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Träfflista för sökning "WFRF:(Wilhelmsen L) ;pers:(Jonson Björn 1941);pers:(Franchoo S.)"

Search: WFRF:(Wilhelmsen L) > Jonson Björn 1941 > Franchoo S.

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1.
  • Fynbo, H. O. U., et al. (author)
  • Revised rates for the stellar triple-alpha process from measurement of C-12 nuclear resonances
  • 2005
  • In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687 .- 1476-4679. ; 433:7022, s. 136-139
  • Journal article (peer-reviewed)abstract
    • In the centres of stars where the temperature is high enough, three alpha-particles (helium nuclei) are able to combine to form C-12 because of a resonant reaction leading to a nuclear excited state(1). (Stars with masses greater than similar to0.5 times that of the Sun will at some point in their lives have a central temperature high enough for this reaction to proceed.) Although the reaction rate is of critical significance for determining elemental abundances in the Universe(1), and for determining the size of the iron core of a star just before it goes supernova(2), it has hitherto been insufficiently determined(2). Here we report a measurement of the inverse process, where a C-12 nucleus decays to three alpha-particles. We find a dominant resonance at an energy of similar to11 MeV, but do not confirm the presence of a resonance at 9.1 MeV (ref. 3). We show that interference between two resonances has important effects on our measured spectrum. Using these data, we calculate the triple-a rate for temperatures from 10(7) K to 10(10) K and find significant deviations from the standard rates(3). Our rate below similar to5 x 10(7) K is higher than the previous standard, implying that the critical amounts of carbon that catalysed hydrogen burning in the first stars are produced twice as fast as previously believed(4). At temperatures above 10(9) K, our rate is much less, which modifies predicted nucleosynthesis in supernovae(5,6).
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2.
  • Fynbo, H. O. U., et al. (author)
  • News on C-12 from beta-decay studies
  • 2004
  • In: Nuclear Physics A. - : Elsevier BV. - 0375-9474. ; 738, s. 59-65
  • Conference paper (peer-reviewed)abstract
    • We discuss the importance of the spectroscopic properties of the resonances of C-12 just above the 3alpha-threshold, and review the existing experimental information of this region with emphasis on 0(+) and 2(+) states. A new experimental approach for studying the beta-decays of B-12 and N-12 is presented based on techniques developed in the context of Radioactive beam (rare isotope) physics. Finally preliminary results from an ongoing analysis of two recent experiments are given.
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