Inelastic neutron scattering studies of ⁷⁶Ge and ⁷⁶Se: Relevance to neutrinoless double-β decay

Inelastic neutron scattering measurements were performed at the University of Kentucky Accelerator Laboratory on enriched ⁷⁶Ge and ⁷⁶Se scattering samples. From measurements at incident neutron energies from 2.0 to 4.0 MeV, many new levels were identified and characterized in each nucleus; level lifetimes, transition probabilities, multipole mixing ratios, and other properties were determined. In addition, γ-ray cross sections for the ⁷⁶Ge(n,n′γ) reaction were measured at neutron energies up to 5.0 MeV, with the goal of determining the cross sections of γ rays in 2040-keV region, which corresponds to the region of interest in the neutrinoless double β decay of ⁷⁶Ge. Gamma rays from the three strongest branches from the 3952-keV level were observed, but the previously reported 2041-keV γ ray was not. Population cross sections across the range of incident neutron energies were determined for the 3952-keV level, resulting in a cross section of ∼0.1 mb for the 2041-keV branch using the previously determined branching ratios. Beyond this, the data from these experiments indicate that previously unreported γ rays from levels in ⁷⁶Ge can be found in the 2039-keV region.