Excited states have been observed for the first time in the very neutron-deficient, odd-odd nucleus, ${}_{55}^{116}{\mathrm{Cs}}_{61}$. The assignment to ${}^{116}\mathrm{Cs}$ has been made by the detection of γ rays in coincidence with evaporated charged particles and with evaporation residues. The observed states form a rotational band which has been assigned to the $\nu (h_{11/2})\hspace{1em}\otimes \hspace{1em}\pi (h_{11/2})$ configuration. Tentative spin assignments have been made on the basis of systematic comparisons with neighboring cesium isotopes. A low-spin signature inversion is observed in the band at a rotational frequency of about 0.23 MeV$/\hslash$. The observed signature inversions in the odd-odd ${}^{116-126}\mathrm{Cs}$ isotopes have been compared with the results of extended total Routhian surface calculations, in which signature inversion arises as a consequence of quadrupole-pairing correlations and triaxial deformation. As previously shown for some of the odd-odd $A\simeq 120$ isotopes, the calculations reproduce the signature inversions reasonably well.

• Received 16 September 2005

DOI:https://doi.org/10.1103/PhysRevC.74.034310