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  • 1995-1999  (3)
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  • 1
    Digitale Medien
    Digitale Medien
    The E1 and E2 capture amplitudes in 12C(α,γ0)16O (1999)
    Springer
    The European physical journal 6 (1999), S. 451-461 
    Details
    ISSN: 1434-601X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract. Excitation functions of the γ0 capture transition in 12C(α,γ)16O at θγ= 90˚ were obtained using a 4 × 4'' BGO crystal in close geometry (E= 0.94 to 3.39 MeV) and a 2 × 2'' BGO crystal in far geometry (E= 1.69 to 3.29 MeV), where the study of the reaction was initiated in inverse kinematics involving a windowless gas target. The small crystal detected essentially the E1 multipole component in the γ0 capture transition, while the large crystal observed approximately the angle-integrated sum of the E1 and E2 multipole components. Analysis of the two data sets together with data from previous work provided strong evidence that both multipoles are of equal importance at the relevant stellar energy E 0= 0.3 MeV.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100500050369
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  • 2
    Digitale Medien
    Digitale Medien
    Recoil separator ERNA: ion beam specifications (1999)
    Springer
    The European physical journal 6 (1999), S. 471-477 
    Details
    ISSN: 1434-601X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract. For improved measurements of the key astrophysical reaction 12C(α,γ)16O in inverted kinematics, a recoil separator ERNA is being developed at the 4 MV Dynamitron tandem accelerator in Bochum to detect directly the 16O recoils with about 50% efficiency. Calculations of the ion beam optics including all filtering and focusing elements of ERNA are presented. Since the 12C projectiles and the 16O recoils have essentially the same momentum, and since the 12C ion beam emerging from the accelerator passes through a momentum filter (analysing magnet), the 12C ion beam must be as free as possible from 16O contamination for ERNA to succeed. In the present work, the 16O contamination was reduced from a level of 1 × 10−11 to a level below 2 × 10−29 by the installation of Wien filters both before and after the analysing magnet. The measurement of these and other beam specifications involved other parts of the final ERNA layout – sequentially a Wien filter, a 60˚ dipole magnet, another Wien filter, and a ΔE-E telescope. The setup led to a measured suppression factor of 5 × 10−18 for the 12C ion beam. The experiments also indicate that an almost free choice of the charge state for the 16O recoils is possible in the separator.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100500050371
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  • 3
    Digitale Medien
    Digitale Medien
    Electron screening in backward elastic scattering (1998)
    Springer
    The European physical journal 2 (1998), S. 337-342 
    Details
    ISSN: 1434-601X
    Schlagwort(e): PACS:25.60.Bx Elastic scattering
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstact: The elastic scattering cross sections, σ (E,θ), for the systems He+Ta and He+W have been measured at θlab=165° and E lab=76.1 keV to 3.988 MeV using targets with a thickness of a few atomic layers. The results are smaller than the results given by the Rutherford scattering law, σR(E,θ), due to the effects of electron screening and can be described by σ(E,θ)/σR(E,θ)=(1+Ue/E)−1, where U e is an atomic screening potential energy. The deduced average value, U e=28 ± 3 keV, is consistent with the Moliére- and Lenz-Jensen-models as well as electron binding energies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100500050130
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