Backbending and Decoupled Bands inBa126,128

Abstract

We have observed in ${}_{}{}^{126}{}_{}{}^{}\mathrm{Ba}$ a $K=0^{+}$ rotational band, extending to $I={18}^{+}$, exhibiting strong backbending above the ${10}^{+}$ state, and probably branching up to a second ${12}^{+}$ state. Another band with spins $7^{-}$, $9^{-}$, ${11}^{-}$, ${13}^{-}$, and ${15}^{-}$ was also seen. A similar negative-parity band was observed in ${}_{}{}^{128}{}_{}{}^{}\mathrm{Ba}$. Coriolis calculations reproduce the negative-parity bands in ${}_{}{}^{126,128}{}_{}{}^{}\mathrm{Ba}$ and other nuclei suggesting that they are decoupled two-quasiparticle (qp) states. The crossing of a similar decoupled positive-parity 2-qp band and the 0-qp band can explain the backbending and the two ${12}^{+}$ states.