Dr. Christian Weinheimer – Radioactive cryogenic purification and low-contamination recirculating techniques for low-background noble gas experiments

With the installation of rare event search experiments in underground laboratories, passive and active shielding measures, careful material selection and surface treatments, radioactive isotopes in the xenon of xenon-based detectors have become the most important background source in the search for rare events besides solar and atmospheric neutrinos. Particularly important are radioactive noble gases, especially Rn-222 because of its gamma and beta-emitting progenies Pb-214, Bi-214 and Pb-210. In this talk, various methods for the continuous active removal of radon from xenon, in particular cryogenic distillation, will be presented.
New records in the purity of Ar-39, Kr-85 and Rn-222 have been achieved with cryogenic “online distillation” in the dark matter experiment XENONnT.
This presentation also provides an outlook on how these methods can be further developed to achieve the required purity of radioactive noble gases with a target concentration of 1 radon atom per 160 moles of xenon (or 0.1 µBq/kg) for the next generation of experiments such as XLZD, nEXO or NEXT.
In particular, developments within our ERC AdG project LowRad (No. 101055063) also aim to combine these methods with the purification from electronegative impurities and the required highly sensitive online diagnostic methods.