Neutron physics of the Re/Os clock. II. The (n, n′) cross section of 187Os at 30 keV neutron energy

The inelastic neutron-scattering cross section of Os-187 has been determined in a time-of-flight experiment at the Karlsruhe 3.7-MV Van de Graaff accelerator. An almost monoenergetic beam of 30-keV neutrons was produced at the threshold of the Li-7(p, n)Be-7 reaction. Information on the inelastic channel is required for reliable calculations of the so-called stellar enhancement factor, by which the laboratory cross section of Os-187 must be corrected in order to account for the thermal population of low-lying excited states at the temperatures of s-process nucleosynthesis, in particular of the important state at 9.75 keV. This correction represents a crucial step in the interpretation of the Os-187/Re-187 pair as a cosmochronometer.