Stellar (n,γ) cross sections of neutron-rich nuclei

The neutron capture cross sections of neutron-rich nuclei are needed for nucleosynthesis studies of the heavy elements in the s and r processes. About half of the abundances between Fe and Bi are produced by the s process and the remaining part is due to the r process with a small contribution from the p process. The present results include the (n,γ) cross sections of 174,176Yb, 184,186W, 190,192Os, 196,198Pt, and 202,204Hg. These data are important for the determination of the s-process abundances and for deriving the r-process contribution to the solar system abundances. The measurements were carried at the Karlsruhe 3.7 MV Van de Graaff accelerator using the 7Li(p, n)7Be reaction for producing a quasi-stellar neutron spectrum. Activation in that spectrum allowed us to measure the Maxwellian averaged cross sections at a thermal energy of kT=25 keV. The experimental results were extrapolated from kT=25 keV to lower and higher temperatures.