142 research outputs found
Electromagnetic Dissociation as a Tool for Nuclear Structure and Astrophysics
Coulomb dissociation is an especially simple and important reaction
mechanism. Since the perturbation due to the electric field of the nucleus is
exactly known, firm conclusions can be drawn from such measurements.
Electromagnetic matrix elements and astrophysical S-factors for radiative
capture processes can be extracted from experiments. We describe the basic
theory, new results concerning higher order effects in the dissociation of
neutron halo nuclei, and briefly review the experimental results obtained up to
now. Some new applications of Coulomb dissociation for nuclear astrophysics and
nuclear structure physics are discussed.Comment: 10 pages, 1 figure, to appear in Proceedings of the International
School on Nuclear Physics; 22nd Course: ``Radioactive Beams for Nuclear and
Astro Physics'', Erice/Sicily/Italy, September 16 - 24, 200
The High-Density Symmetry Energy in Heavy-Ion Collisions and Compact Stars
High-density nuclear symmetry energy is of crucial importance in astrophysics. Information on such energy has been obtained from mass-radius determinations of neutron stars (NSs), and in the future NS mergers will increasingly contribute. In the laboratory, the symmetry energy can be studied in heavy-ion collisions (HICs) at different incident energies over a large range, from very low to several times higher saturation density. Transport theory is necessary to extract the symmetry energy from the typically non-equilibrated nuclear collisions. In this contribution, we first review the transport approaches, their differences, and recent studies of their reliability. We then discuss several prominent observables, which have been used to determine the symmetry energy at high density: collective flow, light cluster emission, and particle production. It is finally argued that the results of the symmetry energy from microscopic many-body calculations, nuclear structure, nuclear reactions, and astrophysics begin to converge but still need considerable improvements in terms of accuracy
Indexed and Fibred Structures for Hoare Logic
Indexed and fibred categorical concepts are widely used in computer science as models of logical systems and type theories. Here we focus on Hoare logic and show that a comprehensive categorical analysis of its axiomatic semantics needs the languages of indexed category and fibred category theory. The structural features of the language are presented in an indexed setting, while the logical features of deduction are modeled in the fibred one. Especially, Hoare triples arise naturally as special arrows in a fibred category over a syntactic category of programs, while deduction in the Hoare calculus can be characterized categorically by the heuristic deduction = generation of cartesian arrows + composition of arrows.publishedVersio
Nuclear stopping and flow in heavy ion collisions and the in-medium NN cross section
We present transport calculations for heavy ion reactions in which the mean
field and the in-medium nucleon-nucleon cross section are consistently based on
the same effective interaction, i.e. the in-medium T-matrix from microscopic
Dirac-Brueckner calculations. Doing so, the stopping in central reactions in
terms of the recently proposed observable and the correlation to
the behavior of the directed flow is investigated. The relation to the nuclear
shear viscosity is discussed.Comment: 9 pages, 4 figure
Asymmetric Colliding Nuclear Matter Approach in Heavy Ion Collisions
The early stage of a heavy ion collision is governed by local non-equilibrium
momentum distributions which have been approximated by colliding nuclear matter
configurations, i.e. by two Lorentz elongated Fermi ellipsoids. This approach
has been extended from the previous assumption of symmetric systems to
asymmetric 2-Fermi sphere configurations, i.e. to different densities. This
provides a smoother transition from the limiting situation of two
interpenetrating currents to an equilibrated system. The model is applied to
the dynamical situations of heavy ion collisions at intermediate energies
within the framework of relativistic transport (RBUU) calculations. We find
that the extended colliding nuclear matter approach is more appropriate to
describe collective reaction dynamics in terms of flow observables, in
particular, for the elliptic flow at low energies.Comment: 21 pages, 8 figures, accepted for publication in Nuclear Physics
Stopping and Isospin Equilibration in Heavy Ion Collisions
We investigate the density behaviour of the symmetry energy with respect to
isospin equilibration in the combined systems at relativistic
energies of 0.4 and . The study is performed within a relativistic
framework and the contribution of the iso-vector, scalar field to the
symmetry energy and the isospin dynamics is particularly explored. We find that
the isospin mixing depends on the symmetry energy and a stiff behaviour leads
to more transparency. The results are also nicely sensitive to the "fine
structure" of the symmetry energy, i.e. to the covariant properties of the
isovector meson fields. The isospin tracing appears much less dependent on the
in-medium neutron-proton cross-sections () and this makes such
observable very peculiar for the study of the isovector part of the nuclear
equation of state. Within such a framework, comparisons with experiments
support the introduction of the meson in the description of the
iso-vector equation of state.Comment: 11 pages, 5 figures. Accepted for publication in Phys.Lett.
Dirac-Brueckner Hartree-Fock Approach: from Infinite Matter to Effective Lagrangians for Finite Systems
One of the open problems in nuclear structure is how to predict properties of
finite nuclei from the knowledge of a bare nucleon-nucleon interaction of the
meson-exchange type. We point out that a promising starting point consists in
Dirac-Brueckner-Hartree-Fock (DBHF) calculations us- ing realistic
nucleon-nucleon interactions like the Bonn potentials, which are able to
reproduce satisfactorily the properties of symmetric nuclear matter without the
need for 3-body forces, as is necessary in non-relativistic BHF calculations.
However, the DBHF formalism is still too com- plicated to be used directly for
finite nuclei. We argue that a possible route is to define effective
Lagrangians with density-dependent nucleon-meson coupling vertices, which can
be used in the Relativistic Hartree (or Relativistic Mean Field (RMF)) or
preferrably in the Relativistic Hartree- Fock (RHF) approach. The
density-dependence is matched to the nuclear matter DBHF results. We review the
present status of nuclear matter DBHF calculations and discuss the various
schemes to construct the self-energy, which lead to differences in the
predictions. We also discuss how effective Lagrangians have been constructed
and are used in actual calculations. We point out that completely consistent
calculations in this scheme still have to be performed.Comment: 16 pages, to be published in Journal of Physics G: Nuclear and
Particle Physics, special issue
Isospin Effects on Strangeness in Heavy-Ion Collisions
Kaon properties are studied within the framework of a fully covariant
transport approach. The kaon-nucleon potential is evaluated in two schemes, a
chiral perturbative approach and an effective One-Boson-Exchange model. Isospin
effects are explicitly accounted for in both models. The transport calculations
indicate a significant sensitivity of momentum distributions and total yields
of isospin states on the choice of the kaon-nucleon interaction.
Furthermore, isospin effects are rather moderate on absolute kaon yields, but
appear on strangeness ratios. This is an important issue in determining the
high density symmetry energy from studies of strangeness production in
heavy-ion collisions.Comment: 15 papes, 5 figures. Accepted for publication in Nuclear Physic
Heavy Ion Fragmentation Reactions at Energies of 35-140 MeV in a Combined Transport and Statistical Approach
Fragment formation in heavy ion collisions at low to intermediate energy is described by a combined application of transport theory of the Boltzmann type and of a statistical program for the decay of the fragments at the late stage. The transport equations are solved by simulations using the test particle method as a finite element representation of the phase space distribution. The description of experimental data is reasonable overall, but the fragment velocity distributions point to the presence of other mechanisms and the role of fluctuations
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