Rotational States inTm169

The decay of ${\mathrm{Yb}}^{169}$ has been investigated by means of a coincidence scintillation spectrometer. Eleven gamma rays have been arranged in a level scheme with levels at 10, 120, 142, 318, 336, 382, and 476 kev. The multipolarity of the strongest gamma rays has been determined and spin values assigned to some of the levels. It is found that five of the levels form a rotational band with $K=\frac{1}{2}$. In this case the Bohr-Mottelson unified model predicts an anomalous rotational spectrum. The experimental spectrum agrees very well with the theory. The gamma-ray intensities are discussed and there is a good agreement with the unified model also in this respect.