Observation of Rigid Nuclear Rotation

States in ${}_{}{}^{84}{}_{}{}^{}\mathrm{Zr}$ with angular momenta up to $34\hslash$ and rotational frequency 1.3 MeV have been studied with the techniques of discrete-line gamma-ray spectroscopy. The measurements probe the region beyond a second upbend. In this region the results are consistent with the nucleus having undergone a transition to an axially symmetric shape with $\beta =0.43\mathrm{}\pm 0.06$ and $\gamma =3\mathrm{}°\pm 6°$ which rotates with the rigidbody moment of inertia.