12,925 research outputs found
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
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
Momentum distributions and spectroscopic factors of doubly-closed shell nuclei in correlated basis function theory
The momentum distributions, natural orbits, spectroscopic factors and
quasi-hole
wave functions of the C12, O16, Ca40, Ca48, and Pb208 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 the realistic Argonne v8' nucleon-nucleon
potential, together with the Urbana IX three-body interaction. Operator
dependent correlations, which consider channels up to the tensor ones, have
been
used. We found noticeable effects produced by the correlations. For high
momentum values, the momentum distributions show large enhancements with
respect to the independent particle model results. Natural orbits occupation
numbers are depleted by about the 10\% with respect to the independent particle
model values. The effects of the correlations on the spectroscopic factors are
larger on the more deeply bound states.Comment: Modified version of the previous paper (there are new figures). The
paper has been accepted for publication in Physical Review
Correlations and charge distributions of medium heavy nuclei
The effects of long- and short-range correlations on the charge distributions
of some medium and heavy nuclei are investigated. The long-range correlations
are treated within the Random Phase Approximation framework and the short-range
correlations with a model inspired to the Correlation Basis Function theory.
The two type of correlations produce effects of the same order of magnitude. A
comparison with the empirical charge distribution difference between 206Pb and
205Tl shows the need of including both correlations to obtain a good
description of the data.Comment: 20 pages, Latex, accepted for publication in Jour. Phys.
Mean-field calculations of exotic nuclei ground states
We study the predictions of three mean-field theoretical approaches in the
description of the ground state properties of some spherical nuclei far from
the stability line. We compare binding energies, single particle spectra,
density distributions, charge and neutron radii obtained with non-relativistic
Hartree-Fock calculations carried out with both zero and finite-range
interactions, and with a relativistic Hartree approach which uses a
finite-range interaction. The agreement between the results obtained with the
three different approaches indicates that these results are more related to the
basic hypotheses of the mean-field approach rather than to its implementation
in actual calculations.Comment: 16 pages, 12 figures, 2 tables, accepted for publication in Physical
Review
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