α-decays of neutron-deficient americium isotopes

Neutron-deficient americium isotopes ^{233,234,235,236}Am were produced in the bombardment of multiple thin targets of ²³³U and ²³⁵U with 7.6-10.5 MeV/nucleon ⁶Li ions. The reaction products were effectively mass-separated using the on-line isotope separator (JAERI-ISOL) coupled to a helium gas-jet transport system. For the first time, the α transition of ²³⁵Am was observed, and some improved α-decay data for ^233,234,236Am and²²⁹Np (α-decay daughter of ²³³Am) were accumulated. The α-particle energies of ²³³Am and ²³⁵Am were determined to be 6780±17 keV and 6457±14 keV and their half-lives were 3.2±0.8 min and 10.3±0.6 min, respectively. Measured α-decay branching ratios of ²³⁵Am and ²²⁹Np were (4.0±0.5) × 10^-3 and 0.68±0.11, respectively, while the lower limit for α-decay of ²³³Am was deduced to be 3 × 10^-2. Hindrance factors and probable assignments of the levels involved in those α transitions are discussed.