Development of internal radioisotope calibration sources for the nEXO experiment

The nEXO experiment is a proposed next-generation search for the neutrinoless double beta decay (NDBD) of Xe-136. The primary detector will be a 5-ton, monolithic liquid xenon time projection chamber (TPC) with the source enriched to 90% in the isotope of interest. To optimize the energy resolution and event reconstruction, calibrations are needed to map the spatial- and time-dependence of the detector's response, particularly in the central regions of the detector. While the baseline design of nEXO uses gamma-emitting radiation sources deployed outside the TPC, the strong attenuation in liquid xenon motivates the development of radioisotopes which can be injected into the liquid xenon and dissolved throughout the detector. In this talk, I will describe recent simulations and experimental tests of two such sources, Rn220 and Xe127, which are being studied for use in nEXO.