The neutron-rich barium isotopes

The nuclei 142Ba, 144Ba and 146Ba (Z=56) have been studied using the technique of gamma-gamma angular correlations. The activities were produced using the on-line fission product mass separator OSTIS at the Institut Laue-Langevin. Spins have been assigned to most of the low-lying levels in these isotopes and multipole mixing ratios have been deduced. On the basis of coincidence data new information has been included in the decay schemes. The onset of nuclear deformation has been identified in these nuclei and found to occur between N=86 and N=88, which is two neutrons earlier than might be expected by comparison with the well known transitional nuclei in the Z=60 and 64 region. The current data are used to test the ability of the simplest form of the interacting boson model to describe this new transitional region.