Dan Baxter with Dan Akerib and Tom Shutt
Removal of trace krypton from xenon using charcoal chromatography in the saturated regime
Liquid xenon experiments are becoming more prominent as a viable way to search for dark matter. In these experiments, it is important to use liquid Xenon free of any radioactive impurities. A main source of impurities is Krypton, which must be removed. Since Xenon of necessary purity is not available commercially, the Krypton must be removed in laboratories, in our case by a process of removing the Krypton through chromatography. Chromatography is the study of separating gases by passing them through an absorbing material, in our case charcoal, with a carrier gas. Xenon and Krypton will pass through at different speeds due to different absorption constants. While this process is relatively well studied, the removal system is generally saturated with large amounts of the mixture to expedite the removal process. Under saturation, nearly all of the binding sites in the charcoal become used, so some gas that otherwise would have been absorbed passes through much more quickly. Under this scenario, the process no longer follows the well-studied model and is the focus of this experiment. As part of this project, a setup must be constructed capable of running controlled amounts of Helium carrier gas and Xenon through charcoal at controlled flow rates in order to study the chromatography within the saturated regime. This setup will require knowledge of orbital tube welding and other basic machining skills in addition to introducing computer controlled readout. Variables which are to be adjusted in the process include the Helium flow rate and pressure, as well as the Xenon mass fraction. Removal of Krypton by this process is known to work, and through trial and error has been optimized, but has not as of yet been quantified. Ultimately, the goal is to produce a model for the removal process that can be utilized during the production phase of future liquid Xenon dark matter experiments.