4,476 research outputs found
Ground-state properties and symmetry energy of neutron-rich and neutron-deficient Mg isotopes
A comprehensive study of various ground-state properties of neutron-rich and
neutron-deficient Mg isotopes with =20-36 is performed in the framework of
the self-consistent deformed Skyrme-Hartree-Fock plus BCS method. The
correlation between the skin thickness and the characteristics related with the
density dependence of the nuclear symmetry energy is investigated for this
isotopic chain following the theoretical approach based on the coherent density
fluctuation model and using the Brueckner energy-density functional. The
results of the calculations show that the behavior of the nuclear charge radii
and the nuclear symmetry energy in the Mg isotopic chain is closely related to
the nuclear deformation. We also study, within our theoretical scheme, the
emergence of an "island of inversion" at neutron-rich Mg nucleus, that
was recently proposed from the analyses of spectroscopic measurements of
Mg low-lying energy spectrum and the charge rms radii of all magnesium
isotopes in the shell.Comment: 13 pages, 13 figures, to be published in Physical Review
Structural transitions in vertically and horizontally coupled parabolic channels of Wigner crystals
Structural phase transitions in two vertically or horizontally coupled
channels of strongly interacting particles are investigated. The particles are
free to move in the -direction but are confined by a parabolic potential in
the -direction. They interact with each other through a screened power-law
potential (). In vertically coupled systems the channels
are stacked above each other in the direction perpendicular to the
-plane, while in horizontally coupled systems both channels are aligned
in the confinement direction. Using Monte Carlo (MC) simulations we obtain the
ground state configurations and the structural transitions as a function of the
linear particle density and the separation between the channels. At zero
temperature the vertically coupled system exhibits a rich phase diagram with
continuous and discontinuous transitions. On the other hand the vertically
coupled system exhibits only a very limited number of phase transitions due to
its symmetry. Further we calculated the normal modes for the Wigner crystals in
both cases. From MC simulations we found that in the case of vertically coupled
systems the zigzag transition is only possible for low densities. A
Ginzburg-Landau theory for the zigzag transition is presented, which predicts
correctly the behavior of this transition from which we interpret the
structural phase transition of the Wigner crystal through the reduction of the
Brillouin zone.Comment: 9 pages, 13 figure
Nuclear skin emergence in Skyrme deformed Hartree-Fock calculations
A study of the charge and matter densities and the corresponding rms radii
for even-even isotopes of Ni, Kr, and Sn has been performed in the framework of
deformed self-consistent mean field Skyrme HF+BCS method. The resulting charge
radii and neutron skin thicknesses of these nuclei are compared with available
experimental data, as well as with other theoretical predictions. The formation
of a neutron skin, which manifests itself in an excess of neutrons at distances
greater than the radius of the proton distribution, is analyzed in terms of
various definitions. Formation of a proton skin is shown to be unlikely. The
effects of deformation on the neutron skins in even-even deformed nuclei far
from the stability line are discussed.Comment: 16 pages, 17 figures, to be published in Physical Review
Temperature dependence of the volume and surface contributions to the nuclear symmetry energy within the coherent density fluctuation model
The temperature dependence of the volume and surface components of the
nuclear symmetry energy (NSE) and their ratio is investigated in the framework
of the local density approximation (LDA). The results of these quantities for
finite nuclei are obtained within the coherent density fluctuation model
(CDFM). The CDFM weight function is obtained using the temperature-dependent
proton and neutron densities calculated through the HFBTHO code that solves the
nuclear Skyrme-Hartree-Fock-Bogoliubov problem by using the cylindrical
transformed deformed harmonic-oscillator basis. We present and discuss the
values of the volume and surface contributions to the NSE and their ratio
obtained for the Ni, Sn, and Pb isotopic chains around double-magic Ni,
Sn, and Pb nuclei. The results for the -dependence of the
considered quantities are compared with estimations made previously for zero
temperature showing the behavior of the NSE components and their ratio, as well
as with the available experimental data. The sensitivity of the results on
various forms of the density dependence of the symmetry energy is studied. We
confirm the existence of `kinks' of these quantities as functions of the mass
number at MeV for the double closed-shell nuclei Ni and Sn
and the lack of `kinks' for the Pb isotopes, as well as the disappearance of
these kinks as the temperature increases.Comment: 14 pages, 12 figures, 1 table, accepted for publication in Physical
Review
Recovering coherence from decoherence: a method of quantum state reconstruction
We present a feasible scheme for reconstructing the quantum state of a field
prepared inside a lossy cavity. Quantum coherences are normally destroyed by
dissipation, but we show that at zero temperature we are able to retrieve
enough information about the initial state, making possible to recover its
Wigner function as well as other quasiprobabilities. We provide a numerical
simulation of a Schroedinger cat state reconstruction.Comment: 8 pages, in RevTeX, 4 figures, accepted for publication in Phys. Rev.
