Experimental study of the nuclear rotational motion with statistical analysis methods

The gamma-decay of excited rotating nuclei in the high level density region a few MeV above the yrast line has been studied through a statistical anal ysis of the fluctuation of counts in gamma-gamma coincident spectra. In par ticular, making use of the covariance technique between spectra gated by di fferent intrinsic configurations, one can measure how the cascades feeding into different selected bands are similar. The aim is to learn about the tr ansition between order to chaos in the nuclear many-body system, in terms o f the validity of selection rules associated with the quantum numbers of th e intrinsic structure. Experimental results on the nucleus Yb-164 are prese nted and compared to model predictions based on cranked shell model calcula tions including a two-body residual interaction.