Inelastic neutron scattering cross sections for Ge 76 relevant to background in neutrinoless double- β decay experiments

The experimental signature in searches for the neutrinoless double-β decay of Ge76 is a peak near 2039 keV in the spectrum. Given the low probability of the process, it is important that the background in this region be well understood. Inelastic scattering reactions with neutrons from muon-induced interactions and (α,n) reactions in the surrounding materials or in the detector can provide contributions to the background. We have measured the production cross sections for γ rays from the Ge76(n,n′γ) reaction in the 2039-keV region at incident neutron energies up to 4.9 MeV. In addition to determining that the cross sections of a previously known 2040.7-keV γ ray from the 3952-keV level in Ge76 are rather small, we find that a larger contribution arises from a 2037.5-keV γ ray which is attributed to a newly identified level at 3147 keV in Ge76. A third contribution is also possible from another new level at 3577 keV. These results indicate that the 2039-keV region in Ge76 neutrinoless double-β decay searches is more complex than was previously thought.