Octupole correlations in neutron-rich La-145,La-147 nuclei: Coriolis-limit-coupling bands with aligned h(11/2) proton

Several new high-spin states are observed in the prompt gamma-rays emitted from the neutron-rich, odd-Z La-145,La-147 fragments produced in the sponta neous fission of Cf-252. Alternating parity bands are extended up to spins 41/2 and 43/2 in La-145,La-147, respectively. A new band completes the evid ence for two sell: of parity doublets expected for octupole correlations. E ight B(E1)/B(E2) ratios (four new) between two bands in La-145 are all esse ntially constant and somewhat larger than similar ratios in Ba-143,Ba-144, where stable octupole deformation and/or correlations are reported. The new ratios out of the 31/2(-) levels in both nuclei show a sharp spike compare d to other states, presumably from a strong reduction in E2 strengths in th is backbending region. In 145La, collective bands show competition and coex istence between symmetric and asymmetric shapes. Band crossings occur in bo th nuclei around (h) over bar omega approximate to 0.26-0.30 MeV. Their bac kbends are associated with the alignment of two i(13/2) neutrons according to cranked shell model calculations. [S0556-2813(99)08402-2].