Neutron inelastic scattering processes as a background for double-β decay experiments

Abstract

We investigate several Pb$(n,n^{\text{'}}\gamma$) and Ge$(n,n^{\text{'}}\gamma$) reactions. We measure γ-ray production from Pb$(n,n^{\text{'}}\gamma$) reactions that can be a significant background for double-β decay experiments which use lead as a massive inner shield. Particularly worrisome for Ge-based double-β decay experiments are the 2041-keV and 3062-keV γ rays produced via Pb$(n,n^{\text{'}}\gamma$). The former is very close to the ${}^{76}\mathrm{Ge}$ double-β decay endpoint energy and the latter has a double escape peak energy near the endpoint. We discuss the implications of these γ rays on past and future double-β decay experiments and estimate the cross section to excite the level that produces the 3062-keV γ ray. Excitation γ-ray lines from Ge$(n,n^{\text{'}}\gamma$) reactions are also observed. We consider the contribution of such backgrounds and their impact on the sensitivity of next-generation searches for neutrinoless double-β decay using enriched germanium detectors.