180 research outputs found
Nuclear single-particle states: dynamical shell model and energy density functional methods
We discuss different approaches to the problem of reproducing the observed
features of nuclear single-particle (s.p.) spectra. In particular, we analyze
the dominant energy peaks, and the single-particle strength fragmentation,
using the example of neutron states in 208Pb. Our main emphasis is the
interpretation of that fragmentation as due to particle-vibration coupling
(PVC). We compare with recent Energy Density Functional (EDF) approaches, and
try to present a critical perspective.Comment: 7 pages. Contribution to the "Focus issue on Open Problems in Nuclear
Structure", Journal of Physics
Giant resonances in exotic spherical nuclei within the RPA approach with the Gogny force
Theoretical results for giant resonances in the three doubly magic exotic
nuclei Ni, Sn and Sn are obtained from Hartree-Fock (HF)
plus Random Phase Approximation (RPA) calculations using the D1S
parametrization of the Gogny two-body effective interaction. Special attention
is paid to full consistency between the HF field and the RPA particle-hole
residual interaction. The results for the exotic nuclei, on average, appear
similar to those of stable ones, especially for quadrupole and octupole states.
More exotic systems have to be studied in order to confirm such a trend. The
low energy of the monopole resonance in Ni suggests that the compression
modulus in this neutron rich nucleus is lower than the one of stable ones.Comment: 16 pages, 10 figure
The halo of the exotic nucleus 11Li: a single Cooper pair
If neutrons are progressively added to a normal nucleus, the Pauli principle
forces them into states of higher momentum. When the core becomes
neutron-saturated, the nucleus expels most of the wavefunction of the last
neutrons outside to form a halo, which because of its large size can have lower
momentum. It is an open question how nature stabilizes such a fragile system
and provides the glue needed to bind the halo neutrons to the core. Here we
show that this problem is similar to that of the instability of the normal
state of an electron system at zero temperature solved by Cooper, solution
which is at the basis of BCS theory of superconductivity. By mimicking this
approach using, aside from the bare nucleon-nucleon interaction, the long
wavelength vibrations of the nucleus Li, the paradigm of halo nuclei, as
tailored glues of the least bound neutrons, we are able to obtain a unified and
quantitative picture of the observed properties of Li.Comment: 16 pages, 1 b/w figures, 2 colour figure
The Spectral Line Shape of Exotic Nuclei
The quadrupole strength function of is calculated making use of the
SIII interaction, within the framework of continuum-RPA and taking into account
collisions among the nucleons (doorway coupling). The centroid of the giant
resonance is predicted at MeV, that is much below the energy
expected for both isoscalar and isovector quadrupole resonances in nuclei along
the stability valley. About half of this width arises from the coupling of the
resonance to the continuum and about half is due to doorway coupling. This
result is similar to that obtained in the study of giant resonances in light,
-stable nuclei, and shows the lack of basis for the expectation,
entertained until now in the literature, that continuum decay was the main
damping mechanism of giant resonances in halo nuclei.Comment: LaTeX file, 7 pages, figures not included but available if requested
at [email protected], accepted for publication in Phys. Rev.
The fully self-consistent quasiparticle random phase approximation and its application to the isobaric analog resonances
A microscopic model aimed at the description of charge-exchange nuclear
excitations along isotopic chains which include open-shell systems, is
developed. It consists of quasiparticle random phase approximation (QRPA) made
on top of Hartree-Fock-Bardeen-Cooper-Schrieffer (HF-BCS). The calculations are
performed by using the Skyrme interaction in the particle-hole channel and a
zero-range, density-dependent pairing force in the particle-particle channel.
At variance with the (many) versions of QRPA which are available in literature,
in our work special emphasis is put on the full self-consistency. Its
importance, as well as the role played by the charge-breaking terms of the
nuclear Hamiltonian, like the Coulomb interaction, the charge symmetry and
charge independence breaking (CSB-CIB) forces and the electromagnetic
spin-orbit, are elucidated by means of numerical calculations of the isobaric
analog resonances (IAR). The theoretical energies of these states along the
chain of the Sn isotopes agree well with the experimental data in the stable
isotopes. Predictions for unstable systems are presented.Comment: 15 pages, 6 figure
Towards a Unified Description of Isoscalar Giant Monopole Resonances in a Self-Consistent Quasiparticle-Vibration Coupling Approach
"Why is the EoS for tin so soft?" is a longstanding question, which prevents
us from determining the nuclear incompressibility accurately. To
solve this puzzle, a fully self-consistent quasiparticle random phase
approximation (QRPA) plus quasiparticle-vibration coupling (QPVC) approach
based on Skyrme-Hartree-Fock-Bogoliubov is developed. We show that the
many-body correlations introduced by QPVC, which shift the ISGMR energy in Sn
isotopes by about 0.4 MeV more than the energy in Pb, play a crucial
role in providing a unified description of the ISGMR in Sn and Pb isotopes. The
best description of the experimental strength functions is given by SV-K226 and
KDE0, which are characterized by incompressibility values 226 MeV
and 229 MeV, respectively, at mean field level
Effects of the Tensor Force on the Multipole Response in Finite Nuclei
We present a thorough analysis of the effects of the tensor interaction on
the multipole response of magic nuclei, using the fully self-consistent Random
Phase Approximation (RPA) model with Skyrme interactions. We disentangle the
modifications to the static mean field induced by the tensor terms, and the
specific features of the residual particle-hole (p-h) tensor interaction, for
quadrupole (2+), octupole (3-), and also magnetic dipole (1+) responses. It is
pointed out that the tensor force has a larger effect on the magnetic dipole
states than on the natural parity states 2+ and 3-, especially at the mean
field level. Perspectives for a better assessment of the tensor force
parameters are eventually discussed
Giant Quadrupole Resonances in 208Pb, the nuclear symmetry energy and the neutron skin thickness
Recent improvements in the experimental determination of properties of the
Isovector Giant Quadrupole Resonance (IVGQR), as demonstrated in the A=208 mass
region, may be instrumental for characterizing the isovector channel of the
effective nuclear interaction. We analyze properties of the IVGQR in 208Pb,
using both macroscopic and microscopic approaches. The microscopic method is
based on families of non-relativistic and covariant Energy Density Functionals
(EDF), characterized by a systematic variation of isoscalar and isovector
properties of the corresponding nuclear matter equations of state. The
macroscopic approach yields an explicit dependence of the nuclear symmetry
energy at some subsaturation density, for instance S(\rho=0.1 fm^{-3}), or the
neutron skin thickness \Delta r_{np} of a heavy nucleus, on the excitation
energies of isoscalar and isovector GQRs. Using available data it is found that
S(\rho=0.1 fm{}^{-3})=23.3 +/- 0.6 MeV. Results obtained with the microscopic
framework confirm the correlation of the \Delta r_{np} to the isoscalar and
isovector GQR energies, as predicted by the macroscopic model. By exploiting
this correlation together with the experimental values for the isoscalar and
isovector GQR energies, we estimate \Delta r_{np} = 0.14 +/- 0.03 fm for 208Pb,
and the slope parameter of the symmetry energy: L = 37 +/- 18 MeV
Medium polarization isotopic effects on nuclear binding energies
There exist several effective interactions whose parameters are fitted to
force mean field predictions to reproduce experimental findings of finite
nuclei and calculated properties of infinite nuclear matter. Exploiting this
tecnique one can give a good description of nuclear binding energies. We
present evidence that further progress can be made by taking into account
medium polarization effects associated with surface and pairing vibrations.Comment: 7 pages, 5 figure
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