Rotational band structures and lifetime measurements in¹³⁰Ce

The deformed nucleus 130Ce has been studied using the techniques of in-beam gamma -ray spectroscopy. Beams of 16O and 18O were used on targets of 116,117,118Sn to obtain excitation energies, mean lifetimes, spins, parities, mixing ratios and branching ratios. The gamma - gamma coincidence data necessary to determine the decay scheme were obtained using an array of five escape-suppressed spectrometers. The yrast band has been extended to Jpi =24+, or possibly Jpi =26+, with mean lifetimes measured for states up to Jpi =22+. Five new bands have been established and a 150 ns isomer has been identified at an excitation energy of 2454 keV. Backbending is observed due to the alignment of two h11/2 protons at the same rotational frequency in both the yrast band and the bands on the isomer. The gamma band based on the 834 keV (Jpi =2+) state can be identified with a triaxial shape corresponding to gamma approximately=-25 degrees . This band backbends at spin 10+ due to the alignment of two h11/2 protons showing softness of the nucleus and the coexistence of different shapes. The data may be interpreted in terms of the cranking model by assuming a prolate deformation with epsilon 2 approximately=0.25. The measured transition strengths in the yrast band generally show a decrease in epsilon 2 or a change in triaxiality from gamma approximately=0 degrees to gamma approximately=30 degrees . The transition rates measured for the 12+ to 10+ and 14+ to 12+ transitions are bigger than expected and are consistent with an increase in deformation to epsilon 2=0.30-0.35.

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