126 research outputs found
On the nuclear symmetry energy and the neutron skin in neutron-rich nuclei
The symmetry energy for nuclear matter and its relation to the neutron skin
in finite nuclei is discussed. The symmetry energy as a function of density
obtained in a self-consistent Green function approach is presented and compared
to the results of other recent theoretical approaches. A partial explanation of
the linear relation between the symmetry energy and the neutron skin is
proposed. The potential of several experimental methods to extract the neutron
skin is examined.Comment: to appear in Phys. Rev.
Center-of-mass effects on the quasi-hole spectroscopic factors in the 16O(e,e'p) reaction
The spectroscopic factors for the low-lying quasi-hole states observed in the
16O(e,e'p)15N reaction are reinvestigated with a variational Monte Carlo
calculation for the structure of the initial and final nucleus. A computational
error in a previous report is rectified. It is shown that a proper treatment of
center-of-mass motion does not lead to a reduction of the spectroscopic factor
for -shell quasi-hole states, but rather to a 7% enhancement. This is in
agreement with analytical results obtained in the harmonic oscillator model.
The center-of-mass effect worsens the discrepancy between present theoretical
models and the experimentally observed single-particle strength. We discuss the
present status of this problem, including some other mechanisms that may be
relevant in this respect.Comment: 14 pages, no figures, uses Revtex, to be published in Phys. Rev. C 58
(1998
Electromagnetic interaction in chiral quantum hadrodynamics and decay of vector and axial-vector mesons
The chiral invariant QHD-III model of Serot and Walecka is applied in the calculation of some meson properties. The electromagnetic interaction is included by extending the symmetry of the model to the local U(1) \times SU(2)_{R} \times SU(2)_{L} group. The minimal and nonminimal contributions to the electromagnetic Lagrangian are obtained in a new representation of QHD-III. Strong decays of the axial-vector meson, a_{1} \to \pi \rho, a_{1} \to \pi \sigma, and the electromagnetic decays \rho \to \pi \pi \gamma, a_{1} \to \pi \gamma and \rho \to \pi \gamma are calculated. The low-energy parameters for the \pi-\pi scattering are calculated in the tree-level approximation. The effect of the auxiliary Higgs bosons, introduced in QHD-III in order to generate masses of the vector and axial-vector mesons via the Higgs mechanism, is studied as well. This is done on the tree level for \pi-\pi scattering and on the level of one-loop diagrams for the a_{1} \to \pi \gamma decay. It is demonstrated that the model successfully describes some features of meson phenomenology in the non-strange sector
Long-range correlations in finite nuclei: comparison of two self-consistent treatments
Long-range correlations, which are partially responsible for the observed fragmentation and depletion of low-lying single-particle strength, are studied in the Green's function formalism. The self-energy is expanded up to second order in the residual interaction. We compare two methods of implementing self-consistency in the solution of the Dyson equation beyond Hartree-Fock, for the case of the 16O nucleus. It is found that the energy-bin method and the BAGEL method lead to globally equivalent results. In both methods the final single-particle strength functions are characterized by exponential tails at energies far from the Fermi level
Determination of the nature of the Cu coordination complexes formed in the presence of NO and NH3 within SSZ-13
Ammonia-selective catalytic reduction (NH3-SCR) using Cu zeolites is a well-established strategy for the abatement of NOx gases. Recent studies have demonstrated that Cu is particularly active when exchanged into the SSZ-13 zeolite, and its location in either the 6r or 8r renders it an excellent model system for fundamental studies. In this work, we examine the interaction of NH3-SCR relevant gases (NO and NH3) with the Cu2+ centers within the SSZ-13 structure, coupling powder diffraction (PD), X-ray absorption spectroscopy (XAFS), and density functional theory (DFT). This combined approach revealed that, upon calcination, cooling and gas exposure Cu ions tend to locate in the 8r window. After NO introduction, Cu-ions are seen to coordinate to two framework oxygens and one NO molecule, resulting in a bent Cu-nitrosyl complex with a Cu-N-O bond angle of similar to 150 degrees. Whilst Cu seems to be partially reduced/changed in coordination state, NO is partially oxidized. On exposure to NH3 while the PD data suggest the Cu2+ ion occupies a similar position, simulation and XAFS pointed toward the formation of a Jahn-Teller distorted hexaamine complex [Cu(NH3)(6)](2+) in the center of the cha cage. These results have important implications in terms of uptake and storage of these reactive gases and potentially for the mechanisms involved in the NH3-SCR process
Production of e+e- pairs in proton-deuteron capture to 3He
The process p+d \leftrightarrow 3He + \gamma* at intermediate energies is
described using a covariant and gauge-invariant model, and a realistic pd3He
vertex. Both photodisintegration of 3He and proton-deuteron capture with
production of e+e- pairs are studied, and results for cross sections and
response functions are presented. The effect of time-like formfactors on the
dilepton cross sections is investigated as well.Comment: 10 pages, 4 figures, Revtex, to be published in Physics Letters
Quasiparticle properties in a density functional framework
We propose a framework to construct the ground-state energy and density
matrix of an N-electron system by solving selfconsistently a set of
single-particle equations. The method can be viewed as a non-trivial extension
of the Kohn-Sham scheme (which is embedded as a special case). It is based on
separating the Green's function into a quasi-particle part and a background
part, and expressing only the background part as a functional of the density
matrix. The calculated single-particle energies and wave functions have a clear
physical interpretation as quasiparticle energies and orbitals.Comment: 12 pages, 1 figure, to be published in Phys. Rev.
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