Neutron capture cross sections of 184W and 186W

The neutron capture cross sections of 184W and 186W have been determined by means of the activation technique. The measurements were carried out at the Karlsruhe 3.75-MV Van de Graaff accelerator using the 7Li(p,n)7Be reaction for neutron production. Samples of natural composition were irradiated in a quasistellar neutron spectrum for a thermal energy of kT=25 keV. Systematic uncertainties were investigated by variation of the experimental parameters in repeated activations. The induced activities were counted with HPGe detectors via the strongest γ-ray lines in the decay of the respective product nuclei. The measured data were converted into Maxwellian averaged cross sections at kT=30 keV, yielding 221±12 mb and 231±11 mb for 184W and 186W, respectively. Together with the result of a previously reported measurement on 180W, the present values can be used to improve the cross-section trend with neutron number, which is important for extrapolation into the regions of unstable isotopes. These results are of interest for stellar and explosive nucleosynthesis in nuclear astrophysics as well as for technological applications.