Observation of Low-Energy Surface Photon Events with a Point Contact Germanium Detector

Point contact germanium detectors lead the field in the search for neutrinoless double-beta decay (0vBB), and they have been used to achieve one of the greatest half-life sensitivities to date. These detectors have excellent energy resolution, low noise, and low-energy thresholds, making them well suited for a variety of rare event searches. One aspect of germanium detectors that is difficult to characterize is their passivated surface. Data from the MAJORANA Collaboration, which searches for 0vBB, shows the presence of a 46.5 keV gamma ray peak from Pb-210, but the absence of its 10.8 keV peak. It is hypothesized that passivated surface effects are the cause of this unexpected result. To understand the response of the passivated surface to low-energy photon events more thoroughly, we have designed an x-ray fluorescence source of variable x-ray energy using a collection of various foils. Using this source, we aim to build a more complete model of the passivated surface that will allow backgrounds for the MAJORANA Collaboration to be more accurately modeled.