43 research outputs found
Cranked shell model and isospin symmetry near N=Z
A cranked shell model approach for the description of rotational bands in
nuclei is formulated. The isovector neutron-proton pairing is
taken into account explicitly. The concept of spontaneous breaking and
subsequent restoration of the isospin symmetry turns out to be crucial. The
general rules to construct the near yrast-spectra for rotating nuclei are
presented. For the model case of particles in a j-shell, it is shown that
excitation spectra and the alignment processes are well described as compared
to the exact shell model calculation. Realistic cranked shell model
calculations are able to describe the experimental spectra of Kr and
Rb isotopes. \Comment: 23 pages, 5 figure
Symmetry-Projected Hartree-Fock-Bogoliubov Equations
Symmetry-projected Hartree-Fock-Bogoliubov (HFB) equations are derived using
the variational ansatz for the generalized one-body density-matrix in the
Valatin form. It is shown that the projected-energy functional can be
completely expressed in terms of the HFB density-matrix and the pairing-tensor.
The variation of this projected-energy is shown to result in HFB equations with
modified expressions for the pairing-potential and the Hartree-Fock field. The
expressions for these quantities are explicitly derived for the case of
particle number-projection. The numerical applicability of this projection
method is studied in an exactly soluble model of a deformed single-j shell.Comment: 24 pages, 1 figur
Nuclear magnetic dipole properties and the triaxial deformation
Nuclear magnetic dipole properties of ground bands and gamma-vibrational
bands are studied for the first time using the triaxial projected shell model
approach. The study is carried out for the Dy and Er isotopic chains, ranging
from transitional to well-deformed region. It is found that the g-factor ratio
of the 2^+ state in ground bands to that of gamma-bands, r=g(2^+,
gamma-vib)/g(2^+, ground), varies along an isotopic chain. With the
gamma-deformations, which best reproduce the energy levels for both bands, we
obtain a qualitative agreement with the experimental data. This result thus
suggests that study of the ratio may provide an important information on the
triaxial deformation of a nuclear system. The angular-momentum dependence of
the ground band g-factor on the triaxial deformation is also investigated.Comment: 9 pages, 4 figures, 1 table, final version accepted by Phys. lett.
Isovector and isoscalar superfluid phases in rotating nuclei
The subtle interplay between the two nuclear superfluids, isovector T=1 and
isoscalar T=0 phases, are investigated in an exactly soluble model. It is shown
that T=1 and T=0 pair-modes decouple in the exact calculations with the T=1
pair-energy being independent of the T=0 pair-strength and vice-versa. In the
rotating-field, the isoscalar correlations remain constant in contrast to the
well known quenching of isovector pairing. An increase of the isoscalar (J=1,
T=0) pair-field results in a delay of the bandcrossing frequency. This
behaviour is shown to be present only near the N=Z line and its experimental
confirmation would imply a strong signature for isoscalar pairing collectivity.
The solutions of the exact model are also discussed in the
Hartree-Fock-Bogoliubov approximation.Comment: 5 pages, 4 figures, submitted to PR
Systematics of g factors of 2_1^+ states in even-even nuclei from Gd to Pt: A microscopic description by the projected shell model
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.Comment: 9 pages, 5 figure