Experimental study of 13C({\alpha},n)16O reactions in the Majorana Demonstrator calibration data

TL;DR

This study measures and compares the rate of 13C(α,n)16O reactions in the Majorana Demonstrator, confirming the reliability of background models for rare event searches using germanium detectors.

Contribution

It provides the first experimental validation of 13C(α,n)16O reaction rates in the context of the Majorana Demonstrator calibration data, supporting background estimations for double-beta decay experiments.

Findings

Observed 6129-keV gamma-ray rates match TALYS predictions within uncertainties.

Reactions contribute to background understanding in ultra-rare event searches.

Supports future background projections in double-beta decay experiments.

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($\alpha,n)^{16}$O reactions induced by $\alpha$-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 $\gamma$-rays emitted from the excited $^{16}$O states that are populated when the incoming $\alpha$-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 ($\alpha,n$)-reactions in future double-beta decay search efforts.