Projected shell model study for the yrast-band structure of the proton-rich mass-80 nuclei

doi:10.1016/S0375-9474(00)00509-1

Nuclear Physics A

Volume 686, Issues 1–4, 9 April 2001, Pages 141-162

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Abstract

A systematic study of the yrast-band structure for the proton-rich, even–even mass-80 nuclei is carried out using the projected shell model approach. We describe the energy spectra, transition quadrupole moments and gyromagnetic factors. The observed variations in energy spectra and transition quadrupole moments in this mass region are discussed in terms of the configuration mixing of the projected deformed Nilsson states as a function of shell filling.

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A positive parity sequence of $Δ I = 2$ γ transitions has been identified above $I^{π} = 9 / 2^{+}$ state ( $E_{x} = 2019$ keV) in ¹¹⁵Sb through in-beam γ ray spectroscopic technique. Rotational features of this sequence are found similar to a low-K decoupled band. Observation of this newly identified low-K decoupled band, along with the earlier reported strongly coupled high-K band in this nucleus, provides the first experimental evidence for prolate-oblate shape coexistence associated with $g_{9 / 2}$ proton-hole configuration around $Z = 50$ shell closure. Experimental results are reproduced reasonably well in the frameworks of the projected shell model and the total Routhian surface calculations.
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The yrast lines in Kr isotopes with $N = 42$ , 44, and 46 are investigated in a beyond mean field framework with both prolate-oblate coexistence and quasiparticle alignment taken into account. Quasiparticle orbitals with high-j and low-Ω on the oblate side are shown to be responsible for the sharp backbending observed in ⁸²Kr, by driving the yrast shape from prolate to oblate. This suggests that quasiparticle alignment may not be neglected in the investigation of the shape evolution along the yrast line.
Systematical study of high-spin rotational bands in neutron-deficient Kr isotopes by the extended projected shell model
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Citation Excerpt :
With these deformation parameters and using the standard Nilsson parameters provided by Bengtsson and Ragnarsson [34], deformed single-particle states are generated. The early PSM calculations for this mass region but with smaller qp spaces made similar assumptions [35,42–45]. The (angular-momentum-projected) multi-qp configurations in PSM form a shell-model basis in which a two-body Hamiltonian is diagonalized.
We analyze the high-spin structure of the even–even ^72–80Kr isotopes using the Projected Shell Model (PSM). With the help of the Pfaffian formulas, we have vigorously extended the quasi-particle (qp) basis of the PSM code and applied in this mass region for the first time. We consider a sufficiently large multi-qp configuration space in order to describe high-spin rotational behavior. The results show that the calculation can reproduce most of the known rotational bands with positive- or negative-parity. Moreover, some side bands appearing in the near-yrast region are predicted. The main structure for each band is discussed in terms of multi-qp configurations. The variations in moment of inertia with spin are explained in terms of successive band crossings among the 2-qp, 4-qp, 6-qp, and 8-qp states. The $B (E 2)$ transition probabilities in these bands are also calculated. To further understand the high-spin behavior of these neutron-deficient nuclei and to confirm predictions of the present work, good high-spin data, especially for $B (E 2)$ transitions, are called for.
Study of nuclear structure of odd mass 119-127I nuclei in a phenomenological approach
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By using the phenomenological approach of Projected Shell Model (PSM), the positive and negative-parity band structures of odd mass neutron-rich ^119–127I nuclei have been studied with the deformed single-particle states generated by the standard Nilsson potential. For these isotopes, the band structures have been analyzed in terms of quasi-particles configurations. The phenomenon of backbending in moment of inertia is also studied in the present work. Besides this, the reduced transition probabilities, i.e. $B (E 2)$ and $B (M 1)$ , are obtained from the PSM wavefunction for the first time for yrast bands of these isotopes.
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The role of neutron–proton pairing correlations on the structure of nuclei along the $N = Z$ line is reviewed. Particular emphasis is placed on the competition between isovector ( $T = 1$ ) and isoscalar $(T = 0)$ pair fields. The expected properties of these systems, in terms of pairing collective motion, are assessed by different theoretical frameworks including schematic models, realistic Shell Model and mean field approaches. The results are contrasted with experimental data with the goal of establishing clear signals for the existence of neutron–proton ( $n p$ ) condensates. We will show that there is clear evidence for an isovector $n p$ condensate as expected from isospin invariance. However, and contrary to early expectations, a condensate of deuteron-like pairs appears quite elusive and pairing collectivity in the $T = 0$ channel may only show in the form of a phonon. Arguments are presented for the use of direct reactions, adding or removing an $n p$ pair, as the most promising tool to provide a definite answer to this intriguing question.
Investigation of doublet-bands in 124,126,130,132Cs odd-odd nuclei using triaxial projected shell model approach
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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 ¹²⁶Cs. 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 ^124,130,132Cs 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 ^124,130,132Cs isotopes.

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Nuclear Physics A

Abstract

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Cited by (53)

Coexistence of low-K oblate and high-K prolate g<inf>9/2</inf> proton-hole bands in <sup>115</sup>Sb

Prolate-to-oblate transition and backbending along the yrast line induced by quasiparticle alignment

Systematical study of high-spin rotational bands in neutron-deficient Kr isotopes by the extended projected shell model

Study of nuclear structure of odd mass <sup>119-127</sup>I nuclei in a phenomenological approach

Overview of neutron-proton pairing

Investigation of doublet-bands in <sup>124,126,130,132</sup>Cs odd-odd nuclei using triaxial projected shell model approach