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

Abstract

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.