Online ²²² 222 Rn removal by cryogenic distillation in the XENON100 experiment

We describe the purification of xenon from traces of the radioactive noble gas radon using a cryogenic distillation column. The distillation column was integrated into the gas purification loop of the XENON100 detector for online radon removal. This enabled us to significantly reduce the constant ²²² Rn background originating from radon emanation. After inserting an auxiliary ²²² Rn emanation source in the gas loop, we determined a radon reduction factor of $$R\,>\,27$$ (95% C.L.) for the distillation column by monitoring the ²²² Rn activity concentration inside the XENON100 detector.