16,950 research outputs found
Effective tensor forces and neutron rich nuclei
We study the effects of the tensor term of the effective nucleon-nucleon
interaction on nuclear excited states. Our investigation has been conducted by
using a self-consistent Random Phase Approximation approach. We investigate
various nuclei in different regions of the isotopes chart. Results for a set of
calcium isotopes are shown.Comment: 4 pages, 4 figures, 1 table Proc. 10th International Spring Seminar
on Nuclear Physics New Quests in Nuclear Structure, Vietri Sul Mare, May
21-25, 201
New Results in the CBF theory for medium-heavy nuclei
Momentum distributions, spectroscopic factors and quasi-hole wave functions
of medium-heavy doubly closed shell nuclei have been calculated in the
framework of the Correlated Basis Function theory, by using the Fermi
hypernetted chain resummation techniques. The calculations have been done by
using microscopic two-body nucleon-nucleon potentials of Argonne type, together
with three-body interactions. Operator dependent correlations, up to the tensor
channels, have been used.Comment: 6 pages, 3 figures, proceeding of the "XI Convegno su problemi di
Fisica Nucleare Teorica" 11-14 Ottobre 2006, Cortona, Ital
Nuclear re-interaction effects in quasi-elastic neutrino nucleus scattering
The quasi-elastic neutrino-nucleus cross section has been calculated by using
a Fermi gas model corrected to consider the re-scattering between the emitted
nucleon and the rest nucleus. As an example of the relevance of this effect we
show results for the muon production cross section on 16O target.Comment: 7 pages, 4 Postscript figures, Contribution to NuInt01 Workshop, KEK,
Tsukuba, Japa
Ground state of medium-heavy doubly-closed shell nuclei in correlated basis function theory
The correlated basis function theory is applied to the study of medium-heavy
doubly closed shell nuclei with different wave functions for protons and
neutrons and in the jj coupling scheme. State dependent correlations including
tensor correlations are used. Realistic two-body interactions of Argonne and
Urbana type, together with three-body interactions have been used to calculate
ground state energies and density distributions of the 12C, 16O, 40Ca, 48Ca and
208Pb nuclei.Comment: Latex 10 pages, 3 Tables, 10 Figure
Renormalized Fermi hypernetted chain approach in medium-heavy nuclei
The application of the Correlated basis function theory and of the Fermi
hypernetted chain technique, to the description of the ground state of
medium-heavy nuclei is reviewed. We discuss how the formalism, originally
developed for symmetric nuclear matter, should be changed in order to describe
finite nuclear systems, with different number of protons and neutrons. This
approach allows us to describe doubly closed shell nuclei by using microscopic
nucleon-nucleon interactions. We presents results of numerical calculations
done with two-nucleon interactions of Argonne type,implemented with three-body
forces of Urbana type. Our results regard ground-state energies, matter, charge
and momentum distributions, natural orbits, occupation numbers, quasi-hole wave
functions and spectroscopic factors of 12C, 16O, 40Ca, 48Ca and 208Pb nuclei.Comment: 127 Pages, 37 figures, Accepted for publication in Physics Report
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.
Evolution of the pygmy dipole resonance in nuclei with neutron excess
The electric dipole excitation of various nuclei is calculated with a Random
Phase Approximation phenomenological approach. The evolution of the strength
distribution in various groups of isotopes, oxygen, calcium, zirconium and tin,
is studied. The neutron excess produces strength in the low energy region.
Indexes to measure the collectivity of the excitation are defined. We studied
the behavior of proton and neutron transition densities to determine the
isoscalar or isovector nature of the excitation. We observed that in
medium-heavy nuclei the low-energy excitation has characteristics rather
different that those exhibited by the giant dipole resonance. This new type of
excitation can be identified as pygmy dipole resonance.Comment: 14 pages, 12 figures, 7 table
Effects of state dependent correlations on nucleon density and momentum distributions
The proton momentum and density distributions of closed shell nuclei are
calculated within a model treating short--range correlations up to first order
in the cluster expansion. The validity of the model is verified by comparing
the results obtained with purely scalar correlations with those produced by
finite nuclei Fermi Hypernetted Chain calculations. State dependent
correlations are used to calculate momentum and density distributions of 12C,
16O, 40Ca, and 48Ca, and the effects of their tensor components are studied.Comment: 16 pages, latex, 8 figures, accepted for publication in Phys. Rev.
Evolution of the pygmy dipole resonance in nuclei with neutron excess
The electric dipole excitation of various nuclei is calculated with a Random
Phase Approximation phenomenological approach. The evolution of the strength
distribution in various groups of isotopes, oxygen, calcium, zirconium and tin,
is studied. The neutron excess produces strength in the low energy region.
Indexes to measure the collectivity of the excitation are defined. We studied
the behavior of proton and neutron transition densities to determine the
isoscalar or isovector nature of the excitation. We observed that in
medium-heavy nuclei the low-energy excitation has characteristics rather
different that those exhibited by the giant dipole resonance. This new type of
excitation can be identified as pygmy dipole resonance.Comment: 14 pages, 12 figures, 7 table
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