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Abstract

The radioactive isotope ²²²Rn is one of the most crucial intrinsic background sources for experiments dealing with a low event rate. Being a noble gas, it permanently emanates from almost all materials that are used in the detector. Its decay or the successive decays of its daughter isotopes can mimic the searched-for signal. This thesis was carried out in the context of the experiment XENON1T which aims at directly detecting weakly interacting massive particles (WIMPs), that could be a candidate for the postulated dark matter in the Universe. An extensive measurement campaign was performed in order to determine the ²²²Rn emanation rate of the detector components that will be in contact with the liquid xenon target. The individual results and an estimation of the detector’s overall emanation rate are reported in this work for the first time. For a further improvement of the detection of ²²²Rn with proportional counters, the sensitivity of the two counting gases ArCH₄ and XeCH₄ was studied in connection with different background shieldings. A direct comparison of the two counting gases makes an energy calibration necessary, the one for ArCH₄ was improved in the context of this work.