INDEPENDENT AND CUMULATIVE YIELDS OF VERY NEUTRON-RICH NUCLEI IN 20 MEV P-INDUCED AND 18-41 MEV D-INDUCED FISSION OF U-238

Independent and cumulative yields in nearly symmetric fission have been measured for the first time by bombarding U-238 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 +/- 0.20 (A = 110), 45.15 +/- 0.15 (A = 112), and 45.74 +/- 0.15 (A = 114). The widths (standard deviations) of the charge dispersion curves were 0.82 +/- 0.08 (A = 112) and 0.54 +/- 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 80Ge was determined to be 65%. Altogether some 15 new neutron-rich isotopes have been found, the newest one being 114Ru with a half-life of 0.53 +/- 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/mu-C, but for new isotopes independent yields as low as a few atoms/mu-C could be observed.