Experimental studies related to s-process abundances

The accurate determination of the neutron capture cross sections at stellar temperatures of kT = 10-100 keV is an essential prerequisite for investigations of the nucleosynthesis of heavy elements. For this purpose a 4 pi Barium Fluoride Detector was constructed at Karlsruhe and implemented at the 3.75MV Van de Graaff accelerator. This detector combines high efficiency with good energy resolution for the detection of gamma-rays, and allows to register capture events with a probability of similar to 98%. Neutrons are produced by the Li-7(p,n)Be-7 reaction. Over the last decade the cross sections of 57 isotopes have been measured in the mass range from Cd to Ta with typical uncertainties of 1-2%, an improvement of factors 5-10 compared to other methods. These data were used in extensive s-process studies based on phenomenological and stellar models for deriving reliable sets of s- and r-process abundances.