Neutron inelastic scattering and reactions in natural Pb as a background in neutrinoless double-β-decay experiments

Inelastic neutron scattering and reactions on Pb isotopes can result in γ rays near the signature end-point energy in a number of ββ isotopes. In particular, there are γ-ray transitions in Pb206,207,208 that might produce energy deposits at the Ge76Qββ in Ge detectors used for 0νββ searches. The levels that produce these γ rays can be excited by (n,n'γ) or (n,xnγ) reactions, but the cross sections are small and previously unmeasured. This work uses the pulsed neutron beam at the Los Alamos Neutron Science Center to directly measure reactions of interest to ββ-decay experiments. The cross section on Pbnat to produce the 2041-keV γ ray from Pb206 is measured to be 3.6 ± 0.7 (stat.) ± 0.3 (syst.) mb at 9.6 MeV. The cross section on Pbnat to produce the 3061,3062-keV γ rays from Pb207 and Pb208 is measured to be 3.9 ± 0.8 (stat.) ± 0.4 (syst.) mb at the same energy. We report cross sections or place upper limits on the cross sections for exciting some other levels in Pb that have transition energies corresponding to Qββ in other ββ isotopes.