Stellar neutron capture cross sections of $^{41}$K and $^{45}$Sc

The neutron capture cross sections of light nuclei (A<56) are important for s-process scenarios since they act as neutron poisons. We report on measurements of the neutron capture cross sections of K41 and Sc45, which were performed at the Karlsruhe 3.7 MV Van de Graaff accelerator via the activation method in a quasistellar neutron spectrum corresponding to a thermal energy of kT=25 keV. Systematic effects were controlled by repeated irradiations, resulting in overall uncertainties of less than 3%. The measured spectrum-averaged data have been used to normalize the energy-dependent (n,γ) cross sections from the main data libraries JEFF-3.2, JENDL-4.0, and ENDF/B-VII.1, and a set of Maxwellian averaged cross sections was calculated for improving the s-process nucleosynthesis yields in AGB stars and in massive stars. At kT=30 keV, the new Maxwellian averaged cross sections of K41 and Sc45 are 19.2±0.6 mb and 61.3±1.8 mb, respectively. Both values are 20% lower than previously recommended. The effect of neutron poisons is discussed for nuclei with A<56 in general and for the investigated isotopes in particular.