Measurement of the resonance capture cross section of 204,206-Pb and termination of the s-process

The neutron capture cross sections of 204;206Pb have been measured with high resolution at the n_TOF facility of CERN (Geneva) [5]. The neutron capture cross section of 204Pb is of particular relevance in astrophysics, since this s-only isotope constrains the branching of the reaction path at A = 204. The predicted abundance of this isotope is very sensitive to the details of the stellar model. Therefore, an accurate value of its capture cross section provides an important test and constraint for astrophysical models. 206Pb is representative of the entire reaction flow, thus its abundance scales with the inverse of the cross section, becoming practically independent of the specific stellar model employed. Consequently, its r-process abundance is well determined as the subtraction of the s-abundance from the total observed abundance. The r-process abundance is important as a constraint for the U/Th-cosmochronometer. Because of the occurrence (26%) of 206Pb in natural lead, its capture cross section is also important for the design of hybrid reactors based on Pb/Bi eutectic spallation sources