Liquid Xenon Purification for Dark Matter Detection

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This proposal requests support for a Princeton group to develop a liquid xenon purification technique for a Dark Matter detector. It now appears certain from astrophysical measurements that some 30% of the total amount of material in the universe is composed of some new form of "dark matter". This dark matter is distinct from the atoms that make up the everyday matter we are familiar with, and is so named because it does not emit light, or interact with matter in an ordinary way. Instead, the evidence for dark matter comes from the gravitational attraction this matter exerts in a wide range of astrophysics systems, from galaxies at the small end, to the largest groupings of galaxies known in the universe. Without knowing with certainty what this matter is, it is thought likely that dark matter may occasionally collide with the atoms of ordinary matter. Because our galaxy is also full of dark matter, a sensitive enough particle detector, analogous to a Geiger counter, could see collisions of these particles here on Earth. However, ordinary levels of natural radioactive backgrounds must be reduced enormously for this idea to have a chance of detecting these ghostly particles. A number of groups are developing detectors based on a liquefied form of the inert gas xenon. The liquid xenon will serves as the target to be struck by the dark matter particle. Xenon naturally occurs in air at a low level, and, when separated from air commercially, contains some amount of krypton, another inert gas. A problem is that krypton contains trace amounts of a radioactive isotope, which, while negligible for human health, is a serious problem for xenon-based dark matter experiments. The PI proposes to develop a new method to remove Kr from Xe to the level needed for these experiments.