Our understanding of the universe and the standard model of particle physics has reached an incredible level of depth and accuracy. Nevertheless, there are still very fundamental questions, for example, what is the nature of dark matter or why does the universe consist of matter and not in equal parts of antimatter. Experiments in underground laboratories with xenon-based detectors play a crucial role in answering these questions.
One major challenge is that the sensitivity of the detectors increases with their size, thus also increasing the rate of background signals due to radioactivity in the detector construction materials. Therefore, the purity of the detector materials must be reduced further and further, which is achieved first by careful material screening and selection. Secondly, the actual detector medium, liquid xenon, is shielded from the detector construction materials by sophisticated methods. This leaves the radioactive noble gases (radon and some isotopes of krypton and argon) in the liquid xenon as the main problem.
The goal of the LowRad project (Low radon and low internal radioactivity for dark matter and rare event xenon detectors) is to develop the technologies for reducing these radioactive noble gas impurities in liquid xenon (1 rad on atom per more than 100 moles xenon) for the next generation of a xenon-based observatory such as XLZD/DARWIN that they each cause a background rate an order of magnitude lower than that of the unshieldable solar and atmospheric neutrinos. In particular, cryogenic distillation methods combined with ultrasensitive diagnostic methods are being developed. The devices used must have a very low radioactive background rate and, in particular, an extremely low radon emanation rate. Therefore, practically all parts of the apparatus must be specially developed for this purpose. To provide the enormous cooling capacity required, a cryogenic heat pump technology is being developed. In a final demonstrator, these new methods will be combined with the removal of electronegative impurities from xenon and with calibration methods using short-lived radioactive noble gases.
The outcomes of this project will be crucial to significantly increase the sensitivity of the next generation of xenon-based detectors in the search for dark matter, neutrinoless double beta decay and other rare or exotic events. In addition, the development of high-purity instrumentation and equipment and the various methods can also be applied in other fields.
