O Reaction in the Calibration Data of MAJORANA DEMONSTRATOR Experiment *

The MAJORANA DEMONSTRATOR experiment at the 4850’ level of the Sanford Underground Research Facility in Lead, SD has been searching for neutrinoless double-beta decay in ⁷⁶Ge using high purity germanium (HPGe) detectors. Data-taking with 30-kg of enriched detectors was successfully concluded in March 2021 and the natural detectors are still taking data for background studies. These HPGe detectors are calibrated with gamma rays from ²²⁸Th line sources deployed during energy calibrations. The HPGe detectors of the DEMONSTRATOR have achieved a great energy performance that extends from 1 keV to 10 MeV, including a record energy resolution of 2.5 keV FWHM at the 2039-keV Q-value. Alpha particles are also produced by the ²²⁸Th decay chains within the calibration sources, and they can induce (α, n) reactions on certain isotopes in the epoxy and plastic materials that encapsulate the line sources. In this talk, we will update the status of our investigation of ¹³C (α, n)¹⁶O reactions in MAJORANA calibration data based on the detection of 6.13 MeV de-excitation gammas, which are from excited ¹⁶O states produced in the (α, n) reactions.