438 research outputs found
Effect of Tensor Correlations on Gamow-Teller States in 90Zr and 208Pb
The tensor terms of the Skyrme effective interaction are included in the
self-consistent Hartree-Fock plus Random Phase Approximation (HF+RPA) model.
The Gamow-Teller (GT) strength function of 90Zr and 208Pb are calculated with
and without the tensor terms. The main peaks are moved downwards by about 2 MeV
when including the tensor contribution. About 10% of the non-energy weighted
sum rule is shifted to the excitation energy region above 30 MeV by the RPA
tensor correlations. The contribution of the tensor terms to the energy
weighted sum rule is given analytically, and compared to the outcome of RPA.Comment: 13 pages, 2 figures,2 table
Particle-drip lines from the Hartree-Fock-Bogoliubov theory with Skyrme interaction
We calculate positions of one- and two-particle, proton and neutron drip
lines within the Hartree-Fock-Bogoliubov theory using Skyrme interaction. We
also determine an approximate -process path defined as a line where the
neutron binding energy is equal to 2~MeV. A weakening of the nuclear shell
structure at drip lines is found and interpreted as resulting from a coupling
with continuum states.Comment: 10 pages REVTEX 3.0, 3 uuencoded postscript figures included,
IFT/14/9
Cross sections for the excitation of isovector charge-exchange resonances in 208Tl
The Glauber approximation for the treatment of heavy-ion scattering, has
already been shown to give reliable predictions for the reaction cross section
in the particular case of intermediate energy charge-exchange processes. In the
present work, we couple a Glauber-type model to microscopic Random Phase
Approximation calculations of the charge-exchange excitations of Pb.
The aim is to solve the longstanding question whether the very elusive
charge-exchange isovector monopole has been really identified in the past
experiments, or other multipoles were prevalent in the observed spectra.Comment: text + 4 figures; accepted for publication in Phys. Rev.
Spin-orbit interaction in Hartree-Fock calculations
The contribution of the spin-orbit interaction in Hartree-Fock calculations
for closed shell nuclei is studied. We obtain explicit expressions for the
finite range spin-orbit force. New terms with respect to the traditional
spin-orbit expressions are found. The importance of the finite-range is
analyzed. Results obtained with spin-orbit terms taken from realistic
interactions are presented. The effect of the spin-orbit isospin dependent
terms is evaluated.Comment: To be published on Nuovo Cimento
Widths of Isobaric Analog Resonances: a microscopic approach
A self-consistent particle-phonon coupling model is used to investigate the
properties of the isobaric analog resonance in Bi. It is shown that
quantitative agreement with experimental data for the energy and the width can
be obtained if the effects of isospin-breaking nuclear forces are included, in
addition to the Coulomb force effects. A connection between microscopic model
predictions and doorway state approaches which make use of the isovector
monopole resonance, is established via a phenomenological ansatz for the
optical potential.Comment: 18 pages, 1 figure. To appear on Phys. Rev. C (tentatively scheduled
for June 1998
A unique spinodal region in asymmetric nuclear matter
Asymmetric nuclear matter at sub-saturation densities is shown to present
only one type of instabilities. The associated order parameter is dominated by
the isoscalar density and so the transition is of liquid-gas type. The
instability goes in the direction of a restoration of the isospin symmetry
leading to a fractionation phenomenon. These conclusions are model independent
since they can be related to the general form of the asymmetry energy. They are
illustrated using density functional approaches.Comment: 4 pages, 5 figures, to appear in Phys. Rev.
Quasiparticle RPA with finite rank approximation for Skyrme interactions
A finite rank separable approximation for the particle-hole RPA calculations
with Skyrme interactions is extended to take into account the pairing. As an
illustration of the method energies and transition probabilities for the
quadrupole and octupole excitations in some O, Ar, Sn and Pb isotopes are
calculated. The values obtained within our approach are very close to those
that were calculated within QRPA with the full Skyrme interaction. They are in
reasonable agreement with experimental data.Comment: 20 pages, 1 figure, submitted to Phys.Rev.
Probing coherent charmonium photoproduction off light nuclei at medium energies
We demonstrate how the elementary amplitudes , the
amplitude of the nondiagonal transition, and
the total and cross sections can be determined from
measurements of the coherent and photoproduction off light
nuclei at moderate energies. For this purpose we provide a detailed numerical
analysis of the coherent charmonium photoproduction off silicon within the
generalized vector dominance model (GVDM) adjusted to account for the physics
of charmonium models and color transparency phenomenon.Comment: 8 pages, 5 figures (color
Continuum quasiparticle random phase approximation and the time dependent Hartree-Fock-Bogoliubov approach
Quadrupole excitations of neutron-rich nuclei are analyzed by using the
linear response method in the Quasiparticle Random Phase Approximation (QRPA).
The QRPA response is derived starting from the time-dependent
Hartree-Fock-Bogoliubov (HFB) equations. The residual interaction between the
quasiparticles is determined consistently from the two-body force used in the
HFB equations, and the continuum coupling is treated exactly.
Calculations are done for the neutron-rich oxygen isotopes. It is found that
pairing correlations affect the low-lying states, and that a full treatment of
the continuum can change the structure of the states in the giant resonance
region.Comment: 17 pages, 7 figures. Revised version with comments and references
adde
Particles in classically forbidden area, neutron skin and halo, and pure neutron matter in Ca isotopes
The nucleon density distributions and the thickness of pure neutron matter in
Ca isotopes were systematically studied using the Skyrme-Hartree-Fock model
(SHF) from the -stability line to the neutron drip-line. The pure
neutron matter, related with the neutron skin or halo, was shown to depend not
only on the Fermi levels of the neutrons but also on the orbital angular
momentum of the valence neutrons. New definitions for the thickness of pure
neutron matter are proposed.Comment: 6 pages, 5 figure
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