Abstract
A model of strongly coupled quadrupole and octupole vibrations and rotations is applied to de- scribe non-yrast alternating-parity sequences in even-even nuclei and split parity-doublet spectra in odd-mass nuclei. In even-even nuclei the yrast alternating-parity sequence includes the ground-state band and the lowest negative-parity levels with odd angular momenta, while the non-yrast sequences include excited β-bands and higher negative-parity levels. In odd-mass nuclei the yrast levels are described as low-energy rotation-vibration modes coupled to the ground single-particle (s.p.) state, while the non-yrast parity-doublets are obtained as higher-energy rotation-vibration modes coupled to excited s.p. configurations. We show that the extended model scheme describes the yrast and non-yrast quadrupole-octupole spectra in both even-even and odd-A nuclei. The involvement of the reflection-asymmetric deformed shell model to explain the single-particle motion and the Coriolis interaction in odd nuclei is discussed.
Highlights
The appearance of alternating-parity bands in even-even atomic nuclei, and quasi parity-doublet sequences in odd mass nuclei is known to be the result of the presence of quadrupole-octupole deformations [1]
We show that the extended model scheme describes the yrast and non-yrast quadrupole-octupole spectra in both even-even and odd-A nuclei
In addition to the yrast alternatingparity band composed by the members of the groundstate band and the lowest negative-parity levels the model scheme adopted couples of excited β-bands and higher negative-parity sequences with odd angular momenta
Summary
The appearance of alternating-parity bands in even-even atomic nuclei, and quasi parity-doublet sequences in odd mass nuclei is known to be the result of the presence of quadrupole-octupole deformations [1]. These spectra are attended by enhanced electric E1 and E3 transitions between levels with opposite parity. In addition to the yrast alternatingparity band composed by the members of the groundstate band and the lowest negative-parity levels the model scheme adopted couples of excited β-bands and higher negative-parity sequences with odd angular momenta. It will be shown that the common model mechanism of collective quadrupoleoctupole excitations can generate the non-yrast spectra in both even-even and odd-mass nuclei. In this work the coupling of the core to the odd nucleon and the Coriolis interaction in odd-mass nuclei are taken into account phenomenologically, while the model approach remains open for the involvement of a microscopic treatment of the single-particle degrees of freedom
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