Evidence for Nuclear Superfluidity in U236 Isomeric- and Prompt-Fission Modes

Isomer fission in $^{236m}\mathrm{U}$, ${t}_{\frac{1}{2}}=125$ nsec, from $^{235}\mathrm{U}(d, pf)$ was compared with prompt fission $^{235}\mathrm{U}({n}_{\mathrm{th}}, f)$, in twin experiments. Fine structure in the total kinetic energy, average total kinetic energy as a function of mass, and mass yield were observed in isomer fission of $^{236m}\mathrm{U}$. This observation is compatible with a superfluid descent from saddle to scission points. Two peaks in the total-kinetic-energy distribution from isomer fission are observed near fragment mass 132, and this is interpreted as due to the proton-pairing effect at $Z=50$.