Band Termination at Very High Spin inYb158

The unusual yrast spectrum of ${}_{}{}^{158}{}_{}{}^{}\mathrm{Yb}$ at very high spins is interpreted in terms of a band termination at $I^{\pi }={36}^{+}$. A similar spectrum with band terminations is obtained in microscopic cranking calculations for this nucleus. A basic element of the theory is that the finiteness of rotational bands is connected with a gradual shape change until the rotation takes place around a symmetry axis.