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

Abstract To study the order-to-chaos transition in nuclei we investigate the validity of the K -quantum number in the excited rapidly rotating 163 Er 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 20 ℏ ⩽ I ⩽ 40 ℏ . At higher internal energy, from about 1.2 to 2.5 MeV, the selection rules are found to be only partially valid.