103 research outputs found
Influence of complex configurations on properties of pygmy dipole resonance in neutron-rich Ca isotopes
Starting from the quasiparticle random phase approximation based on the
Skyrme interaction SLy5, we study the effects of phonon-phonon coupling~(PPC)
on the low-energy electric dipole response in Ca. Using the same set
of parameters we describe available experimental data for Ca and
give prediction for Ca. The inclusion of the PPC results in the
formation of low-energy states. There is an impact of the PPC effect on
low-energy ~strength of Ca. The PPC effect on the electric
dipole polarizability is discussed. We predict a strong increase of the summed
~strength below 10MeV, with increasing neutron number from Ca till
Ca.Comment: 11 pages, 10 figure
Structure of low-lying quadrupole states in nuclei near 132Sn
The properties of the low-lying 2^+ states in the even-even nuclei around
132Sn are studied within the quasiparticle random phase approximation. Starting
from a Skyrme interaction in the particle-hole channel and a density-dependent
zero-range interaction in the particle-particle channel, we use the finite rank
separable approach in our investigation. It is found that the fourth 2^+ state
in 132Te could be a good candidate for a mixed-symmetry state.Comment: 6 pages, 2 figures, proceedings of International Conference on
Nuclear Structure and Related Topics (NSRT09), June 2009, JINR, Dubna, Russi
Influence of 2p-2h configurations on beta-decay rates
The effects of the phonon-phonon coupling on the beta-decay rates of
neutron-rich nuclei are studied in a microscopic model based on Skyrme-type
interactions. The approach uses a finite-rank separable approximation of the
Skyrme-type particle-hole (p-h) residual interaction. Very large
two-quasiparticle spaces can thus be treated. A redistribution of the
Gamow-Teller (G-T) strength is found due to the tensor correlations and the
2p-2h fragmentation of G-T states. As a result, the beta-decay half-lives are
decreased significantly. Using the Skyrme interaction SGII together with a
volume-type pairing interaction we illustrate this reduction effect by
comparing with available experimental data for the Ni isotopes and neutron-rich
N=50 isotones. We give predictions for 76Fe and 80Ni in comparison with the
case of the doubly-magic nucleus 78Ni which is an important waiting point in
the r-process.Comment: 8 pages, 6 figures, accepted for publication in Physical Review
TDDFT with Skyrme Forces: Effect of Time-Odd Densities on Electric Giant Resonances
Time-odd densities and their effect on electric giant resonances are
investigated within the self-consistent separable random-phase-approximation
(SRPA) model for various Skyrme forces (SkT6, SkO, SkM*, SIII, SGII, SLy4,
SLy6, SkI3). Time-odd densities restore Galilean invariance of the Skyrme
functional, violated by the effective-mass and spin-orbital terms. In even-even
nuclei these densities do not contribute to the ground state but can affect the
dynamics. As a particular case, we explore the role of the current density in
description of isovector E1 and isoscalar E2 giant resonances in a chain of Nd
spherical and deformed isotopes with A=134-158. Relation of the current to the
effective masses and relevant parameters of the Skyrme functional is analyzed.
It is shown that current contribution to E1 and E2 resonances is generally
essential and fully determined by the values and signs of the isovector and
isoscalar effective-mass parameters of the force. The contribution is the same
for all the isotope chain, i.e. for both standard and exotic nuclei.Comment: 14 pages, 7 figures, will be published in Proceed. of 14th Nuclear
Physics Workshop (Kazimierez, Poland, September, 2007) Comment: latex error
in openning Fig. 2 was correcte
Evolution of Nuclear Shell Structure due to the Pion Exchange Potential
The evolution of nuclear shell structure is investigated for the first time
within density-dependent relativistic Hartree-Fock theory and the role of
-exchange potential is studied in detail. The energy differences between
the neutron orbits \Lrb{\nu1h_{9/2},\nu 1i_{13/2}} in the N=82 isotones and
between the proton ones \Lrb{\pi1g_{7/2},\pi1h_{11/2}} in the Z=50 isotopes
are extracted as a function of neutron excess . A kink around for
the N=82 isotones is found as an effect resulting from pion correlations. It is
shown that the inclusion of -coupling plays a central role to provide
realistic isospin dependence of the energy differences. In particular, the
tensor part of the -coupling has an important effect on the characteristic
isospin dependence observed in recent experiments.Comment: 4 pages and 4 figure
Dirac-Brueckner Hartree-Fock Approach: from Infinite Matter to Effective Lagrangians for Finite Systems
One of the open problems in nuclear structure is how to predict properties of
finite nuclei from the knowledge of a bare nucleon-nucleon interaction of the
meson-exchange type. We point out that a promising starting point consists in
Dirac-Brueckner-Hartree-Fock (DBHF) calculations us- ing realistic
nucleon-nucleon interactions like the Bonn potentials, which are able to
reproduce satisfactorily the properties of symmetric nuclear matter without the
need for 3-body forces, as is necessary in non-relativistic BHF calculations.
