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We present shell model calculations for warm rotating nuclei, combining the cranked Nilsson mean field and a residual surface-delta two-body interaction. The model is used to describe the transition from the region of well-defined rotational bands into the region dominated by rotational damping, and the results are in overall agreement with the experimental findings.

Several of the known rotational bands in 164Er are extended considerably (to around 35 h). In addition, a new coupled band is established and found to decay by an isomeric transition with t1/2 ≥ 170 nsec, to the 11t - state of the known Kπ =7− two-quasi-proton band. The new band is interpreted as a four-quasi-particle structure, with measured values of B(M1)/B(E2) consistent with the configuration [7t -] ⊗ ?i13/2[642 5/2+] ⊗ ?h9/2[523 5/2t -], i.e. [7t -]⊗ [AE,AF]. This is supported by the observation of a crossing which resembles the second i13/2 neutron crossing, BC, associated with the two-quasi-neutron band built on the configuration, [AE,AF]. The routhian of the new band is close to the sum of the individual routhians of [AE,AF] and [7−]. The cause of a small gain in energy of 130–272 keV is discussed.

Rotational motion loses its coherence as a function of the nuclear internal excitation energy. The damping process does not proceed in a continuous fashion and scars of discrete rotational bands are found, inbedded in a background of damped rotational states, regardless whether the calculations are carried out using effective or “random” forces. The complexity of the damping mechanism is revealed in the lineshape of the ridges in the γ-γ correlation spectrum.