Stellar neutron capture cross sections ofK41andSc45

Abstract

The neutron capture cross sections of light nuclei ($Al56$) are important for $s$-process scenarios since they act as neutron poisons. We report on measurements of the neutron capture cross sections of $^{41}\mathrm{K}$ and $^{45}\mathrm{Sc}$, 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 $(n,\ensuremath{\gamma})$ 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 $^{41}\mathrm{K}$ and $^{45}\mathrm{Sc}$ are $19.2\ifmmode\pm\else\textpm\fi{}0.6$ mb and $61.3\ifmmode\pm\else\textpm\fi{}1.8$ mb, respectively. Both values are 20% lower than previously recommended. The effect of neutron poisons is discussed for nuclei with $Al56$ in general and for the investigated isotopes in particular.