High-spin states in ${}^{164}\mathrm{Lu}$ were populated in the ${}^{121}\mathrm{Sb}$(${}^{48}\mathrm{Ca}$,$5n$) reaction at 215 MeV and γ-ray coincidences were measured with the Gammasphere spectrometer. Through this experiment the eight known triaxial superdeformed bands in ${}^{164}\mathrm{Lu}$ could be confirmed. Some of these bands were extended to higher as well as to lower spins. Evidence is reported for the first time for weak $\Delta I=1,E1$ transitions linking TSD3 and TSD1. This observation may imply coupling to octupole vibrational degrees of freedom. The decay mechanism is different from the one observed in the neighboring even-$N$ isotopes, which exhibit wobbling excitations built on the $\pi i_{13/2}$ structure with $E2(M1),\Delta I=1$ interband decay. An additional sequence decaying at high spin into TSD1 was observed up to $I^{\pi }=({50}^{-})$. This band has a constant dynamic moment of inertia of ∼$70\hslash {}^2{\mathrm{MeV}}^{-1}$ and an alignment that is $\text{∼}2\hslash$ larger than that found for TSD1. A revision of the assumed spin-parity-assignment of TSD2 is based on the observed decay-out to normal-deformed structures. The parity and signature quantum numbers of TSD2 are now firmly assigned as $(\pi ,\alpha )=(+,0)$, in disagreement with the former assignment of $(\pi ,\alpha )=(-,1)$, which was based on the assumption that TSD2 is the signature partner of TSD1. TSD1 and TSD2 show an alignment gain at $\hslash \omega \text{∼}0.67$ and 0.60 MeV, respectively. In TSD1 the involvement of the $j_{15/2}$ neutron orbital is suggested to be responsible for the high-frequency crossing.

• Received 6 December 2006

DOI:https://doi.org/10.1103/PhysRevC.75.044306