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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.
