424 research outputs found
The Giant Dipole Resonance as a quantitative constraint on the symmetry energy
The possible constraints on the poorly determined symmetry part of the
effective nuclear Hamiltonians or effective energy functionals, i.e., the
so-called symmetry energy S(rho), are very much under debate. In the present
work, we show that the value of the symmetry energy associated with Skyrme
functionals, at densities rho around 0.1 fm^{-3}, is strongly correlated with
the value of the centroid of the Giant Dipole Resonance (GDR) in spherical
nuclei. Consequently, the experimental value of the GDR in, e.g., 208Pb can be
used as a constraint on the symmetry energy, leading to 23.3 MeV < S(rho=0.1
fm^{-3}) < 24.9 MeV.Comment: 5 pages, 2 figures, submitte
The Compression-Mode Giant Resonances and Nuclear Incompressibility
The compression-mode giant resonances, namely the isoscalar giant monopole
and isoscalar giant dipole modes, are examples of collective nuclear motion.
Their main interest stems from the fact that one hopes to extrapolate from
their properties the incompressibility of uniform nuclear matter, which is a
key parameter of the nuclear Equation of State (EoS). Our understanding of
these issues has undergone two major jumps, one in the late 1970s when the
Isoscalar Giant Monopole Resonance (ISGMR) was experimentally identified, and
another around the turn of the millennium since when theory has been able to
start giving reliable error bars to the incompressibility. However, mainly
magic nuclei have been involved in the deduction of the incompressibility from
the vibrations of finite nuclei. The present review deals with the developments
beyond all this. Experimental techniques have been improved, and new
open-shell, and deformed, nuclei have been investigated. The associated changes
in our understanding of the problem of the nuclear incompressibility are
discussed. New theoretical models, decay measurements, and the search for the
evolution of compressional modes in exotic nuclei are also discussed.Comment: Review paper to appear in "Progress in Particle and Nuclear Physics
Effects of phonon-phonon coupling on low-lying states in neutron-rich Sn isotopes
Starting from an effective Skyrme interaction we present a method to take
into account the coupling between one- and two-phonon terms in the wave
functions of excited states. The approach is a development of a finite rank
separable approximation for the quasiparticle RPA calculations proposed in our
previous work. The influence of the phonon-phonon coupling on energies and
transition probabilities for the low-lying quadrupole and octupole states in
the neutron-rich Sn isotopes is studied.Comment: 18 page
QRPA plus Phonon Coupling Model and the Photoabsorbtion Cross Section for O
We have calculated the electric dipole strength distributions in the unstable
neutron rich oxygen isotopes O, in a model which include up to
four quasi-particle-type configurations. The model is the extension, to include
the effect of the pairing correlations, of a previous model very successful
around closed shell nuclei, and it is based on the quasi-particle-phonon
coupling. Low-lying dipole strength is found, which exhausts between 5 and 10%
of the Thomas-Reiche-Kuhn (TRK) energy-weighted-sum-rule (EWSR) below 15 MeV
excitation energy, in rather good agreement with recent experimental data. The
role of the phonon coupling is shown to be crucial in order to obtain this
result.Comment: 16 pages + 6 figure
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
Symmetry energy from the nuclear collective motion: constraints from dipole, quadrupole, monopole and spin-dipole resonances
The experimental and theoretical studies of Giant Resonances, or more
generally of the nuclear collective vibrations, are a well established domain
in which sophisticated techniques have been introduced and firm conclusions
reached after an effort of several decades. From it, information on the nuclear
equation of state can be extracted, albeit not far from usual nuclear
densities. In this contribution, which complements other contributions
appearing in the current volume, we survey some of the constraints that have
been extracted recently concerning the parameters of the nuclear symmetry
energy. Isovector modes, in which neutrons and protons are in opposite phase,
are a natural source of information and we illustrate the values of symmetry
energy around saturation deduced from isovector dipole and isovector quadrupole
states. The isotopic dependence of the isoscalar monopole energy has also been
suggested to provide a connection to the symmetry energy: relevant theoretical
