222 research outputs found
Theoretical understanding of the nuclear incompressibility: where do we stand ?
The status of the theoretical research on the compressional modes of finite
nuclei and the incompressibility of nuclear matter, is reviewed. It
is argued that the recent experimental data on the Isoscalar Giant Monopole
Resonance (ISGMR) allow extracting the value of with an uncertainity
of about 12 MeV. Non-relativistic (Skyrme, Gogny) and relativistic mean
field models predict for values which are significantly different
from one another, namely 220-235 and 250-270 MeV
respectively. It is shown that the solution of this puzzle requires a better
determination of the symmetry energy at, and around, saturation. The role
played by the experimental data of the Isoscalar Giant Dipole Resonance (ISGDR)
is also discussed.Comment: To appear in the proceedings of the COMEX1 conference (special issue
of Nucl. Phys. A). Few changes and corrections compared to the previous
version. General conclusion unchange
Equation of state in the inner crust of neutron stars: discusion of the unbound neutron states
In this paper, we calculate the stable Wigner-Seitz (W-S) cells in the inner
crust of neutron stars and we discuss the nuclear shell effects. A distinction
is done between the shell effects due to the bound states and those induced by
the unbound states, which are shown to be spurious. We then estimate the
effects of the spurious shells on the total energy and decompose it into a
smooth and a residual part. We propose a correction to the Hartree-Fock binding
energy in Wigner-Seitz cell (HF-WS).Comment: conference EXOCT07, Catania, 11-15 June, 200
Proton decay of high-lying states in odd nuclei
In the framework of the quasiparticle-phonon model, we study the
non-statistical proton decay of excited states in odd nuclei towards low-lying
collective states. Partial cross sections and branching ratios for the proton
decay of the high angular momentum states in Sc, Cu and Nb
%{\it excited by means of the (Li,He) reaction} are evaluated. The
calculated branching ratios predict strong direct proton decays to the
low-lying vibrational states in Sc and Nb. A general agreement
with existing experimental data is found.Comment: 12 pages, 2 figures, Latex, accepted for publication in Nucl. Phys.
Pairing interactions and the vanishing pairing correlations in hot nuclei
Finite temperature Hartree-Fock-Bogoliubov calculations are performed in Sn
isotopes using Skyrme and zero-range, density-dependent pairing interactions.
For both stable and very neutron-rich nuclei the critical temperature at which
pairing correlations vanish is independent of the volume/surface nature of the
pairing interaction. The value of the critical temperature follows
approximatively the empirical rule T 0.5 for all
the calculated isotopes, showing that the critical temperature could be deduced
from the pairing gap at zero temperature. On the other hand, the pairing gap at
temperatures just below T is strongly sensitive to the volume/surface
nature of the pairing interaction.Comment: 6 pages, 7 figures revised versio
Treatment of pairing correlations in nuclei close to drip lines
We discuss the HFB equations in coordinate representation,a suitable method
for handling the full effects of the continuous quasiparticle spectrum. We show
how the continuum HFB equations can be solved with the correct asymptotic
conditions instead of the discretization conditions which are commonly used in
the literature. The continuum HFB method is illustrated with a model where the
mean field and pairing field have simple forms. The relationship with the
continuum Hartree-Fock-BCS (HF-BCS) approximation is also discussed. Realistic
HFB and HF-BCS calculations based on Skyrme interactions are compared for the
case of a neutron-rich nucleus.Comment: 12 pages, 4 Postscript figures, uses KapProc.cls, to appear in
Proceedings of NATO School " Nuclei far from stability and astrophysics",
Predeal, Romania, 200
Superfluid Properties of the Inner Crust of Neutron Stars
Superfluid properties of the inner crust matter of neutron stars, formed by
nuclear clusters immersed in a dilute neutron gas, are analysed in a self-
consistent HFB approach. The calculations are performed with two pairing
forces, fixed so as to obtain in infinite nuclear matter the pairing gaps
provided by the Gogny force or by induced interactions. It is shown that the
nuclear clusters can either suppress or enhance the pairing correlations inside
the inner crust matter, depending on the density of the surrounding neutrons.
The profile of the pairing field in the inner crust is rather similar for both
pairing forces, but the values of the pairing gaps are drastically reduced for
the force which simulates the polarisation effects in infinite neutron matter.Comment: 13 pages, 6 figures. Corrected typos and new format. To appear in
Phys. Rev.
Convergence of Particle-Hole Expansions for the Description of Nuclear Correlations
The convergence properties of a multiparticle-multihole (mp-mh) configuration
mixing approach whose purpose is to describe ground state correlations in
nuclei without particle number and Pauli violations is investigated in the case
of an exactly solvable pairing hamiltonian. Two different truncation schemes
are tested by looking at quantities as correlation energies and single-particle
occupation probabilities. Results show that pairing correlations present in
usual superfluid nuclei can be accurately described using up to 6 particle-6
hole excitations, a convergence fast enought for envisaging extensions to fully
microscopic calculations.Comment: 8 pages, 4 figure
Effects of the tensor force on the ground and first states of the magic Ca nucleus
The magic nature of the Ca nucleus is investigated in the light of the
recent experimental results. We employ both HFB and HF+BCS methods using
Skyrme-type SLy5, SLy5+T and T44 interactions. The evolution of the
single-particle spectra is studied for the N=34 isotones: Fe, Cr,
Ti and Ca. An increase is obtained in the neutron spin-orbit
splittings of and states due to the effect of the tensor force which
also makes Ca a magic nucleus candidate. QRPA calculations on top of
HF+BCS are performed to investigate the first = states of the
calcium isotopic chain. A good agreement for excitation energies is obtained
when we include the tensor force in the mean-field part of the calculations.
The first states indicate a subshell closure for both Ca and
Ca nuclei. We confirm that the tensor part of the interaction is quite
essential in explaining the neutron subshell closure in Ca and Ca
nuclei.Comment: 8 pages, 3 figure
Neutrino propagation in Neutron Matter and the Nuclear Equation of State
We study the propagation of neutrinos inside dense matter under the
conditions prevailing in a proto-neutron star. Equations of state obtained with
different nuclear effective interactions (Skyrme type and Gogny type) are first
discussed. It is found that for many interactions, spin and/or isospin
instabilities occur at densities larger than the saturation density of nuclear
matter. From this study we select two representative interactions, SLy230b and
D1P. We calculate the response functions in pure neutron matter where nuclear
correlations are described at the Hartree-Fock plus RPA level. These response
functions allow us to evaluate neutrino mean free paths corresponding to
neutral current processes.Comment: 8 pages, 7 figures, to appear in "The Nuclear Many-Body Problem
2001", NATO Science Series II (Kluwer Academic Publishers
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
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