Nuclear structure and selection rules in the rotational quasi-continuum

The γ-decay of excited rotating nuclei is studied as function of heat energy through a statistical analysis of the fluctuation of counts in γ-γ coincident spectra. In particular, making use of the covariance technique between spectra gated by different intrinsic configurations, one can find if there are similarities among cascades feeding into different selected bands. This can be used to learn about the transition between order to chaos in the nuclear many-body system, in terms of the validity of selection rules associated with the quantum numbers of the intrinsic structure. Experimental results on the nucleus 164Yb seem to indicate a possible weakening of the selection rules already at the moderate excitation energy ≥ 1 MeV above yrast, probed by the rotational decay-flow. (author)