mathrm{哦}+{}^{238}\mathrm{你}$ 首先涉及不同的目标，然后涉及导致复合核的不同射弹 ${}^{251}\mathrm{埃斯}$ 和 ${}^{256}\mathrm{调频}$，分别在相似的激发能量下并比较它们的质量-TKE 相关图。存在相当多的超短裂变模式${}^{257}\mathrm{医学博士}$ 核高达 ${乙}^{*}\approx 48$ 首次观察到的 MeV 表明，即使在高激发能量下，这种富含中子的奇异核的罕见裂变模式与液滴模型预测相去甚远。