Neutron capture cross section ofAu197: A standard for stellar nucleosynthesis

We have measured the neutron capture cross section of gold using the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(p,n${)}^7$Be reaction for neutron production. This reaction not only provides the integrated neutron flux via the ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ activity of the target, but also allows for the simulation of a Maxwellian neutron energy spectrum at kT=25 keV. As this spectrum is emitted in a forward cone of 120° opening angle, the cross section can be measured in good geometry and independent of any other standard. Systematic uncertainties were studied experimentally in a series of activations. The final stellar cross section at kT=25 keV was found to be 648±10 mb, and extrapolation to the common s-process temperature kT=30 keV yields 582±9 mb. This result is used for renormalization of a number of cross sections which had been measured relative to gold.