Search for the Wobbling Mode in $^{171}$Ta

Perhaps the strongest evidence for a nucleus possessing {\it stable} triaxial deformation is the observation of a wobbling excitation. Such exotic sequences have been confirmed in $\pi i_{13/2}$ bands of $N\approx 94$ Lu nuclei [1], and the region may extend to $N\approx 100$ in Hf nuclei. However, it has not been possible to confirm the presence of wobbling structures in the heavier isotopes [2]. In order to determine whether stable triaxiality plays a role in $N\approx 100$ nuclei, an experiment was conducted to search for the wobbling mode in $^{171}$Ta. High-spin states in $^{171}$Ta were produced in the $^{124}$Sn($^{51}$V,$4n$) reaction and the $\gamma$ rays were detected with Gammasphere. Although the $i_{13/2}$ band was extended to (101/2), no wobbling structure was identified. The implications of this result on the region of triaxiality will be discussed. [1] S.W. Odegard {\it et al.}, Phys. Rev. Lett. {\bf 86}, 5866 (2001). [2] D.J. Hartley {\it et al.}, Phys. Lett. B {\bf 608}, 31 (2005).