Collective oblate structure in the odd-odd isotopes128,130La

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Abstract
Excited states in the nuclei 128,130La have been investigated to high spin using gamma -ray spectroscopy techniques. In addition to the main rotational structures based on a prolate collective rotor, and a superdeformed band in 130La, two bands are seen with properties similar to the collective oblate structure proposed for 131La. The experimental evidence for these bands is discussed in terms of the variation in energy-level signature splitting, B(M1)/B(E2) ratios and mixing ratios as a function of rotational frequency and single-particle configuration. These results are interpreted using odd-odd particle-rotor model calculations and self-consistent cranking calculations. They are compared with the proposed 'collective oblate' bands in other nuclei in the A=130 region and possible evidence for collective oblate shape co-existence is presented.