Possible shears bands in 204At and 206Fr, and identification of excited states in 205,207Fr

Neutron-deficient astatine and francium nuclei were produced in the reaction Si-30+Ta-181 -> Fr-211(*) at 152 MeV. The evaporation residues from this very fissile system were selected with the HERCULES-II detector system and residue-gated gamma rays were measured with Gammasphere. Excited states were observed for the first time in Fr-205,Fr-207, as well as sequences of low-energy transitions between high-spin states in At-204 and Fr-206. These latter structures have properties similar to those associated with magnetic rotation (shears bands) in lead nuclei. Comparisons with established shears bands are presented and prospects for the magnetic-rotation phenomenon near the predicted N=120 magic number are explored.