Independent and cumulative yields of very neutron-rich nuclei in 20 MeV p- and 18-41 MeV d-induced fission of 238U.

Abstract

Independent and cumulative yields in nearly symmetric fission have been measured for the first time by bombarding $^{238}\mathrm{U}$ with 20-MeV protons and with 18-, 25-, and 41-MeV deuterons. Isobaric charge dispersion has been determined in the A=110, A=112, and A=114 mass chains and, from asymmetric fission, in the A=80 mass chain. The average isobaric charges in the p+U reaction were 44.01\ifmmode\pm\else\textpm\fi{}0.20 (A=110), 45.15\ifmmode\pm\else\textpm\fi{}0.15 (A=112), and 45.74\ifmmode\pm\else\textpm\fi{}0.15 (A=114). The widths (standard deviations) of the charge dispersion curves were 0.82\ifmmode\pm\else\textpm\fi{}0.08 (A=112) and 0.54\ifmmode\pm\else\textpm\fi{}0.08 (A=114). The average charges are roughly 0.3 unit higher than those calculated on the basis of the unchanged charge distribution model. The ground-state branch in the beta decay of $^{80}\mathrm{Ge}$ was determined to be 65%. Altogether some 15 new neutron-rich isotopes have been found, the newest one being $^{114}\mathrm{Ru}$ with a half-life of 0.53\ifmmode\pm\else\textpm\fi{}0.06 s. An ion guide facility was used to separate the isobaric chains on-line from other fission products. Typical cumulative yields in a mass chain were on the order of 1000 atoms/\ensuremath{\mu}C, but for new isotopes independent yields as low as a few atoms/\ensuremath{\mu}C could be observed.