187-Re/187-Os – Nuclear Chronometer for the Age of the Universe

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• Franz Käppeler (Karlsruhe Institute of Technology)
• Thursday 09 June 2011, 15:00-16:00
• W103.

If you have a question about this talk, please contact Carl Wheldon.

Accurate neutron capture cross sections of 186-Os and 187-Os are crucial for deriving the s-process abundance of 187-Os at the formation of the solar system. With that information it is possible to determine the radiogenic abundance component of 187-Os originating from the decay of the unstable isobar 187-Re (t1/2 = 41.2 Gyr) and to infer the time of active nucleosynthesis in the Galaxy. The neutron capture cross sections of 186-Os, 187-Os, and 188-Os have been measured at the CERN n_TOF facility from 1 eV to 1 MeV, covering the entire energy range of astrophysical interest. In parallel, the inelastic neutron-scattering cross section of 187-Os was determined in a time-of-flight experiment at the Karlsruhe 3.7-MV Van de Graaff accelerator using an almost mono-energetic beam of 30-keV neutrons. From these results a comprehensive experimental basis was derived for calculations of the stellar neutron capture rates in terms of the Hauser-Feshbach statistical model, with particular emphasis on a consistent treatment of the contribution by thermally populated excited states. Maxwellian averaged cross sections were obtained over the full temperature range of current s-process scenarios. The consequences for the s component of the 187-Os abundance and the related impact on the time duration of Galactic nucleosynthesis via the Re/Os cosmo-chronometer are discussed.

This talk is part of the Nuclear physics seminars series.

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• Nuclear physics seminars
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