Level structure of Th-227 investigated in the alpha decay of U-231

The level structure of 227Th has been studied using the α decay of 231U. The use of mass-separated 231U sources and high-resolution α-particle and γ-ray spectroscopy enabled the identification of 16 excited levels of 227Th. The angular distribution of α particles in the decay of low-temperature oriented 227Th is consistent with a 227Th ground-state spin of 1/2. The low-lying levels of 227Th can be interpreted in terms of a K=1/2± parity doublet and a K=3/2+ band coupled with the 1/2+ member of the parity doublet by the Coriolis interaction.