α decay studies of the nuclides U218 and U219

Very neutron deficient uranium isotopes were produced in fusion evaporation reactions using Ar40 ions on W182 targets. The gas-filled recoil separator RITU was employed to collect the fusion products and to separate them from the scattered beam and other reaction products. The activities were implanted into a position sensitive silicon detector after passing through a gas-counter system. The isotopes were identified using spatial and time correlations between the implants and the decays. Two α-decaying states, with Eα= (8612±9) keV and T1/2=(0.51-0.10+0.17) ms for the ground state and Eα=(10678±17) keV and T1/2=(0.56-0.14+0.26) ms for an isomeric state, were identified in U218. In addition, the half-life and α-decay energy of U219 were measured with improved precision. The measured decay properties deduced for U218 suggest that there is no subshell closure at Z=92. © 2007 The American Physical Society.