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High spin level schemes of 118,119 Ag are established for the first time by analyzing the high statistics γ-γ-γ and γ-γ-γ-γ coincidence data from the spontaneous fission of

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Background : The very neutron-rich 150 Ce is located at the edge of the Z = 56, N=88 octupole deformed island. To study 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 150 Ce. Methods : The high spin states of 150 Ce are studied by measuring the prompt γ-rays in the spontaneous fission of 252 Cf. The data analysis is by using the γ-γ-γ coincidence methods. The γ → γ(θ) angular correlation measurements are used to determine the spin and indirectly parity of particular levels. Results : A new level scheme of 150 Ce is established. A total of 47 new transitions and 25 new levels are identified comparing with previous results. Six collective bands have been observed and five of them are newly established. An octupole band structure with s = +1 in 150 Ce has been proposed. Systematic analysis for 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 in 144,146,148,150 Ce. They give evidences for our assingment of octupole correlations in 150 Ce. The other characteristics of the octupole bands are discussed. Conclusions : An octupole band structure is proposed in 150 Ce. The octupole correlations in 150 Ce are weaker and show more instability than the neighboring lighter Ce isotopes.