Configuration changes and hindered decays in four- and six-quasiparticle isomers inTa178

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Abstract
A six-quasiparticle isomer with Kπ=21−, a half-life of 290(12) ms, and the π3ν3 configuration has been identified in the odd-odd nucleus Ta178, at an excitation energy of 2902 keV. The rotational bands built on the known Kπ=15− isomer and on the newly found 16+ four-quasiparticle and 22+ six-quasiparticle states, have also been identified, allowing characterization of the configurations. The 15− band is predominantly of πν3 character with a π3ν admixture. When the mixing is taken into account the excitation energies of the main yrast multi-quasiparticle states can be reproduced. The multi-quasiparticle states observed are related essentially through the addition of the two-quasiparticle component ν2[6+] or π2[6+]. Depending on whether the transition between the states involves the change ν2[6+]→[0] or π2[6+]→[0], the E2 hindrance factors for decays between the six- and four-quasiparticle states are relatively large or small. This dependence mimics the pattern observed in the two-quasiparticle core transitions and, because the 15− isomer is mainly πν3, the magnitude sequence is inverted compared to that observed in Ta176.

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