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Abstract

The XENON experiment aims for the direct detection of dark matter with liquid xenon
as target material for so-called WIMPs (Weakly Interacting Massive Particles), which
represent one of the main candidates for particle dark matter. As the expected signal
rate is less than a couple of events per year, it is mandatory to understand and reduce
possible background contributions. The radioactive krypton isotope ⁸⁵Kr is among the
most serious internal background contributions, which can mimic a WIMP signal. However,
krypton traces are successfully removed from liquid xenon by cryogenic distillation. The
external monitoring of the remaining krypton traces using a rare gas mass spectrometer
(RGMS) sets the framework of this work. First, the krypton concentration evolution of the
XENON1T detector was determined. A change in the signal shape of RGMS required a new
analysis procedure, including a thorough and much improved error treatment. Within this
analysis, the lowest krypton in xenon concentration ever measured in a running detector
is set. Second, different adsorbents were examined and characterized to optimize the
separation of krypton from xenon, necessary for the present analysis of concentrations in
the ppq regime. Due to the posed requirements, such as resolution, peak width, and tailing,
the activated carbon ShinCarbon turned out to be the best candidate. The ShinCarbon
column will be an integral part of a planned system called AUTO-RGMS and will lead to a
significantly improved separation efficiency, a better reproducibility, and a lower detection
limit.