Possible Conservation of the K-Quantum Number in Excited Rotating Nuclei

The {gamma} cascades feeding into low-{ital K} and high-{ital K} bands in {sup 163}Er are investigated analyzing variances and covariance of the spectrum fluctuations. From a large data set of 10{sup 9} triple coincidences, {gamma}-{gamma} coincidence spectra gated by resolved low-lying rotational bands are analyzed. Low-{ital K} bands are found to be fed by a much larger effective number of cascades than high-{ital K} bands. The covariance between pairs of gated spectra shows that the cascades feeding low-{ital K} bands are different from those feeding the high-{ital K} bands. The persistence of the {ital K}-selection rules for the excited rotational bands within the angular momentum region 30{h_bar}{le}{ital I}{le}40{h_bar} is suggested as explanation. {copyright} {ital 1996 The American Physical Society.}