Measurement of the neutron-capture cross section of 76Ge and 74Ge below 15 MeV and its relevance to 0νββ decay searches of 76Ge

The neutron radiative-capture cross section of 76Ge was measured between 0.4 and 14.8 MeV using the activation technique. Germanium samples with the isotopic abundance of ∼ 86 % Ge 76 and ∼ 14 % Ge 74 used in the 0 ν β β searches by the GERDA and Majorana Collaborations were irradiated with monoenergetic neutrons produced at eleven energies via the H 3 ( p , n ) He 3 , H 2 ( d , n ) He 3 and H 3 ( d , n ) He 4 reactions. Previously, data existed only at thermal energies and at 14 MeV. As a by-product, capture cross-section data were also obtained for 74Ge at neutron energies below 8 MeV. Indium and gold foils were irradiated simultaneously for neutron fluence determination. High-resolution γ-ray spectroscopy was used to determine the γ-ray activity of the daughter nuclei of interest. For the 76Ge total capture cross section the present data are in good agreement with the TENDL-2013 model calculations and the ENDF/B-VII.1 evaluations, while for the Ge 74 ( n , γ ) Ge 75 reaction, the present data are about a factor of two larger than predicted. It was found that the Ge 74 ( n , γ ) Ge 75 yield in the High-Purity Germanium (HPGe) detectors used by the GERDA and Majorana Collaborations is only about a factor of two smaller than the Ge 76 ( n , γ ) Ge 77 yield due to the larger cross section of the former reaction.