Rotational band structures in ${}^{162,164}\mathrm{Dy}$ were studied by projectile inelastic excitation on a ${}^{118}\mathrm{Sn}$ target at near-barrier energies. States with spin up to ${24}^{+}{(22\mathrm{}}^{+})$ of the ground-state band and ${18}^{+}{(18\mathrm{}}^{+})$ of the $\gamma$-vibrational band in ${}^{162}\mathrm{Dy}{(}^{164}\mathrm{Dy})$ were populated in these reactions. States with spin spanning from $8^{+}$ to ${20}^{+}$ of the rotationally aligned S band in ${}^{162}\mathrm{Dy}$ were populated by way of its band-crossing point with the $\gamma$-vibrational band at spin ${12}^{+},$ where strong mixing occurred due to an accidental degeneracy. This S band eventually crosses the ground-state band at spin ${18}^{+}$ and becomes the yrast at spin ${20}^{+}.$ From the peripheral-collision $\gamma$-ray yield data, sets of electromagnetic matrix elements for both the intraband and interband transitions were determined by using the Coulomb excitation code, GOSIA. The measured intraband $E2\mathrm{}$ matrix elements were used to derive a quadrupole deformation of the S band that is $\approx 20\%$ larger than those of the nearby low-lying collective bands. This represents the first measurement made for the quadrupole deformation of the S band for states well below the crossing point with the ground-state band. The two-phonon $\gamma$-vibration harmonic strength in ${}^{162}\mathrm{Dy}$ is highly fragmented, 36% of the strength is located in two $K^{\pi }{=4\mathrm{}}^{+}$ bands at excitation energies 1535.9 and 2181.0 keV, respectively. Significant octupole collectivity was observed coupling the ground-state band to the $K^{\pi }{=2\mathrm{}}^{-}$ band in ${}^{162}\mathrm{Dy}.$

• Received 27 July 2001

DOI:https://doi.org/10.1103/PhysRevC.64.064317