Excited states in ${}^{128}$Xe have been populated in the fusion reaction ${}^{125}\mathrm{Te}(\alpha {,n)}^{128}\mathrm{Xe}$ with the aim of searching for mixed symmetry states at energies around 2 MeV. The $2_4^{+}$ state at 2.127 MeV decays to the 2${}_1^{+}$ state with a transition of 99.4% $M1\mathrm{}$ character. The lifetime of this state was measured by the Doppler attenuation technique. The $B\left(M1\mathrm{}\right)\mathrm{}$ value of the γ transition indicates the mixed symmetry character of the 2${}_4^{+}$ state. The experimental results are in good agreement with interacting boson model ($IBM-2\mathrm{}$) calculations. The decay selection rules of the 2${}^{+}$ mixed-symmetry states are discussed on the basis of the $\tau$ quantum numbers and the $d$ parity.

• Received 13 June 1997

DOI:https://doi.org/10.1103/PhysRevC.56.R2354