arguments and experimental results are thoroughly discussed. Finally, we
consider the case of the charge-exchange spin-dipole excitations in which the
sum rule associated with the total strength gives in principle access to the
neutron skin and thus, indirectly, to the symmetry energy.Comment: Updated version, with small corrections based on comments/suggestions
from the referee. 12 pages, 9 figures; submitted to EPJA "Special Issue on
Symmetry Energy
Skyrme functional with tensor terms from \textit{ab initio} calculations of neutron-proton drops
A new Skyrme functional devised to account well for standard nuclear
properties as well as for spin and spin-isospin properties is presented. The
main novelty of this work relies on the introduction of tensor terms guided by
\textit{ab initio} relativistic Brueckner-Hartree-Fock calculations of
neutron-proton drops. The inclusion of tensor term does not decrease the
accuracy in describing bulk properties of nuclei, experimental data of some
selected spherical nuclei such as binding energies, charge radii, and
spin-orbit splittings can be well fitted. The new functional is applied to the
investigation of various collective excitations such as the Giant Monopole
Resonance (GMR), the Isovector Giant Dipole Resonance (IVGDR), the Gamow-Teller
Resonance (GTR), and the Spin-Dipole Resonance (SDR). The overall description
with the new functional is satisfactory and the tensor terms are shown to be
important particularly for the improvement of the Spin-Dipole Resonance
results. Predictions for the neutron skin thickness based on the non-energy
weighted sum rule of the Spin-Dipole Resonance are also given.Comment: 16 pages, 12 figure
Response function beyond mean field of neutron-rich nuclei
The damping of single-particle and collective motion in exotic isotopes is a
new topic and its study may shed light on basic problems of nuclear dynamics.
For instance, it is known that nuclear structure calculations are not able, as
a rule, to account completely for the empirical single-particle damping. In
this contribution, we present calculations of the single-particle self-energy
in the case of the neutron-rich light nucleus O, by taking proper care
of the continuum, and we show that there are important differences with the
case of nuclei along the valley of stability.Comment: 9 pages, 4 figures. To appear in: Proceedings of the Topical
Conference on Giant Resonances, Varenna, May 11-16, 1997 (Nucl. Phys. A, to
be published
Constraints on the symmetry energy and on neutron skins from the pygmy resonances in 68Ni and 132Sn
Correlations between the behavior of the nuclear symmetry energy, the neutron
skins, and the percentage of energy-weighted sum rule (EWSR) exhausted by the
Pygmy Dipole Resonance (PDR) in 68Ni and 132Sn have been investigated by using
different Random Phase Approximation (RPA) models for the dipole response,
based on a representative set of Skyrme effective forces plus meson-exchange
effective Lagrangians. A comparison with the experimental data has allowed us
to constrain the value of the derivative of the symmetry energy at saturation.
The neutron skin radius is deduced under this constraint.Comment: Accepted for publication in PRC Rapid Comminicatio
Regularization of zero-range effective interactions in finite nuclei
The problem of the divergences which arise in beyond mean-field calculations,
when a zero-range effective interaction is employed, has not been much
considered so far. Some of us have proposed, quite recently, a scheme to
regularize a zero-range Skyrme-type force when it is employed to calculate the
total energy, at second-order perturbation theory level, in uniform matter.
Although this scheme looked promising, the extension for finite nuclei is not
straightforward. We introduce such procedure in the current paper, by proposing
a regularization procedure that is similar, in spirit, to the one employed to
extract the so-called V_{\rm low-k} from the bare force. Although this has been
suggested already by B.G. Carlsson and collaborators, the novelty of our work
consists in setting on equal footing uniform matter and finite nuclei; in
particular, we show how the interactions that have been regularized in uniform
matter behave when they are used in a finite nucleus with the corresponding
cutoff. We also address the problem of the validity of the perturbative
approach in finite nuclei for the total energy.Comment: Accepted in Phys. Rev. C
(https://journals.aps.org/prc/accepted/4207aPfaIc313f02133c78b61b9c320e0a4e115d5
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