Materials Radioassay Techniques for the nEXO Experiment O. Nusair for the nEXO Collaboration The University of Alabama

EXO-200 was a 200-kg-scale search for neutrinoless double-beta decay in isotopically enriched $^{136}$Xe, based on a single-phase liquid time projection chamber (TPC). nEXO is a 5000-kg-scale successor, presently in development, using a similar monolithic TPC concept. Both experiments require extremely low backgrounds, in order to achieve sensitivity targets on the order of $10^{26}$ and $10^{28}$ years, respectively. To this end, EXO-200 implemented a rigorous materials screening program prior to construction, in order to minimize intrinsic backgrounds from radioactivity in detector and shielding components. Operational data shows this approach to have been both effective in minimizing materials backgrounds and accurate in predicting overall detector backgrounds. nEXO has continued this campaign with even more stringent requirements. This talk will discuss radioassay techniques implemented by the nEXO collaboration. Constraints obtained by low-background gamma ray spectroscopy, neutron activation analysis, and mass spectrometry will be presented.