Covariance analysis of selection rules governing the gamma-decay cascades of the rotational nucleus Yb-164

The gamma-cascades feeding specific intrinsic configurations of Yb-164 are studied making use of a statistical analysis of counts fluctuations in gamm a-gamma coincident spectra. In particular, variance and covariance spectra are obtained starting from the measured (0, +), (0, -) and (1, -) gate-sele cted matrices. The analysis of the first ridge of the spectra yields about 25 excited bands carrying rotational energy correlations for the total spec trum, and about 10 in coincidence with each of the (alpha, pi) configuratio ns. The covariance of count fluctuations between the different (alpha, pi) gates is expressed by an experimental correlation coefficient, r, which mea sures the degree of sharing of decay paths through the excited bands, and t hereby the extent to which selection rules are obeyed by the decay. The cor relation coefficient is around r approximate to 0.3 for the ridge, and also in general rather small for valley fluctuations, Only at the highest valle y energies, a tendency to larger correlation coefficients is seen, indicati ng some weakening of the selection rules over longer decay cascades. The re sults of the experimental analysis are compared to rotational damping model predictions based on cranked shell model plus residual interactions, and r ather good agreement is found. (C) 2000 Published by Elsevier Science B.V. All rights reserved.