A neutron source to measure stellar neutron capture cross sections at image Original Research Article

Since 1980 the 7Li(p,n)7Be reaction was intensively used for activation measurements. With a proton energy of Ep=1911 keV the resulting neutron spectrum resembles a Maxwell-Boltzmann distribution with a thermal energy of kT=25 keV. Therefore, this neutron source is ideal to determine Maxwellian-averaged neutron capture cross sections (MACS) close to a temperature of 250 million Kelvin (kT=23 keV) which is typical for the s process in red giant stars. Meanwhile, detailed stellar models indicate that the dominant neutron exposure of the main s-process component in low mass AGB stars occurs at a lower temperature of 90 million Kelvin (kT=8 keV). Hence, the necessary stellar reaction rates had to be extrapolated from 25 keV to the lower thermal energy. In order to avoid the corresponding additional uncertainties, we report on the 18O(p,n)18F neutron source, which allows one to produce a Maxwell-Boltzmann spectrum close to the lower thermal energy of kT=8 keV. First results of activation measurements for 138Ba(n,γ)139Ba, 139La(n,γ)140La, and 175Lu(n,γ)176Lum will be presented.