Electron-capture delayed fission properties of 228Np.

Electron-capture delayed fission of ${}^{242}\mathrm{Es}$ produced via the ${}^{233}\mathrm{U}{(}^{14}\mathrm{N}{,5n)}^{242}\mathrm{Es}$ reaction at 87 MeV (on target) was observed to decay with a half-life of $11\ifmmode\pm\else\textpm\fi{}3\mathrm{s},$ consistent with the reported \ensuremath{\alpha}-decay half-life of ${}^{242}\mathrm{Es}$ of ${16}_{\ensuremath{-}4}^{+6}\mathrm{s}.$ The mass-yield distribution of the fission fragments is highly asymmetric. The average pre-neutron emission total kinetic energy of the fragments was measured to be $183\ifmmode\pm\else\textpm\fi{}18\mathrm{MeV}.$ Based on the ratio of the measured number of fission events to the measured number of \ensuremath{\alpha} decays from the electron-capture daughter ${}^{242}\mathrm{Cf}$ (100% \ensuremath{\alpha} branch), the probability of delayed fission was determined to be $0.006\ifmmode\pm\else\textpm\fi{}0.002.$ This value for the delayed fission probability fits the experimental trend of increasing delayed fission probability with increasing Q value for electron capture.