Neutron Capture Cross Sections for the Re/Os Clock

The radioactive decay of 187Re → 187Os (t1/2 = 43 Gyr) is suited for dating the onset of heavy‐element nucleosynthesis. The radiogenic contribution to the 187Os abundance is the difference between the natural abundance and the corresponding s‐process component. This component can be obtained via the well‐established σN systematics using the neighboring s‐only isotope 186Os, provided the neutron‐capture cross sections of both isotopes are known with sufficient accuracy. We report on a new set of experiments performed with a C6D6 detector array at the n_TOF neutron spallation facility of CERN. The capture cross sections of 186Os, 187Os, and 188Os have been measured in the neutron‐energy range between 1 eV and 1 MeV, and Maxwellian‐averaged cross sections were deduced for the relevant thermal energies from kT=5 keV to 100 keV.