The ${}^{122}\mathrm{Sn}({}^{11}\mathrm{B},4n)$ fusion-evaporation reaction at $E_{\mathrm{lab}}=60$ MeV was used to populate excited states in ${}^{129}\mathrm{Cs}$, and the deexcitations were investigated using in-beam $\gamma$-ray spectroscopic techniques. The level scheme of ${}^{129}\mathrm{Cs}$ is established up to ∼8 MeV excitation energy and 47/2 ħ spin. The observed band structures are interpreted for their configurations in the framework of cranking model calculations and systematic of the neighboring ${}_{55}$Cs isotopes. A negative-parity $\Delta I=1$ coupled band has been assigned the $\pi h_{11/2}\otimes \nu (h_{11/2}){}^2$ configuration as solution of the tilted-axis cranking, which coexists with the $\pi h_{11/2}$ yrast band resulting from the principal-axis cranking. A new band has been identified as a $\gamma$-vibrational band built on the $\pi h_{11/2}$ orbital. A pair of strongly coupled positive-parity bands exhibiting similar features have been assigned different unpaired three-quasiparticle configurations involving the $\pi h_{11/2}\otimes \nu h_{11/2}$ component. The previously identified unfavored signature partners of the $\pi d_{5/2}$ and $\pi g_{7/2}$ bands are reassigned as $\gamma$ vibrations of the core coupled to the $\pi g_{7/2}$ single-particle configuration, and the favored signature of the $\pi d_{5/2}$ band, respectively.

• Received 1 December 2008

DOI:https://doi.org/10.1103/PhysRevC.79.044317