Neutron Capture Measurements on the s-Process Termination Isotopes Lead and Bismuth

Resonance cross sections relevant for the termination of the s-process reaction path have been determined for 204,206,207Pb and 209Bi at the CERN neutron time-of-flight spectrometer n_TOF. Themeasurementswere carried out in the neutron energy range from1 eV up to 500 keV. By using a system of C6D6-detectors with optimized neutron sensitivity, the main corrections of previous measurements related to backgrounds from scattered neutrons could be practically eliminated. Other corrections were thoroughly treated by control measurements with additional samples for determination of the ambient background and of background from in-beam g -rays as well as by detailed analyses via Monte Carlo simulations. The Maxwellian averaged cross sections of the four isotopes and their implications for the s-process abundance contributions in the Pb/Bi region are discussed.