21,019 research outputs found
Weak response of nuclei
We discuss some differences and similarities between electron and neutrino
scattering off atomic nuclei. We find that, in the giant resonance region, the
two processes excite different nuclear modes, therefore the weak and the
electromagnetic nuclear responses are rather different. In any case, the
scattering of electrons and photons is the best guide we have to test the
validity of our nuclear models and their prediction power. The experience in
describing electromagnetic excitations of the nucleus, suggests that, when the
nucleus is excited in the continuum, the re-interaction between the emitted
nucleon and the remaining nucleus should not be neglected. A simple model
taking into account this final state interaction is proposed, and applied to
the neutrino scattering off 16O nucleus.Comment: To appear in the proceedings of the workshop "Electron-Nucleus
Scattering VIII", Marciana Marina, Elba (It), jUNE 21-2
Proton emission induced by polarized photons
The proton emission induced by polarized photons is studied in the energy
range above the giant resonance region and below the pion emission threshold.
Results for the 12C, 16O and 40Ca nuclei are presented. The sensitivity of
various observables to final state interaction, meson exchange currents and
short range correlations is analyzed. We found relevant effects due to the
virtual excitation of the resonance.Comment: 12 pages, 11 figures, 1 tabl
Model calculations of doubly closed shell nuclei in CBF theory III. j-j coupling and isospin dependence
Correlated Basis Function theory and Fermi Hypernetted Chain technique are
extended to study medium-heavy, doubly closed shell nuclei in j-j coupling
scheme, with different single particle wave functions for protons and neutrons
and isospin dependent two-body correlations. Central semirealistic interactions
are used. Ground state energies, one-body densities, distribution functions and
momentum distributions are calculated for 12C, 16O, 40Ca, 48Ca and 208Pb
nuclei. The values of the ground state energies provided by isospin dependent
correlations are lower than those obtained with isospin independent
correlations. In finite nuclear systems, the two--body Euler equations provide
correlation functions variationally more effective than those obtained with the
same technique in infinite nuclear matter.Comment: 29 Latex pages plus 6 Postscript figure
A model of short-range correlations in the charge response
The validity of a model treating the short-range correlations up to the first
order is studied by calculating the charge response of an infinite system and
comparing the obtained results with those of a Fermi Hypernetted Chain
calculation.Comment: 6 pages, 3 Postscript figures, to be published on Phys. Rev.
Magnetic excitations in nuclei with neutron excess
The excitation of the , and modes in O, O,
O, O, Ca, Ca, Ca and Ca nuclei is
studied with self-consistent random phase approximation calculations.
Finite-range interactions of Gogny type, containing also tensor-isospin terms,
are used. We analyze the evolution of the magnetic resonances with the
increasing number of neutrons, the relevance of collective effects, the need of
a correct treatment of the continuum and the role of the tensor force.Comment: 18 pages, 12 figures, 2 tables, accepted for publication in Physical
Review
Low-lying magnetic excitations of doubly-closed-shell nuclei and nucleon-nucleon effective interactions
We have studied the low lying magnetic spectra of 12C, 16O, 40Ca, 48Ca and
208Pb nuclei within the Random Phase Approximation (RPA) theory, finding that
the description of low-lying magnetic states of doubly-closed-shell nuclei
imposes severe constraints on the spin and tensor terms of the nucleon-nucleon
effective interaction. We have first made an investigation by using four
phenomenological effective interactions and we have obtained good agreement
with the experimental magnetic spectra, and, to a lesser extent, with the
electron scattering responses. Then we have made self-consistent RPA
calculations to test the validity of the finite-range D1 Gogny interaction. For
all the nuclei under study we have found that this interaction inverts the
energies of all the magnetic states forming isospin doublets.Comment: 19 pages, 13 figures, 7 tables, accepted for publication in Phys.
Rev.
A study of self-consistent Hartree-Fock plus Bardeen-Cooper-Schrieffer calculations with finite-range interactions
In this work we test the validity of a Hartree-Fock plus
Bardeen-Cooper-Schrieffer model in which a finite-range interaction is used in
the two steps of the calculation by comparing the results obtained to those
found in a fully self-consistent Hartree-Fock-Bogoliubov calculations using the
same interaction.Specifically, we consider the Gogny-type D1S and D1M forces.
We study a wide range of spherical nuclei, far from the stability line, in
various regions of the nuclear chart, from oxygen to tin isotopes. We calculate
various quantities related to the ground state properties of these nuclei, such
as binding energies, radii, charge and density distributions and elastic
electron scattering cross sections. The pairing effects are studied by direct
comparison with the Hartree-Fock results. Despite of its relative simplicity,
in most of the cases, our model provides results very close to those of the
Hartree-Fock-Bogoliubov calculations, and it reproduces rather well the
empirical evidences of pairing effects in the nuclei investigated.Comment: 28 pages, 13 figures. Accepted for publication in J. Phys.
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