The stellar neutron capture cross sections of 186 Os and 187 Os are fundamental for the Re/Os cosmo-chronometer since they are defining the s-process abundance of 187 Os. Subtraction of the s-component from the solar 187 Os abundance yields the radiogenic contribution to 187 Os due to β -decays of 187 Re (t 1/2 = 42.3 Gy) originating from r-process nucleosynthesis. The laboratory cross section of 187 Os requires a significant 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-flight measurements of (n, γ) cross sections of 186,187,188 Os 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-flight at the Karlsruhe 3.7 MV Van de Graaff. The implications of these results for the Re/Os clock are briefly discussed.

The n_TOF spallation neutron facility is operating at CERN since 2001. Neutrons are produced with a very wide energy range, from thermal up to 1 GeV and with a very high instantaneous flux (105n/cm2/pulse at 200 m from target) thanks to the high intensity (7 × 1012 protons/pulse) and low repetition rate of the Proton Synchrotron (PS) which is delivering protons to a lead spallation target. The experimental area is located at 200 m from the target, resulting in a very good energy resolution and beam quality thanks to the adoption of an optimal collimation system. At the end of 2008 the n_TOF facility has resumed operation after a halt of 3 years due to technical issues. This contribution will outline the main physics results obtained by the facility since its inception in 1999, and show the importance of the measured nuclear data in the field of Nuclear Astrophysics and Nuclear Technology. Then it will present the future perspectives of the facility, aiming mainly in the direction of measuring highly radioactive samples, for which the facility has unique capabilities, with a lower background

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