Neutron capture cross sections of 74Ge, 76Ge, and 75As at 25 keV

The neutron capture cross sections of Ge-74, Ge-76, and As-75 have been measured at the Karlsruhe Van de Graaff accelerator by means of the activation technique. The neutron source reaction Li-7(p,n)Be-7 was used for simulating a thermal energy distribution for kT=25 keV to determine the astrophysically relevant stellar cross sections directly. Based on an extended series of activations, consistent results could be obtained, corresponding to Maxwellian average cross sections at kT=30 keV of 37.6 +/- 3.9 mb for Ge-74, 21.5 +/- 1.8 mb for Ge-76, and 362 +/- 19 mb for As-75. These results are more accurate than previous data and are, therefore, important for resolving previous discrepancies. By extrapolation Maxwellian averaged cross sections were derived for thermal energies from 5 to 100 keV. The implications of these results for the s-process abundances in massive stars and for the background conditions in double beta decay experiments are discussed. .