The study of 13 C( α, n ) 16 O reactions in the Majorana Demonstrator calibration data

Neutron captures and delayed decays of reaction products are common sources of backgrounds in ultra-rare event searches. In this work, we studied 13 C( α, n ) 16 O reactions induced by α -particles emitted within the calibration sources of the Majorana Demonstrator . These sources are thorium-based calibration standards enclosed in carbon-rich materials. The reaction rate was estimated by using the 6129-keV γ -rays emitted from the excited 16 O states that are populated when the incoming α -particles exceed the reaction Q-value. Thanks to the excellent energy performance of the Demonstrator ’s germanium detectors, these characteristic photons can be clearly observed in the calibration data. Facilitated by Geant4 simulations, a comparison between the observed 6129-keV photon rates and predictions by a TALYS-based software was performed. The measurements and predictions were found to be consistent, albeit with large statistical uncertainties. This agreement provides support for background projections from ( α, n )-reactions in future double-beta decay search efforts.