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

Abstract

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($\hat{I}\pm ,n{)}^{16}$O reactions induced by $\hat{I}\pm$-particles emitted within the calibration sources of the \textsc{Majorana Demonstrator}. These sources are thorium-based calibration standards enclosed in carbon-rich materials. The reaction rate was estimated by using the 6129-keV ${\hat{I}}^3$-rays emitted from the excited ${}^{16}$O states that are populated when the incoming $\hat{I}\pm$-particles exceed the reaction Q-value. Thanks to the excellent energy performance of the \textsc{Demonstrator}'s germanium detectors, these characteristic photons can be clearly observed in the calibration data. Facilitated by \textsc{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 ($\hat{I}\pm ,n$)-reactions in future double-beta decay search efforts.

Published version