2,750 research outputs found
Reaction cross sections for proton scattering from stable and unstable nuclei based on a microscopic approach
Microscopic optical model potential results for reaction cross sections of
proton elastic scattering are presented. The applications cover the 10-1000 MeV
energy range and consider both stable and unstable nuclei. The study is based
on in-medium g-matrix full-folding optical model approach with the appropriate
relativistic kinematic corrections needed for the higher energy applications.
The effective interactions are based on realistic NN potentials supplemented
with a separable non-Hermitian term to allow optimum agreement with current NN
phase-shift analyzes, particularly the inelasticities above pion production
threshold. The target ground-state densities are obtained from
Hartree-Fock-Bogoliubov calculations based on the finite range, density
dependent Gogny force. The evaluated reaction cross sections for proton
scattering are compared with measurements and their systematics is analyzed. A
simple function of the total cross sections in terms of the atomic mass number
is observed at high energies. At low energies, however, discrepancies with the
available data are observed, being more pronounced in the lighter systems.Comment: 11 pages, 4 figures, submitted to Phys. Rev.
Microscopic analysis of K^+-nucleus elastic scattering based on K^+N phase shifts
We investigate -nucleus elastic scattering at intermediate energies
within a microscopic optical model approach. To this effect we use the current
-nucleon {\it (KN)} phase shifts from the Center for Nuclear Studies of
the George Washington University as primary input. First, the {\it KN} phase
shifts are used to generate Gel'fand-Levitan-Marchenko real and local inversion
potentials. Secondly, these potentials are supplemented with a short range
complex separable term in such a way that the corresponding unitary and
non-unitary {\it KN} matrices are exactly reproduced. These {\it KN}
potentials allow to calculate all needed on- and off-shell contributions of the
matrix,the driving effective interaction in the full-folding
-nucleus optical model potentials reported here. Elastic scattering of
positive kaons from Li, C, Si and Ca are studied at
beam momenta in the range 400-1000 MeV/{}, leading to a fair description of
most differential and total cross section data. To complete the analysis the
full-folding model, three kinds of simpler calculations are considered
and results discussed. We conclude that conventional medium effects, in
conjunction with a proper representation of the basic {\it KN} interaction are
essential for the description of -nucleus phenomena.Comment: 11 pages, 1 table, 12 figures, submitted to PR
An in-medium full-folding model approach to quasielastic (p,n) charge-exchange reactions
A microscopic description of the quasielastic (p,n) charge-exchange reaction
(here, charge-exchange scattering between analogue states) is presented and
discussed. Emphasis is focused on the spin-isospin structure of the
projectile-target coupling. The model is a coupled-channel extension of the
full-folding optical model approach (OMP) developed for nucleon elastic
scattering, where emphasis is placed on retaining the genuine off-shell
behavior of realistic effective interactions in the nuclear medium. The
resulting non-local optical potentials are applied to the calculation of (p,n)
differential cross sections, with particular emphasis on small-angle Fermi
() cross-sections to isobaric analog states. These parameter-free
results provide a reasonable description of the C(p,n)-data at proton
energies above 100 MeV, but deteriorate for heavier targets. These
shortcomings are analyzed and possible ways to correct them are discussed.Comment: 20 pages plus 10 figures. Accepted for publication in Phys. Rev.
Nuclear halo structure from quasielastic charge-exchange reactions
Neutron and proton densities in the nuclear periphery are investigated within
(p,n) charge-exchange isobar transitions. For this purpose we have developed
parameter-free optical potentials with a detailed treatment of the in-medium
part of the effective interaction. Non local coupled-channel Lane
equations are solved to obtain the scattering observables. The use of
conventional proton and neutron densities significantly underestimates Fermi
(forward-angle) cross-sections in agreement with findings by various other
groups. However, we have found model-independent densities which provide a
remarkable improvement in the description of the quasielastic scattering
data.The densities obtained are consistent with recent measurements at CERN in
studies of the neutron-to-proton halo factor f(r)=Z with
antiprotons. These findings provide an alternative way to investigate the
nuclear periphery, and may also help to solve the long-standing puzzle of the
underestimated Fermi cross section in (p,n) charge-exchange phenomena.Comment: 5 pages and 2 figs. Presented at the Baryons-04 Conference
(Palaiseau, France, Oct 2004). To appear in Nucl. Phys.
Sensitivity of nucleon-nucleus scattering to the off-shell behavior of on-shell equivalent NN potentials
The sensitivity of nucleon-nucleus elastic scattering to the off-shell
behavior of realistic nucleon-nucleon interactions is investigated when
on-shell equivalent nucleon-nucleon potentials are used. The study is based on
applications of the full-folding optical model potential for an explicit
treatment of the off-shell behavior of the nucleon-nucleon effective
interaction. Applications were made at beam energies between 40 and 500 MeV for
proton scattering from 40Ca and 208Pb. We use the momentum-dependent Paris
potential and its local on-shell equivalent as obtained with the
Gelfand-Levitan and Marchenko inversion formalism for the two nucleon
Schroedinger equation. Full-folding calculations for nucleon-nucleus scattering
show small fluctuations in the corresponding observables. This implies that
off-shell features of the NN interaction cannot be unambiguously identified
with these processes. Inversion potentials were also constructed directly from
NN phase-shift data (SM94) in the 0-1.3 GeV energy range. Their use in
proton-nucleus scattering above 200 MeV provide a superior description of the
observables relative to those obtained from current realistic NN potentials.
Limitations and scope of our findings are presented and discussed.Comment: 17 pages tightened REVTeX, 8 .ps figures, submitted to Phys. Rev.
Functional medium-dependence of the nonrelativistic optical model potential
By examining the structure in momentum and coordinate space of a two-body
interaction spherically symmetric in its local coordinate, we demonstrate that
it can be disentangled into two distinctive contributions. One of them is a
medium-independent and momentum-conserving term, whereas the other is
functionally --and exclusively-- proportional to the radial derivative of the
reduced matrix element. As example, this exact result was applied to the
unabridged optical potential in momentum space, leading to an explicit
separation between the medium-free and medium-dependent contributions. The
latter does not depend on the strength of the reduced effective interaction but
only on its variations with respect to the density. The modulation of radial
derivatives of the density enhances the effect in the surface and suppresses it
in the saturated volume. The generality of this result may prove to be useful
for the study of surface-sensitive phenomena.Comment: 11 pages, 5 figures, submitted to Phys. Rev.
Surface-peaked medium sensitivity of the optical potential: an exact result
Microscopic optical model potentials for elastic hadron-nucleus scattering usually take the form of a convolution of a two-body effective interaction with the target ground-state mixed density. Within the Brueckner-Bethe-Goldstone gmatrix approach for the effective interaction, nuclear medium effects are made explicit by means spatial integrals throughout the bulk of the nucleus. In this contribution we discuss a novel and exact approach to track down the manifestation of intrinsic nuclear medium effects. After examining the momentumand coordinate-space structure of a two-body effective interaction âspherically symmetric in its mean coordinateâ it is demonstrated that the intrinsic medium effects in the optical potential depend solely on the gradient of a reduced interaction. This feature implies the confinement of intrinsic medium effects to regions where the density varies most, i.e. the nuclear surface. This finding may be of special significance in the study of nuclear collisions sensitive to the peripheric structure of nuclei. We illustrate some of its implications in the context of 10Be + p elastic scattering at 39.1A MeV
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