  In past decades a lot of progress has been made towards understanding the
main s-process component that takes place in thermally pulsing Asymptotic Giant
Branch (AGB) stars. During this process about half of the heavy elements,
mainly between 90<=A<=209 are synthesized. Improvements were made in stellar
modeling as well as in measuring relevant nuclear data for a better description
of the main s process. The weak s process, which contributes to the production
of lighter nuclei in the mass range 56<=A<=90 operates in massive stars
(M>=8Msolar) and is much less understood. A better characterization of the weak
s component would help disentangle the various contributions to element
production in this region. For this purpose, a series of measurements of
neutron-capture cross sections have been performed on medium-mass nuclei at the
3.7-MV Van de Graaff accelerator at FZK using the activation method. Also,
neutron captures on abundant light elements with A<56 play an important role
for s-process nucleosynthesis, since they act as neutron poisons and affect the
stellar neutron balance. New results are presented for the (n,g) cross sections
of 41K and 45Sc, and revisions are reported for a number of cross sections
based on improved spectroscopic information.
