493 research outputs found
Deformed Hartree-Fock Calculation of Proton-Rich Nuclei
We perform Hartree-Fock+BCS calculations for even-even nuclei with 2 <= Z <=
82 and N ranging from outside the proton drip line to the experimental frontier
on the neutron-rich side. The ground state solutions are obtained for 737
nuclei, together with shape-coexistence solutions for 480 nuclei. Our method
features the Cartesian-mesh representation of single-particle wavefunctions,
which is advantageous in treating nucleon skins and exotic shapes. The results
are compared with those of the finite-range droplet model of Moller et al. as
well as the experimental values.Comment: 7 pages Latex, 5 postscript figures appended as uufil
Nuclear energy density functional from chiral pion-nucleon dynamics
We calculate the nuclear energy density functional relevant for N=Z even-even
nuclei in the systematic framework of chiral perturbation theory. The
calculation includes the one-pion exchange Fock diagram and the iterated
one-pion exchange Hartree and Fock diagrams. From these few leading order
contributions in the small momentum expansion one obtains already a very good
equation of state of isospin symmetric nuclear matter. We find that in the
region below nuclear matter saturation density the effective nucleon mass
deviates by at most 15% from its free space value ,
with for and
for higher densities. The parameterfree strength of
the -term, , is at saturation density
comparable to that of phenomenological Skyrme forces. The magnitude of
accompanying the squared spin-orbit density comes out
somewhat larger. The strength of the nuclear spin-orbit interaction,
, as given by iterated one-pion exchange is about half as large as
the corresponding empirical value, however, with the wrong negative sign. The
novel density dependencies of and
as predicted by our parameterfree calculation should be examined in nuclear
structure calculations (after introducing an additional short range spin-orbit
contribution constant in density).Comment: 16 pages, 5 figure
Nuclear energy density functional from chiral pion-nucleon dynamics: Isovector spin-orbit terms
We extend a recent calculation of the nuclear energy density functional in
the systematic framework of chiral perturbation theory by computing the
isovector spin-orbit terms: . The calculation
includes the one-pion exchange Fock diagram and the iterated one-pion exchange
Hartree and Fock diagrams. From these few leading order contributions in the
small momentum expansion one obtains already a good equation of state of
isospin-symmetric nuclear matter. We find that the parameterfree results for
the (density-dependent) strength functions and agree
fairly well with that of phenomenological Skyrme forces for densities . At very low densities a strong variation of the strength functions
and with density sets in. This has to do with chiral
singularities and the presence of two competing small mass scales
and . The novel density dependencies of and
as predicted by our parameterfree (leading order) calculation should
be examined in nuclear structure calculations.Comment: 9 pages, 3 figure, published in: Physical Review C68, 014323 (2003
Cross sections for the excitation of isovector charge-exchange resonances in 208Tl
The Glauber approximation for the treatment of heavy-ion scattering, has
already been shown to give reliable predictions for the reaction cross section
in the particular case of intermediate energy charge-exchange processes. In the
present work, we couple a Glauber-type model to microscopic Random Phase
Approximation calculations of the charge-exchange excitations of Pb.
The aim is to solve the longstanding question whether the very elusive
charge-exchange isovector monopole has been really identified in the past
experiments, or other multipoles were prevalent in the observed spectra.Comment: text + 4 figures; accepted for publication in Phys. Rev.
Widths of Isobaric Analog Resonances: a microscopic approach
A self-consistent particle-phonon coupling model is used to investigate the
properties of the isobaric analog resonance in Bi. It is shown that
quantitative agreement with experimental data for the energy and the width can
be obtained if the effects of isospin-breaking nuclear forces are included, in
addition to the Coulomb force effects. A connection between microscopic model
predictions and doorway state approaches which make use of the isovector
monopole resonance, is established via a phenomenological ansatz for the
optical potential.Comment: 18 pages, 1 figure. To appear on Phys. Rev. C (tentatively scheduled
for June 1998
Chiral approach to nuclear matter: Role of explicit short-range NN-terms
We extend a recent chiral approach to nuclear matter by including the most
general (momentum-independent) NN-contact interaction. Iterating this
two-parameter contact-vertex with itself and with one-pion exchange the
emerging energy per particle exhausts all terms possible up-to-and-including
fourth order in the small momentum expansion. The equation of state of pure
neutron matter, , can be reproduced very well up to quite high
neutron densities of \rho_n=0.5\fmd by adjusting the strength of a repulsive
-contact interaction. Binding and saturation of isospin-symmetric nuclear
matter is a generic feature of our perturbative calculation. Fixing the maximum
binding energy per particle to MeV we find that any
possible equilibrium density lies below \rho_0^{\rm max}=0.191\fmd.
The additional constraint from the neutron matter equation of state leads
however to a somewhat too low saturation density of \rho_0 =0.134 \fmd. We
also investigate the effects of the NN-contact interaction on the complex
single-particle potential . We find that the effective
nucleon mass at the Fermi-surface is bounded from below by . This property keeps the critical temperature of the liquid-gas phase
transition at somewhat too high values MeV. The downward bending
of the asymmetry energy above nuclear matter saturation density is a
generic feature of the approximation to fourth order. Altogether, there is
within this complete fourth-order calculation no "magic" set of adjustable
short-range parameters with which one could reproduce simultaneously and
accurately all semi-empirical properties of nuclear matter.Comment: 24 pages, 12 figures, accepted for publication in: Eur. Phys. J.
Superdeformed bands in neutron-rich Sulfur isotopes suggested by cranked Skyrme-Hartree-Fock calculations
On the basis of the cranked Skyrme-Hartree-Fock calculations in the
three-dimensional coordinate-mesh representation, we suggest that, in addition
to the well-known candidate 32S, the neutron-rich nucleus 36S and the drip-line
nuclei,48S and 50S, are also good candidates for finding superdeformed
rotational bands in Sulfur isotopes. Calculated density distributions for the
superdeformed states in 48S and 50S exhibit superdeformed neutron skinsComment: 18 pages including 10 ps figure
Escape and Spreading Properties of Charge-Exchange Resonances in Bi 208
The properties of charge-exchange excitations of Pb with , i.e., the isobaric analog and Gamow-Teller resonances, are studied within
a self-consistent model making use of an effective force of the Skyrme type.
The well-known isobaric analog case is used to assess the reliability of the
model. The calculated properties of the Gamow-Teller resonance are compared
with recent experimental measurements with the aim of better understanding the
microscopic structure of this mode.Comment: 26 pages including references, figure captions and tables. Figures
are available upon request at [email protected] (decnet 32858::COLO).
Preprint code: IPNO/TH 94-2
Spin-orbit interaction in Hartree-Fock calculations
The contribution of the spin-orbit interaction in Hartree-Fock calculations
for closed shell nuclei is studied. We obtain explicit expressions for the
finite range spin-orbit force. New terms with respect to the traditional
spin-orbit expressions are found. The importance of the finite-range is
analyzed. Results obtained with spin-orbit terms taken from realistic
interactions are presented. The effect of the spin-orbit isospin dependent
terms is evaluated.Comment: To be published on Nuovo Cimento
Resonant continuum in the Hartree-Fock+BCS approximation
A method for incorporating the effect of the resonant continuum into
Hartree-Fock+BCS equations is proposed. The method is applied for the case of
a neutron-rich nucleus calculated with a Skyrme-type force plus a zero-range
pairing interaction and the results are compared with
Hartree-Fock-Bogoliubov calculations. It is shown that the widths of resonant
states have an important effect on the pairing properties of nuclei close to
the drip line.Comment: 9 pages, 2 figures, comparison with HFB adde
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