High spin spectroscopy of 123 Ba and alignment processes for A ∼ 120

The level scheme of123Ba has been extended. Bands based on the [523]7/2− and [402]5/2+ Nilsson configurations were established to spins 59/2 (67/2 tentatively) and 29/2, respectively. The first backbend in this region is found to be caused by the alignment of a pair of h11/2 protons. For the first time in this mass region there is evidence for a second crossing due to the alignment of an h11/2 neutron pair in a neutron h11/2 band. The experimental results are compared with self-consistent cranking calculations. A previous suggestion that large γ-deformation is needed to explain the observed bandheads is not supported.