A (november 1999
Symmetry energy of deformed neutron-rich nuclei
The symmetry energy, the neutron pressure and the asymmetric compressibility
of deformed neutron-rich even-even nuclei are calculated on the examples of Kr
and Sm isotopes within the coherent density fluctuation model using the
symmetry energy as a function of density within the Brueckner energy-density
functional. The correlation between the thickness of the neutron skin and the
characteristics related with the density dependence of the nuclear symmetry
energy is investigated for isotopic chains of these nuclei in the framework of
the self-consistent Skyrme-Hartree-Fock plus BCS method. Results for an
extended chain of Pb isotopes are also presented. A remarkable difference is
found in the trend followed by the different isotopic chains: the studied
correlations reveal a smoother behavior in the Pb case than in the other cases.
We also notice that the neutron skin thickness obtained for Pb with
SLy4 force is found to be in a good agreement with recent data.Comment: 14 pages, 10 figures, 2 tables, accepted for publication in Physical
Review
Magnetic superelasticity and inverse magnetocaloric effect in Ni-Mn-In
Applying a magnetic field to a ferromagnetic NiMnIn
alloy in the martensitic state induces a structural phase transition to the
austenitic state. This is accompanied by a strain which recovers on removing
the magnetic field giving the system a magnetically superelastic character. A
further property of this alloy is that it also shows the inverse magnetocaloric
effect. The magnetic superelasticity and the inverse magnetocaloric effect in
Ni-Mn-In and their association with the first order structural transition is
studied by magnetization, strain, and neutron diffraction studies under
magnetic field.Comment: 6 pages, 8 figures. Published in the Physical Review
Magnetic superelasticity and inverse magnetocaloric effect in Ni-Mn-In
Applying a magnetic field to a ferromagnetic NiMnIn
alloy in the martensitic state induces a structural phase transition to the
austenitic state. This is accompanied by a strain which recovers on removing
the magnetic field giving the system a magnetically superelastic character. A
further property of this alloy is that it also shows the inverse magnetocaloric
effect. The magnetic superelasticity and the inverse magnetocaloric effect in
Ni-Mn-In and their association with the first order structural transition is
studied by magnetization, strain, and neutron diffraction studies under
magnetic field.Comment: 6 pages, 8 figures. Published in the Physical Review
A deformed QRPA formalism for single and two-neutrino double beta decay
We use a deformed QRPA formalism to describe simultaneously the energy
distributions of the single beta Gamow-Teller strength and the two-neutrino
double beta decay matrix elements. Calculations are performed in a series of
double beta decay partners with A = 48, 76, 82, 96, 100, 116, 128, 130, 136 and
150, using deformed Woods-Saxon potentials and deformed Skyrme Hartree-Fock
mean fields. The formalism includes a quasiparticle deformed basis and residual
spin-isospin forces in the particle-hole and particle-particle channels. We
discuss the sensitivity of the parent and daughter Gamow-Teller strength
distributions in single beta decay, as well as the sensitivity of the double
beta decay matrix elements to the deformed mean field and to the residual
interactions. Nuclear deformation is found to be a mechanism of suppression of
the two-neutrino double beta decay. The double beta decay matrix elements are
found to have maximum values for about equal deformations of parent and
daughter nuclei. They decrease rapidly when differences in deformations
increase. We remark the importance of a proper simultaneous description of both
double beta decay and single Gamow-Teller strength distributions. Finally, we
conclude that for further progress in the field it would be useful to improve
and complete the experimental information on the studied Gamow-Teller strengths
and nuclear deformations.Comment: 33 pages, 19 figures. To be published in Phys. Rev.
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