The stellar neutron capture cross sections of 186Os and 187Os are fundamental for the Re/Os
cosmo-chronometer since they are de ning the s-process abundance of 187Os. Subtraction of the
s-component from the solar 187Os abundance yields the radiogenic contribution to 187Os due to
b -decays of 187Re (t1=2 = 42.3 Gy) originating from r-process nucleosynthesis. The laboratory
cross section of 187Os requires a signi cant correction for the effect of the low-lying excited state
at 9.75 keV, which is strongly populated under stellar conditions. This reliability of the theoretical
correction can be greatly improved by an experimental determination of the cross section for inelastic
scattering to the 9.75 keV state. In this work, high resolution time-of- ight measurements
of (n;g ) cross sections of 186;187;188Os from 1 eV to 1 MeV performed at the CERN n_TOF facility
are reported. The inferred stellar cross sections differ from previously recommended values.
In addition, the inelastic scattering cross section has been measured at 30 keV neutron energy via
time-of- ight at the Karlsruhe 3.7 MV Van de Graaff. The implications of these results for the
Re/Os clock are brie y discussed.
CitacióCalviño, F. [et al.]. Experimental challenges for the Re/Os clock. A: Nuclei in the Cosmos. "NIC IX: International Symposium on Nuclear Astrophysics — Nuclei in the Cosmos — IX". CERN Geneva: 2006, p. 1-8.