Abstract
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.
Highlights
The conditions under which K, the projection of aligned nucleonic angular momentum on the symmetry axis in deformed nuclei, is a good quantum number remain a topic of much current interest, as testified by the extensive experimental work on high-K isomers [1]
The study of nuclear states with high values of the K-quantum number is interesting from the point of view of the decay-out from such states and in connection with their feeding, which allows to investigate the validity of the associated selection rules at higher internal excitation energies
As it was stated by Mottelson [2], the question of K-quantum number violation in excited states is a key issue in the study of the transition between ordered and chaotic motion in nuclei caused by the residual interaction and the high level density
Summary
The conditions under which K, the projection of aligned nucleonic angular momentum on the symmetry axis in deformed nuclei, is a good quantum number remain a topic of much current interest, as testified by the extensive experimental work on high-K isomers [1]. The number of paths obtained from the analysis of the first ridge of the 2D matrices gated by individual bands is found, in average, to be ≈ 10 for each of the four low-K and of the three high-K configurations.
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