However, the DBHF formalism is still too com- plicated to be used directly for
finite nuclei. We argue that a possible route is to define effective
Lagrangians with density-dependent nucleon-meson coupling vertices, which can
be used in the Relativistic Hartree (or Relativistic Mean Field (RMF)) or
preferrably in the Relativistic Hartree- Fock (RHF) approach. The
density-dependence is matched to the nuclear matter DBHF results. We review the
present status of nuclear matter DBHF calculations and discuss the various
schemes to construct the self-energy, which lead to differences in the
predictions. We also discuss how effective Lagrangians have been constructed
and are used in actual calculations. We point out that completely consistent
calculations in this scheme still have to be performed.Comment: 16 pages, to be published in Journal of Physics G: Nuclear and
Particle Physics, special issue
Separabelized Skyrme Interactions and Quasiparticle RPA
A finite rank separable approximation for the quasiparticle RPA with Skyrme
interactions is applied to study the low lying quadrupole and octupole states
in some S isotopes and giant resonances in some spherical nuclei. It is shown
that characteristics calculated within the suggested approach are in a good
agreement with available experimental data.Comment: 12 pages, 2 figures, proceedings of the Seventh School-Seminar on
Heavy Ion Physics, Dubna, Russia, May 27-June 1, 2002; to appear in Physics
of Atomic Nucle
Escape and Spreading Properties of Charge-Exchange Resonances in Bi 208
The properties of charge-exchange excitations of Pb with , i.e., the isobaric analog and Gamow-Teller resonances, are studied within
a self-consistent model making use of an effective force of the Skyrme type.
The well-known isobaric analog case is used to assess the reliability of the
model. The calculated properties of the Gamow-Teller resonance are compared
with recent experimental measurements with the aim of better understanding the
microscopic structure of this mode.Comment: 26 pages including references, figure captions and tables. Figures
are available upon request at [email protected] (decnet 32858::COLO).
Preprint code: IPNO/TH 94-2
Pairing and continuum effects in nuclei close to the drip line
The Hartree-Fock-Bogoliubov (HFB) equations in coordinate representation are
solved exactly, i.e., with correct asymptotic boundary conditions for the
continuous spectrum. The calculations are preformed with effective Skyrme
interactions. The exact HFB solutions are compared with HFB calculations based
on box boundary conditions and with resonant continuum Hartree-Fock-BCS
(HF-BCS) results. The comparison is done for the neutron-rich Ni isotopes. It
is shown that close to the drip line the amount of pairing correlations depends
on how the continuum coupling is treated. On the other hand, the resonant
continuum HF-BCS results are generally close to those of HFB even in
neutron-rich nuclei.Comment: 9 figures, corrected ref.
Microscopic description of Coulomb and nuclear excitation of multiphonon states in Ca + Ca collisions
We calculate the inelastic scattering cross sections to populate one- and
two-phonon states in heavy ion collisions with both Coulomb and nuclear
excitations. Starting from a microscopic approach based on RPA, we go beyond it
in order to treat anharmonicities and non-linear terms in the exciting field.
These anharmonicities and non-linearities are shown to have important effects
on the cross sections both in the low energy part of the spectrum and in the
energy region of the Double Giant Quadrupole Resonance. By properly introducing
an optical potential the inelastic cross section is calculated semiclassically
by integrating the excitation probability over all impact parameters. A
satisfactory agreement with the experimental results is obtained.Comment: 20 pages, 2 figures, revtex, to be published in Phys. Rev.
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