•Michael Heil1, S. Dababneh1, F. Käppeler1,
S. O' Brien2, R. Plag1 und R. Reifarth3
1Forschungszentrum Karlsruhe, Institut für Kernphysik,
Postfach 3640, D-76021 Karlsruhe, Germany
2Department of Physics, University of Notre Dame, Notre
Dame, IN 46556, USA
3Los Alamos National Laboratory, Los Alamos, New Mexico
87545, USA
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 takes place at a lower temperature of 90 million
Kelvin (kT=8 keV). In order to supply the necessary reaction rates for
the stellar models the values at 25 keV have to be extrapolated to the
lower thermal energy, introducing additional uncertainties. In this contribution
we report on a neutron source which allows to produce a Maxwell-Boltzmann
spectrum close to the lower thermal energy of kT=8 keV.