Experimental Challenges for the Re/Os Clock

The stellar neutron capture cross sections of 186Os and 187Os are fundamental for the Re/Os cosmo-chronometer since they are defining 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 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;gamma) 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-flight at the Karlsruhe 3.7 MV Van de Graaff. The implications of these results for the Re/Os clock are briefly discussed.

MOSCONI M.;  PLOMPEN Arjan;  RULLHUSEN Peter;  N_TOF COLLABORATION The; 

2007-01-25

Scuola Internazionale Superiore di Studi Avanzati / International School for Advanced Studies

JRC36206

https://publications.jrc.ec.europa.eu/repository/handle/JRC36206,