Nuclear structure and selection rules in the rotational quasi-continuum

The gamma-decay of excited rotating nuclei is studied as function of heat e nergy through a statistical analysis of the fluctuation of counts in gamma- gamma coincident spectra. In particular, making use of the covariance techn ique between spectra gated by different intrinsic configurations, one can f ind if there are similarities among cascades feeding into different selecte d bands. This can be used to learn about the transition between order to ch aos in the nuclear many-body system, in terms of the validity of selection rules associated with the quantum numbers of the intrinsic structure. Exper imental results on the nucleus Yb-164 Seem to indicate a possible weakening of the selection rules already at the moderate excitation energy greater t han or equal to 1 MeV above yrast, probed by the rotational decay-flow.