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  • 24.30.−v  (2)
  • 25.40  (2)
  • 97.10  (2)
  • 24.10.Eq  (1)
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  • 1
    Digitale Medien
    Digitale Medien
    New22Ne(α,n)25Mg-resonances at very low energies relevant for the astrophysical s-process (1991)
    Springer
    The European physical journal 338 (1991), S. 367-368 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 25.55 ; 97.10
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The 22Ne(α,n)25Mgreaction is thought to be one of the main neutron sources for the astrophysical s-process. Thus cross section data for this reaction have been obtained from near the threshold (E α≈570keV) up toE α=2100 keV using the 4 MV DYNAMITRON accelerator at Stuttgart, the windowless gastarget system RHINOCEROS and a 4π neutron detector. Two new resonances have been observed atE α=623 ± 6 and 838 ± 6 kev, which dominate the reaction rate at T9〈0.3.Possible background reactions are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01288203
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  • 2
    Digitale Medien
    Digitale Medien
    Helium burning of22Ne (1989)
    Springer
    The European physical journal 334 (1989), S. 491-510 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 25.55 ; 97.10
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The22Ne(α, γ)26Mg and22Ne(α, n)25Mg reactions were investigated forE α(lab) from 0.71 to 2.25 MeV. Neon gas enriched to 99% in22Ne was recirculated in a differentially pumped gas target system of the extended type. Theγ-ray transitions were observed with Ge(Li) detectors and the neutrons with3He ionization chambers. A previously known resonance at ER(lab)=2.05 MeV was verified and 15 new resonances were found in the energy range covered, with the lowest at ER(lab)=0.83 MeV. Information on resonance energies, widths, strengths,γ-ray branching ratios, as well asJ π assignments, is reported. The energy range investigated corresponds to the important temperature range ofT 9 from 0.3 to 1.4 (109 K), for which the astrophysical rates were determined for both reactions. The results show that the ratios of the rates for22Ne(α, n)25Mg and22Ne(α, γ)26Mg are significantly smaller than the previously adopted values, e.g., by at least a factor of 60 nearT 9=0.65. Thus, the22Ne(α, n)25Mg reaction will likely play a smaller role as a neutron source fors-process nucleosynthesis, than has frequently been assumed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01294757
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  • 3
    Digitale Medien
    Digitale Medien
    Low energy resonances in21Ne(p,γ)22Na examined with a high energy resolution ion beam (1992)
    Springer
    The European physical journal 343 (1992), S. 361-366 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 24.30.−v
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract TheE R=126, 272 and 291 keV resonances in the21Ne(p, γ)22Na reaction have been investigated with a high-energy-resolution ion beam. TheE R=272 keV resonance was found to consist of two states separated by (888+5) eV, where the lower (higher) energy member is a high-spin (low-spin) state. All four resonances have widths less than a few eV, which is an improvement of nearly two orders of magnitude below previously reported limits. The influence of atomic effects on the determination of the correct value for the resonance energy is examined.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01291537
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  • 4
    Digitale Medien
    Digitale Medien
    The effects of electron screening and resonances in (p, α) reactions on10B and11B at thermal energies (1993)
    Springer
    The European physical journal 345 (1993), S. 231-242 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 25.40
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The fusion reactions10B(p, α)7Be and11B(p, α)8Be have been studied over the c.m. energy range E=17 to 134 keV using intense proton beams and thick solid targets. In the case of11B(p, α)8Be the low-energy data in terms of the astrophysical S(E) factor show an exponential enhancement (up to a factor of 1.9) due to the effects of electron screening, where the deduced screening potential is larger than expected. In the case of10B(p, α)7Be the low-energy data exhibit an enhancement by more than a factor of 200, which cannot be explained by the effects of electron screening. The enhancement arises here from the high-energy tail of an expecteds-wave resonance at ER=10 keV. The results offer an improved prospect for this reaction as advanced fuel in future fusion reactors than previously envisioned.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01293350
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  • 5
    Digitale Medien
    Digitale Medien
    The3He(d,p) α reaction at astrophysical energies (1989)
    Springer
    The European physical journal 333 (1989), S. 219-227 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 21.60.Gx ; 25.55.-e ; 24.10.Eq
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01565154
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  • 6
    Digitale Medien
    Digitale Medien
    Atomic effects on α-α scattering to the8Be ground state (1992)
    Springer
    The European physical journal 344 (1992), S. 205-217 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 24.30.−v
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Theα-α scattering to the8Be ground state was investigated in kinematic coincidence for the angle pairs 45
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01291705
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  • 7
    Digitale Medien
    Digitale Medien
    The S(E) factor of7Li(p, γ)8Be and consequences for S(E) extrapolation in7Be(p, γ0)8B (1995)
    Springer
    The European physical journal 351 (1995), S. 229-236 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 25.40
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Excitation functions and forward-backward anisotropies have been measured for the7Li(p, γ)8Be capture reaction over the proton energy rangeE p =100 to 1500 keV, using a 4π summing crystal and Ge(Li) detectors, respectively. The data show at all energies the presence of El and M1 capture amplitudes arising from the direct capture (DC) process and theE R =441 and 1030 keV resonances, respectively. Due to the observed DC process, the present data increase significantly the reaction rates (up to a factor of 110) compared to values given in the compilation. The data and their analyses remove the recent criticism on DC model calculations, which had implied a significant reduction in the extrapolated S(E) factor for7Be(p,γ)B and thus in the predicted flux of high-energy solar neutrinos; thus, the solar neutrino problem is still with us.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01289534
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