We have studied the pre-yrast $\gamma$ decay of high-spin states in Yb isotopes excited highly above the yrast line in oxygen-induced $\mathrm{xn}$ reactions on Sm targets. We measured energy spectra, $\gamma$-ray multiplicities, angular correlations, and feeding times. The multiplicities increase with the $\gamma$ de-excitation energy. The $\gamma$-ray anisotropy indicates a dominant quadrupole character of the de-excitation $\gamma$ continuum. Hindered feeding times into the ground-band states were observed for ${}_{}{}^{158}{}_{}{}^{}\mathrm{Yb}$ but not for the decoupled states in ${}_{}{}^{159}{}_{}{}^{}\mathrm{Yb}$.

• Received 15 September 1975

DOI:https://doi.org/10.1103/PhysRevLett.35.1694