New transitions and levels in 148 Ce have been observed in a γ-γ-γ coincidence study from the spontaneous fission of 252 Cf with Gammasphere detector array. The ground band has been extended up to I π = 22 + , and side bands are extended with I = 2 stretched transitions and I = 1 crossing transitions. The observed level scheme is interpreted in terms of possible octupole correlations. Two sets of interwined positive-and negativeparity bands with the simplex quantum numbers s = ±1 are suggested. The results of B(E1)/B(E2) branching ratios indicate that the octupole correlations in 148 Ce are strong.

No abstract

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.

No abstract

Identification of Collective Oblate Bands in 138Ce * ZHU Sheng-jiang(%@,E)', LI Ming(%m)', ZHU Ling-yan(%&@B)', GAN C u i -y u n ( g S Z ) ' , M. Sakhaee(