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Register a new userMulti-phonon $gamma$-vibrational bands in odd-mass nuclei studied by triaxial projected shell model approach
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Inspired by the recent experimental data (Phys. Lett. B {bf 675} (2009) 420), we extend the triaxial projected shell model approach to study the $gamma$-band structure in odd-mass nuclei. As a first application of the new development, the $gamma$-vibrational structure of $^{103}$Nb is investigated. It is demonstrated that the model describes the ground-state band and multi-phonon $gamma$-vibrations quite satisfactorily, supporting the interpretation of the data as one of the few experimentally-known examples of simultaneous occurrence of one- and two-$gamma$-phonon vibrational bands. This generalizes the well-known concept of the surface $gamma$-oscillation in deformed nuclei built on the ground-state in even-even systems to $gamma$-bands based on quasiparticle configurations in odd-mass systems.
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We expand the triaxial projected shell model basis to include triaxially-deformed multi-quasiparticle states. This allows us to study the yrast and gamma-vibrational bands up to high spins for both gamma-soft and well-deformed nuclei. As the first application, a systematic study of the high-spin states in Er-isotopes is performed. The calculated yrast and gamma-bands are compared with the known experimental data, and it is shown that the agreement between theory and experiment is quite satisfactory. The calculation leads to predictions for bands based on one- and two-gamma phonon where current data are still sparse. It is observed that gamma-bands for neutron-deficient isotopes of 156Er and 158Er are close to the yrast band, and further these bands are predicted to be nearly degenerate for high-spin states.
Doublet bands observed in $^{124,126,130,132}$Cs isotopes are studied using the recently developed multi-quasiparticle microscopic triaxial projected shell model (TPSM) approach. It is shown that TPSM results for energies and transition probabilities are in good agreement with known energies and the recently measured extensive data on transition probabilities for the bands in $^{126}$Cs. In particular, it is demonstrated that characteristics transition probabilities expected for the doublet bands to originate from the chiral symmetry breaking are well reproduced in the present work. The calculated energies for $^{124,130,132}$Cs are also shown to be in reasonable agreement with the available experimental data. Furthermore, a complete set of the calculated transition probabilities is provided for the doublet bands in $^{124,130,132}$Cs isotopes.
Chiral rotation observed in $^{128}$Cs is studied using the newly developed microscopic triaxial projected shell model (TPSM) approach. The observed energy levels and the electromagnetic transition probabilities of the nearly degenerate chiral dipole bands in this isotope are well reproduced by the present model. This demonstrates the broad applicability of the TPSM approach, based on a schematic interaction and angular-momentum projection technique, to explain a variety of low- and high-spin phenomena in triaxial rotating nuclei.
Distribution of the two phonon $gamma$ vibrational collectivity in the rotating triaxial odd-$A$ nucleus, $^{103}$Nb, that is one of the three nuclides for which experimental data were reported recently, is calculated in the framework of the particle vibration coupling model based on the cranked shell model plus random phase approximation. This framework was previously utilized for analyses of the zero and one phonon bands in other mass region and is applied to the two phonon band for the first time. In the present calculation, three sequences of two phonon bands share collectivity almost equally at finite rotation whereas the $K=Omega+4$ state is the purest at zero rotation.
In this contribution, we present the cluster shell model which is analogous to the Nilsson model, but for cluster potentials. Special attention is paid to the consequences of the discrete symmetries of three alpha-particles in an equilateral triangle configuration. This configuration is characterized by a special structure of the rotational bands which can be used as a fingerprint of the underlying geometric configuration. The cluster shell model is applied to the nucleus 13C.
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