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  • 1990-1994  (13)
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  • 1
    Electronic Resource
    Electronic Resource
    Microscopic study of the low-energy3H(d, n)4He reaction (1991)
    Springer
    Few body systems 11 (1991), S. 137-142 
    Details
    ISSN: 1432-5411
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the3H(d, n)4He reaction at low energies within a multi-channel resonating-group calculation based on many-bodyn+α andd+3H configurations and pseudo-states as well as on an effective nucleonnucleon interaction containing central, spin-orbit, and tensor components. The low-energy fusion cross section is excellently reproduced within our approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01318558
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Nuclear effects on muon-catalyzed fusion in the (dtμ) system (1992)
    Springer
    Few body systems 13 (1992), S. 87-103 
    Details
    ISSN: 1432-5411
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have calculated the nuclear energy shifts and the nuclear decay widths of the molecular (dtμ) levels. While the muon is described within the Born-Oppenheimer approximation, we treat the nuclear degrees of freedom microscopically within the multi-channel resonating-group method based on many-bodyn+α andd+3H configurations and pseudo-states as well as on an effective nucleon-nucleon interaction containing central, spin-orbit, and tensor components. This microscopic nuclear model has been shown to reproduce the low-energy3H(d, n)4He fusion cross section and other properties of the 5-nucleon system very well. For nuclear separations larger than the range of the strong interaction and of the antisymmetrization our model reduces to the well-known 3-body Coulomb problem. For the (dtμ) ground state, which is of considerable interest for muoncatalyzed fusion, we calculate a nuclear energy shift and a decay width that agree quite well with previous estimates based on less flexible nuclear models. Our calculation seems to indicate that nuclear degrees of freedom other than the radial motion between the fragments are less important for the description of the properties of the molecular levels in the (dtμ) system. For the levels withL〉0 we obtain fusion rates that are noticeably smaller than those reported previously. Our in-flightd+(tμ)→n+(αμ), fusion rate agrees quite well with the results calculated by Bogdanova et al. based on a nuclear optical-model approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01103596
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Electromagnetic7Li form factors including meson-exchange contributions (1992)
    Springer
    Few body systems 13 (1992), S. 207-218 
    Details
    ISSN: 1432-5411
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the transversal and longitudinal form factors of the7Li ground-state doublet within a microscopic triton + α model allowing for specific distortion effects in the internal triton cluster. Meson-exchange contributions were taken into account in form of the dominant isovector pion- and rho-meson-exchange currents. For the derivation of the respective two-body operators we have used a consistent microscopic formalism developed by Riska which guarantees that the continuity equation is satisfied. The consideration of meson-exchange contributions brings our calculation in better agreement with the data. We find that only the longitudinal inelastic form factor has a diffraction minimum belowq≈4fm−1, in agreement with the data. Although our approach reproduces the low-q form factors qualitatively well, we underestimate the data at the higher momentum transfers noticeably. Finally we find that the isoscalar part of the central force gives the dominant contribution to the exchange currents while the tensor force plays only a minor role due to cancellation effects between the pion- and rho-meson-exchange contributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01080540
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  • 4
    Electronic Resource
    Electronic Resource
    Consistent microscopic study of the4He(e, e′d)d reaction (1992)
    Springer
    The European physical journal 342 (1992), S. 489-490 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the4He(e,e′d)d reaction within a consistent microscopic cluster model. Our calculation reproduces theQ 2-dependence of the Nikhef data, but overestimates its magnitude. A more detailed treatment of final state interactions seems to be important.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01294961
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Microscopic study of the low-energy3He(3He, 2p)4He and3H(3H, 2n)4He fusion cross sections (1991)
    Springer
    The European physical journal 339 (1991), S. 249-253 
    Details
    ISSN: 1434-601X
    Keywords: 25.10.+ s ; 25.55.e ; 25.55.Ek
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have calculated the3He(3He, 2p)4He and3H(3H, 2n)4He reaction cross sections at low energies within the microscopic multichannel resonating group method. For both reactions, we find good agreement with experiment. For the3H(3H, 2n)4He reaction, our calculated energy dependence reproduces that of each individual low-energy experimental data set, except for a normalization constant. Using this fact, we derive at a low-energy3H(3H, 2n)4He rate by taking the averaged mean of these fits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01284060
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  • 6
    Electronic Resource
    Electronic Resource
    Phase transition from a4He plasma to stable8Be matter (1991)
    Springer
    The European physical journal 339 (1991), S. 419-420 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We show that a4He quantum fluid will undergo a phase transition to stable8Be matter at densitiesρ ≈ 2×109109g/cm3. Our argumentation is qualitatively supported by an optimal hypernetted chain calculation of the helium fluid including nuclear forces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01560646
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical evidence for di-molecular rotational behaviour in the hypernuclei ∑ 8 Li and ∑ 8 Be (1991)
    Springer
    The European physical journal 339 (1991), S. 523-530 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01288436
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    The low-energyD(α, γ)6Li and6Li+208Pb→D+α+208Pb cross sections (1991)
    Springer
    The European physical journal 339 (1991), S. 335-339 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01560634
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    AstrophysicalS(E) factor of8Li (α,n 0)11B and inhomogeneous Big Bang nucleosynthesis (1990)
    Springer
    The European physical journal 337 (1990), S. 211-220 
    Details
    ISSN: 1434-601X
    Keywords: 24.30 ; 25.90
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The cross section of the11B(n, α)8Li reaction has been measured atE n=7.6 to 12.6 MeV. The neutron beam was produced via theD(d, n)3He reaction and aBF 3 counter (with naturalB isotopic composition) served both as target for the11B nuclides and as detector for the observation of the delayedα-activity of8Li. The data match well with previous results obtained atE n =12.5 to 20.0 MeV. Using the principle of detailed balance the data were converted to the case of the8Li(α, n 0)11B reaction. The associated astrophysicalS(E) factor is dominated by a resonance atE R=0.58 MeV of widthΓ R =200 keV, withS(E R )=8400 MeV b. ThisS (E R ) value for the n0 channel alone is already three times higher than the constantS(E) factor assumed previously and, thus, strengthens the significance of inhomogeneous Big Bang nucleosynthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01294294
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Pycnonuclear triple-alpha-fusion rate in hypernetted chain Approximation (1992)
    Springer
    The European physical journal 342 (1992), S. 133-140 
    Details
    ISSN: 1434-601X
    Keywords: 21.30 ; 67.20 ; 97.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the helium plasma in the hypernetted-chain-Approximation considering both short-ranged internuclear and long-ranged Coulomb interactions. The optimal two-particle wave function has been determined in HNC/0 approximation. The two-particle distribution functions, which have been calculated in various orders of HNC/n approximations (n=0, 4, 5), are used to determine the pycnonuclear triple-alpha-fusion rate in the density regime 108 g/cm3≤ρ≤1010 g/cm3, in which the fusing of three alpha-particles to form a12C-nucleus plays an important role in the crust evolution of an accreting old neutron star. Our calculation supports the idea that the helium liquid undergoes a phase transition to stable8Be matter at densities slightly lower thanρ≈3×109 g/ cm3 as the plasma induced screening potential then becomes strong enough to bind the8Be ground state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01288460
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    Paper (German National Licenses)
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