Speaker
Description
The control of chemical and radioactive contamination in argon is a key requirement for current and future large liquid-argon detectors. In this contribution, we discuss the use of inductively coupled plasma mass spectrometry (ICP-MS) as a fast and species-sensitive technique to complement detector-based purity observables, which are often indirect and require time-consuming data processing and analysis. The method provides direct access to trace contaminants in argon gas, including noble gas impurities such as krypton and xenon, identified through their characteristic isotopic patterns. As a specific application, we focus on the analysis of underground argon used in the DarkSide-50 experiment. Krypton contamination is unambiguously identified through the simultaneous observation of its stable isotopes, with relative intensities consistent with atmospheric krypton. From the measured stable krypton abundance, we infer the corresponding Kr-85 activity in underground argon. The result is in agreement with the independent Kr-85 activity measured by DarkSide-50 through the full detector-based analysis of physics data. This shows that ICP-MS can provide direct and quantitative information on radioactive contaminants in argon through a much shorter analysis chain than detector-based methods.