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  • 21.60.Gx  (6)
  • 1
    ISSN: 1434-601X
    Keywords: 25.55.-e ; 25.70.Jj ; 21.60.Gx
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The two presently available measurements of the low-energy3H(α, γ)7Li reaction differ from each other by roughly 30% in total magnitude as well as in their determination of the branching ratios for the transition into the two final7Li bound states. Studying the3H(α, γ)7Li reaction in the framework of the microscopic Resonating Group Method we were able to reproduce both experimental total cross sections using different effective nucleon-nucleon interactions. However, none of the effective forces yields branching ratios compatible with the data measured by the Toronto-Münster-collaboration.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 334 (1989), S. 1-9 
    ISSN: 1434-601X
    Keywords: 21.60.Cs ; 21.60.Gx ; 23.20.-G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract StrongB(E1) transitions have been recently observed between states in the18O nucleus which follow roughly the energy sequence of a dimolecular α+14C rotator. These findings have been interpreted by Gai et al. as evidence for a molecular dipole degree of freedom being present in the18O nucleus. However, this idea was contradicted by the results of a microscopic multichannel calculation performed by Descouvemont and Baye which was based on elastic α+14C and inelastic α+14C(2+) many-body cluster wave functions. We have improved this study by performing a microscopic multichannel calculation including additionally an+17O many-body fragmentation in order to enlarge our model space by those shell model components which dominate the structure of the (positive parity)18O ground state band. Like Descouvemont and Baye we find a positive parity α+14C molecular band in18O and, additionally, a rather strong collectivity in the lowest 1−, 3− and 5− states in18O. However, since the internal structure is different within these states, the calculated states should not be interpreted as a negative parity α+14C molecular band. In this perspective, the microscopic multichannel calculations do not support the hypothesis of a molecular dipole degree of freedom being present in the18O nucleus.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 333 (1989), S. 219-227 
    ISSN: 1434-601X
    Keywords: 21.60.Gx ; 25.55.-e ; 24.10.Eq
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have performed a microscopic study of the3He(d,p) α reaction at astrophysical energies within the framework of the Resonating Group Method adopting three different effective nucleon-nucleon interactions. The calculations suggest that the low-energy3He(d,p) α cross section is in good approximation given by the contribution arising from the 3/2+ resonant state atE R =245 keV. In fact, the low-energy data can be better (and more physically) described by a single Breit-Wigner resonance parametrization than by a polynomial fit. Our fit to the3He(d,p) α cross section results in a noticeable reduction in the uncertainties of the resonance parameters of the 3/2+ resonant state as well as in a significantly improved extrapolation of the data to astrophysically important energies. On the basis of this extrapolation we were able to quantitatively deduce the enhancement of the low-energy cross section due to electron screening effects from the data of Krauss et al. and Engstler et al. These experimental enhancement factors were compared with various theoretical models which are all based on the Born-Oppenheimer approximation. As the models underestimate the observed enhancement we suggest that the theoretical study of electron screening effects requires a dynamical treatment.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 334 (1989), S. 221-230 
    ISSN: 1434-601X
    Keywords: 21.80.+a ; 21.40.+d ; 21.60.Gx
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the particle-bound levels in the hypernucleiΛ 3,4H,Λ 5He,Λ 8Li andΛ 8,9Be in the framework of the full microscopic Resonating Group Method (RGM). In a first step we have solved the respective nuclear many-body problem within the RGM. For each hypernucleus we have then performed a static calculation, in which the nuclear degrees of freedom were kept fixed, and a dynamical calculation in which nuclear degrees of freedom were allowed to vary. The differences between these two studies allowed us to investigate nuclear distortion effects caused by the presence of theΛ-particle. We find the nuclear distortion effects to be inverse proportional to the binding of the nuclear constituents. Thus, the strongest effects are observed forΛ 3H and forΛ 9Be. Our dynamical approach does not show the strong overbinding ofΛ 3H andΛ 9Be as reported in other cluster model studies. Our results for thep-shell hypernuclei agree reasonably well with those obtained in a semi-microscopic Orthogonal Condition Model (OCM) study which used the same effectiveΛN-interaction as employed in our calculation.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 339 (1991), S. 335-339 
    ISSN: 1434-601X
    Keywords: 21.60.Gx ; 23.20.−g ; 25.55.−e
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have calculated theE1 andE2 contributions to the low-energyD(α,γ)6Li fusion and to the6Li+208Pb →D+α+208Pb Coulomb dissociation cross sections within a multichannel Resonating Group calculation based on many-body deuteron+α configurations and pseudo-states. For both reactions experimentally determined cross sections are reasonably well reproduced. We find that dipole capture contributes noticeably to the fusion cross sections atE≦500 keV, while it is negligible in the Coulomb dissociation data.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 339 (1991), S. 523-530 
    ISSN: 1434-601X
    Keywords: 21.80.+a ; 21.60.Gx
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have performed microscopic cluster studies of light∑-hypernuclei based on effective nucleon-nucleon and two different sigma-nucleon interactions. Our calculation confirms a bound 0+ state in ∑ 4 He and ∑ 4 H, but reveals no evidence for levels in other partial waves. We have investigated the ∑ 8 Li and ∑ 8 Be hypernuclei in a microscopic 3-cluster approach. For both hypernuclei, our calculation shows that the lowest levels in the partial wavesJ=0–4 are bound or quasibound states of collective nature and show a strong α ∑ 4 H and α + ∑ 4 He clustering. These levels form a sequence of states which can be well interpreted as arising from a rotatingα+ ∑ 4 H orα+ ∑ 4 He di-molecule. Our results are compared to those of similar studies for lightΛ-hypernuclei which do not show evidence for this kind of collective degrees of freedom.
    Type of Medium: Electronic Resource
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