Neutron capture of the bottleneck isotopes Ba-138 and Pb-208, s-process studies, and the r-process abundance distribution

The capture cross sections of Ba-138 and Pb-208 have been measured by time-of-flight (TOF) at the electron linear accelerator GELINA in the energy range from 200 eV to 200 keV. The Maxwellian averaged capture (MAC) cross sections were determined versus temperature kT between 5 and 100 keV. The data were applied to carry out new parametric studies of the s-process. Two parameterized models were considered, pulsed s-process with one neutron source and double-pulsed s-process, the combined burning of two neutron sources. Through the s-process abundance distribution the complementary semiempirical p-process and r-process abundance distributions were determined. Especially the termination of the s-process was investigated. It was found that in the frame of the double-pulse s-process model only negligible amounts of Bi-209 are synthesized. This would mean that bismuth is mainly an r-process element.