Measurement of the neutron-capture cross section of 76Ge and 74Ge below 15 MeV and its relevance to 0νββ0νββ 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%Ge76 and ∼14%Ge74 used in the 0νββ0νββ searches by the GERDA and Majorana Collaborations were irradiated with monoenergetic neutrons produced at eleven energies via the H3(p,n)He3, H2(d,n)He3 and H3(d,n)He4 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 Ge74(n,γ)Ge75 reaction, the present data are about a factor of two larger than predicted. It was found that the Ge74(n,γ)Ge75 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 Ge76(n,γ)Ge77 yield due to the larger cross section of the former reaction.