Observation of new levels and proposed octupole correlations in neutron-rich 150Ce

Background: The very neutron-rich Ce-150 is located at the edge of the Z = 56, N = 88 octupole deformed island. Studying its high spin states and octupole correlations is important for systematically understanding the nuclear structural characteristics in this region. Purpose: To investigate the high spin state levels and to search for octopole correlations in Ce-150. Methods: The high spin states of Ce-150 are studied by measuring the prompt gamma rays in the spontaneous fission of Cf-252. The data analysis uses the gamma-gamma-gamma coincidence methods. The gamma -> gamma(theta) angular correlation measurements are used to determine the spin and indirectly determine the parity of particular levels. Results: A new level scheme of Ce-150 is established. A total of 47 new transitions and 25 new levels are identified, compared with previous results. Six collective bands have been observed, and five of them are newly established. An octupole band structure with s = +1 in Ce-150 has been proposed. Systematic analysis of the B(E1)/B(E2) branching ratios, the levels of the octupole bands, the energy differences between negative- and positive-parity bands, and the moments of inertia of the bands is carried out for Ce-144,Ce-146,Ce-148,Ce-150. This analysis gives evidence for our assignment of octupole correlations in Ce-150. The other characteristics of the octupole bands are discussed. Conclusions: An octupole band structure is proposed in Ce-150. The octupole correlations in Ce-150 are weaker and show more instability than the neighboring lighter Ce isotopes.