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  • 1990-1994  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 340 (1991), S. 111-117 
    ISSN: 1434-601X
    Keywords: 21.10.-k ; 21.60.-n ; 24.30.-v
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The centroid energy and the decay width of the giant monopole resonance in the unstable nucleus56Ni are predicted. The resulting 0+, ΔT=0 strength distribution, including the escape and the spreading width, displays a structure centered at around 18 MeV with the total width of about 5 MeV. We also study theM1 response in this nucleus which shows a strong isovector transition at 9.6 MeV and a weak isoscalar one at 7.5 MeV.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 339 (1991), S. 97-109 
    ISSN: 1434-601X
    Keywords: 21.60. Ev ; 21.60. Jz ; 27.70.+q
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract To clarify the physical nature of the orbital magnetic dipole excitations discussed widely in the past few years, a semiclassical model is presented and the nuclei156Gd and164Dy are investigated microscopically. The semi-classical model involves a consistent treatment of vibrational and rotational degrees of freedom; the microscopic results are obtained in quasiparticle-random-phase approximation (QRPA) with a realistic effective interaction. The results disagree with the picture of scissors modes or rotational vibrations.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 339 (1991), S. 383-389 
    ISSN: 1434-601X
    Keywords: 13.75.Gx ; 13.75.Jz ; 13.60.Hb
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract As stimulated by earlier attempts for obtaining theπNN andπNδ form factors from the deep inelastic lepton scattering data, we extend the analysis by taking into account effects of additional mesons includingρ, Ω, σ,K, andK *, with the coupling constants fixed by the lowenergy nucleon-nucleon and hyperon-nucleon scattering data. Contrary to an earlier claim that theπ NN andπNδ form factor must be very soft (e.g., with the cutoff mass less than 500 MeV in the monopole form), we find, for example, that with all form factors parametrized in the dipole form, a universal cutoff mass of 1150 MeV in theδ/N sector and 1400 MeV in theλ/σ sector yields predictions in excellent agreement with recently published neutrino data on the momentum fractions carried by thes, Ū, and¯d quarks, as well as consistent with the sea-to-valence ratio extracted from the CDHS data and the Femilab E615 experiment. Similar results can also be obtained by using exponential cutoffs for all couplings, or by using monopole forms for some vertices while retaining dipole forms for the rest. The success of the mesonexchange picture in generating the strangeness content in a proton suggests an alternative understanding of the origin of sea quarks in the proton.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Czechoslovak journal of physics 42 (1992), S. 1115-1135 
    ISSN: 1572-9486
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Hyperon-nucleon interaction models (A, B), which have been developed in the meson-exchange framework by the Jülich group, are reviewed, with some emphasis on characteristic conceptual differences compared to corresponding interactions constructed by the Nijmegen group. We report on two new versionsà and $$\tilde B$$ in which the explicit energydependence of the original models A and B is removed in order to simplify application in nuclear structure calculations. As a byproduct of our analysis we find that the resulting SU(3)-parameters likeF/(F+D) ratios do depend on the specific model used an on approximations applied. While all models provide a reasonable description of the scarce cross-section data, sizeable differences occur in the, so far unmeasured, spin observables, especially between our models and the Nijmegen soft-core model NSC. This demonstrates clearly that a measurement of such observables can easily discriminate between present models and thus shed some light on various aspects of the hyperon-nucleon interactions like e.g. the proper choice of parameter constraints. In addition, the results obtained with the energy-independent potentials (Ã, $$\tilde B$$ ) in a conventional first-order Brueckner calculation for a λ-hyperon in nuclear matter are presented. The binding energy B Λ (∞) of a λ-hyperon in nuclear matter was found to be 29.8 MeV (32.0 MeV) for model Ã( $$\tilde B$$ .
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 349 (1994), S. 59-64 
    ISSN: 1434-601X
    Keywords: 12.40.Aa ; 13.40.Fn
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The light-cone Fock-state decomposition of the nucleon involves pion-quark core (π′N′ andπ′Δ′) components. The size of the quark core is at present of special importance for the analysis of the onset of colour transparency in the A(e,e′p) reactions. With the light-coneNπ′N′ andNπ′Δ′ vertex functions deduced from experimental data on high-energy proton fragmentation into nucleons and isobars, we evaluate the effect of the pionic cloud on the electromagnetic form factors of nucleons. We find the quark core radius to be about 10% smaller than the nucleon's radius. Analysis of the renormalization of the total nucleon-nucleon cross section for the presence of the pionic cloud suggests a similar core radius.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 346 (1993), S. 253-260 
    ISSN: 1434-601X
    Keywords: 21.10.-k ; 21.60.-n ; 24.30.Cz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Within a microscopic approach which takes into account RPA configurations, the single-particle continuum and more complex 1p 1 h⊗phonon configurations isoscalar and isovector M1 excitations for the unstable nuclei56,78Ni and100,132Sn are calculated. For comparison, the experimentally known Ml excitations in40Ca and208Pb have also been calculated. In the latter nuclei good agreement in the centroid energy, the total transition strength and the resonance width is obtained. With the same parameters we predict the magnetic excitations for the unstable nuclei. The strength is sufficiently concentrated to be measurable in radioactive beam experiments. New features are found for the very neutron rich nucleus78Ni and the neutron deficient nucleus100Sn.
    Type of Medium: Electronic Resource
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