Is the K-quantum number conserved in the order-to-chaos transition region?

To study the order-to-chaos transition in nuclei we investigate the validity of the K-quantum number in the excited rapidly rotating 163Er nucleus, analyzing the variance and covariance of the spectrum fluctuations of γ-cascades feeding into low-K and high-K bands. The data are compared to simulated spectra obtained using a microscopic cranked shell model. K-selection rules are found to be obeyed for decay along excited unresolved rotational bands of internal excitation energy up to around 1.2 MeV and angular momenta 20ℏ⩽I⩽40ℏ. At higher internal energy, from about 1.2 to 2.5 MeV, the selection rules are found to be only partially valid.