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Theoretical Description of K-Isomers  [PDF]
Yang Sun
Physics , 2005, DOI: 10.1063/1.2187831
Abstract: A proper treatment of K-mixing is the key to understanding K-isomers. Here, we present a method based on the projected shell model. This method differs from the usual description of multi-quasiparticle states by introducing a transformation to the laboratory frame and a subsequent configuration mixing in that frame. It allows a quantitative study on the degree of K-violation through direct calculations of electromagnetic transitions.
Nature of $γ$-deformation in Ge and Se nuclei and the triaxial projected shell model description  [PDF]
G. H. Bhat,W. A. Dar,J. A. Sheikh,Y. Sun
Physics , 2014, DOI: 10.1103/PhysRevC.89.014328
Abstract: Recent experimental data have demonstrated that $^{76}$Ge may be a rare example of a nucleus exhibiting rigid $\gamma$-deformation in the low-spin regime. In the present work, the experimental analysis is supported by microscopic calculations using the multi-quasiparticle triaxial projected shell model (TPSM) approach. It is shown that to best describe the data of both yrast and $\gamma$-vibrational bands in $^{76}$Ge, a rigid-triaxial deformation parameter $\gamma\approx 30^\circ$ is required. TPSM calculations are discussed in conjunction with the experimental observations and also with the published results from the spherical shell model. The occurrence of a $\gamma\gamma$-band in $^{76}$Ge is predicted with the bandhead at an excitation energy of $ \sim$ 2.5 MeV. We have also performed TPSM study for the neighboring Ge- and Se-isotopes and the distinct $\gamma$-soft feature in these nuclei is shown to result from configuration mixing of the ground-state with multi-quasiparticle states.
Systematics of g factors of 2_1^+ states in even-even nuclei from Gd to Pt: A microscopic description by the projected shell model  [PDF]
Bao-An Bian,Yao-Min Di,Gui-Lu Long,Yang Sun,Jing-ye Zhang,Javid A. Sheikh
Physics , 2005, DOI: 10.1103/PhysRevC.75.014312
Abstract: The systematics of g factor of first excited 2^+ state vs neutron number N is studied by the projected shell model. The study covers the even-even nuclei of all isotopic chains from Gd to Pt. g factors are calculated by using the many-body wavefunctions that reproduces well the energy levels and B(E2)'s of the ground-state bands. For Gd to W isotopes the characteristic feature of the g factor data along an isotopic chain is described by the present model. Deficiency of the model in the g factor description for the heavier Os and Pt isotopes is discussed.
Gamow Shell Model Description of Weakly Bound Nuclei and Unbound Nuclear States  [PDF]
N. Michel,W. Nazarewicz,M. Ploszajczak,J. Okolowicz
Physics , 2003, DOI: 10.1103/PhysRevC.67.054311
Abstract: We present the study of weakly bound, neutron-rich nuclei using the nuclear shell model employing the complex Berggren ensemble representing the bound single-particle states, unbound Gamow states, and the non-resonant continuum. In the proposed Gamow Shell Model, the Hamiltonian consists of a one-body finite depth (Woods-Saxon) potential and a residual two-body interaction. We discuss the basic ingredients of the Gamow Shell Model. The formalism is illustrated by calculations involving {\it several} valence neutrons outside the double-magic core: $^{6-10}$He and $^{18-22}$O.
Isospin-projected nuclear level densities by the shell model Monte Carlo method  [PDF]
H. Nakada,Y. Alhassid
Physics , 2008, DOI: 10.1103/PhysRevC.78.051304
Abstract: We have developed an efficient isospin projection method in the shell model Monte Carlo approach for isospin-conserving Hamiltonians. For isoscalar observables this projection method has the advantage of being exact sample by sample. The isospin projection method allows us to take into account the proper isospin dependence of the nuclear interaction, thus avoiding a sign problem that such an interaction introduces in unprojected calculations. We apply our method in the calculation of the isospin dependence of level densities in the complete $pf+g_{9/2}$ shell. We find that isospin-dependent corrections to the total level density are particularly important for $N \sim Z$ nuclei.
Nuclear isomers: structures and applications  [PDF]
Yang Sun,Michael Wiescher,Ani Aprahamian,Jacob L. Fisker
Physics , 2005, DOI: 10.1063/1.2187858
Abstract: Isomeric states in the nuclei along the rapid proton capture process path are studied by the projected shell model. Emphasis is given to two waiting point nuclei Se-68 and Kr-72 that are characterized by shape coexistence. Energy surface calculations indicate that the ground state of these nuclei corresponds to an oblate-deformed minimum, while the lowest state at the prolate-deformed minimum can be considered as a shape isomer. Due to occupation of the orbitals with large K-components, states built upon two-quasiparticle excitations at the oblate-deformed minimum may form high $K$-isomers. The impact of the isomer states on isotopic abundance in X-ray bursts is studied in a multi-mass-zone X-ray burst model by assuming an upper-lower limit approach.
Triaxial projected shell model approach  [PDF]
J. A. Sheikh,K. Hara
Physics , 1998, DOI: 10.1103/PhysRevLett.82.3968
Abstract: The projected shell model analysis is carried out using the triaxial Nilsson+BCS basis. It is demonstrated that, for an accurate description of the moments of inertia in the transitional region, it is necessary to take the triaxiality into account and perform the three-dimensional angular-momentum projection from the triaxial Nilsson+BCS intrinsic wavefunction.
Gamow Shell-Model Description of Weakly Bound and Unbound Nuclear States  [PDF]
N. Michel,W. Nazarewicz,M. Ploszajczak,J. Rotureau
Physics , 2004, DOI: 10.1140/epjad/i2005-06-136-7
Abstract: Recently, the shell model in the complex k-plane (the so-called Gamow Shell Model) has been formulated using a complex Berggren ensemble representing bound single-particle states, single-particle resonances, and non-resonant continuum states. In this framework, we shall discuss binding energies and energy spectra of neutron-rich helium and lithium isotopes. The single-particle basis used is that of the Hartree-Fock potential generated self-consistently by the finite-range residual interaction.
Backbending in Dy isotopes within the Projected Shell Model  [PDF]
V. Velazquez,J. G. Hirsch,Y. Sun,M. W. Guidry
Physics , 1999, DOI: 10.1016/S0375-9474(99)00238-9
Abstract: A systematic study of the yrast band in 154-164 Dy isotopes using the Projected Shell Model is presented. It is shown that, in the context of the present model, enlarging the mean field deformation by about 20 % allows a very good description of the spectrum of yrast band in these isotopes. The dependence of the B(E2) values on angular momentum is also better described when larger deformations are used. The observed oscillation of g-factors at low spin states remains an open question for this model.
Enrichment of nuclear spin isomers by molecular coherent control  [PDF]
Pavel Chapovsky
Physics , 2001,
Abstract: Enrichment of nuclear spin isomers of molecules by infrared radiation resonant to molecular rovibrational transition is considered. Special attention is given to the enrichment by light-induced crossing of far separated ortho and para states.
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