Neutron physics of the Re/Os clock. I. Measurements of the (n,gamma) cross sections of the 186,187,188-Os at the CERN n_TOF facility

The precise determination of the neutron capture cross sections of Os186 and Os187 is important to define the s-process abundance of Os187 at the formation of the solar system. This quantity can be used to evaluate the radiogenic component of the abundance of Os187 due to the decay of the unstable Re187 (t1/2=41.2 Gyr) and from this to infer the time duration of the nucleosynthesis in our galaxy (Re/Os cosmochronometer). The neutron capture cross sections of Os186, Os187, and Os188 have been measured at the CERN n-TOF facility from 1 eV to 1 MeV, covering the entire energy range of astrophysical interest. The measurement has been performed by time-of-flight technique using isotopically enriched samples and two C6D6 scintillation detectors for recording the prompt γ rays emitted in the capture events. Maxwellian averaged capture cross sections have been determined for thermal energies between kT=5 and 100 keV corresponding to all possible s-process scenarios. The estimated uncertainties for the values at 30 keV are 4.1, 3.3, and 4.7% for Os186, Os187, and Os188, respectively. © 2010 The American Physical Society