1,196 research outputs found
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.
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
Testing instantaneous causality in presence of non constant unconditional variance
The problem of testing instantaneous causality between variables with
time-varying unconditional variance is investigated. It is shown that the
classical tests based on the assumption of stationary processes must be avoided
in our non standard framework. More precisely we underline that the standard
test does not control the type I errors, while the tests with White (1980) and
Heteroscedastic Autocorrelation Consistent (HAC) corrections can suffer from a
severe loss of power when the variance is not constant. Consequently a modified
test based on a bootstrap procedure is proposed. The relevance of the modified
test is underlined through a simulation study. The tests considered in this
paper are also compared by investigating the instantaneous causality relations
between US macroeconomic variables.Comment: Keywords : VAR model, Unconditionally heteroscedastic errors,
instantaneous causalit
A self-consistent QRPA study of quadrupole collectivity around 32Mg
On the basis of the Hartree-Fock-Bogoliubov (HFB) plus quasiparticle random
phase approximation method (QRPA) based on the Green's function approach with
Skyrme force, we discuss the anomalous E2 properties of the first 2+ states in
neutron-rich nuclei 32Mg and 30Ne. The B(E2) values and the excitation energies
of the first 2+ states are well described within HFB plus QRPA calculations
with spherical symmetry. We conclude that pairing effects account largely for
the anomalously large B(E2) values and the low excitation energies in 32Mg and
30Ne.Comment: 5 pages, 5 figures, Proceedings of the international symposium "A new
era of nuclear structure physics", 19-22 November 2003, Niigata, Japa
Isospin corrections for superallowed Fermi beta decay in self-consistent relativistic random phase approximation approaches
Self-consistent random phase approximation (RPA) approaches in the
relativistic framework are applied to calculate the isospin symmetry-breaking
corrections for the superallowed transitions. It is
found that the corrections are sensitive to the proper treatments of
the Coulomb mean field, but not so much to specific effective interactions.
With these corrections , the nucleus-independent
values are obtained in combination with the experimental values in the
most recent survey and the improved radiative corrections. It is found that the
constancy of the values is satisfied for all effective
interactions employed. Furthermore, the element and unitarity of the
Cabibbo-Kobayashi-Maskawa matrix are discussed.Comment: 7 pages, 2 figures, 4 table
Nuclear structure calculations with a separable approximation for Skyrme interactions
A finite rank separable approximation for the quasiparticle RPA calculations
with Skyrme interactions that was proposed in our previous work is extended to
take into account the coupling between one- and two-phonon terms in the wave
functions of excited states. It is shown that characteristics calculated within
the suggested approach are in a good agreement with available experimental
data.Comment: 6 pages, proceedings of the International Symposium on Physics of
Unstable Nuclei (ISPUN02), Halong Bay, Vietnam, November 20-25, 200
RPA Correlations and Nuclear Densities in Relativistic Mean Field Approach
The relativistic mean field approach (RMF) is well known for describing
accurately binding energies and nucleon distributions in atomic nuclei
throughout the nuclear chart. The random phase approximation (RPA) built on top
of the RMF is also a good framework for the study of nuclear excitations. Here,
we examine the consequences of long range correlations brought about by the RPA
on the neutron and proton densities as given by the RMF approach.Comment: 15 pages, 13 figure
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
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
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