Inelastic excitation of ${}^{170}\mathrm{Er}$ by a ${}^{238}\mathrm{U}$ beam, studied at near-barrier energies, has led to the observation of unusual features in rotational bands built on low-lying vibrations. The population of the high-spin members of the $K^{\pi }{=0\mathrm{}}^{+},$ $\beta$-vibrational band is enhanced due to mixing with the $K^{\pi }{=2\mathrm{}}^{+},$ $\gamma$-vibrational band at spin $4^{+}.$ Strong mixing of the $K^{\pi }{=0\mathrm{}}^{+}$ band with a rotationally aligned 2 qp band results in this band losing its $\beta$-vibrational character and in a rapid gain in spin alignment leading to a crossing with the ground-state band between spins ${20}^{+}$ and ${22}^{+}.$ The low-lying $K^{\pi }{=3\mathrm{}}^{+}$ band also is populated. It subsequently decays to both the $\gamma$-vibrational and the ground-state bands. The occurrence of appreciable K-forbidden $E2\mathrm{}$ transitions from the $K^{\pi }{=3\mathrm{}}^{+}$ to the ground-state band is attributed to mixing with the $K^{\pi }{=2\mathrm{}}^{+}$ band, caused by the interaction between the quadrupole $\gamma$-vibrational and the hexadecapole vibrational motions.

• Received 27 September 1999

DOI:https://doi.org/10.1103/PhysRevC.61.021305