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Abstract:
The currently running Xenon100 experiment and its successor, Xenon1T, use liquid xenon
as target and detection material in the search for weakly interacting massive particles, a well
motivated candidate for dark matter in our universe. As the expected signal rate is less
than a couple of events per year, it is absolutely mandatory to understand and reduce the
possible background contributions. The man-made and almost pure beta-emitter 85Kr is a
very dangerous background candidate, as krypton is intrinsically present on the ppb (parts
per billion level b= 10−9) in commercially available xenon. Both further purification and
the corresponding analytics are therefore equally important for these kind of experiments.
This thesis describes two krypton in xenon measurement procedures and their impact on the
understanding of the krypton background in the Xenon experiments. First, a mass spectroscopic
set-up using gas-chromatographic pre-separation is introduced, and the improvements
in terms of stability and sensitivity down to the ppq (parts per quadrillion b= 10−15) regime
are highlighted. Subsequently several xenon assay results are presented: the evolution of the
krypton concentration in Xenon100 over a time period of more than a year is reconstructed
and linked to the observed radon decay rates. Furthermore, several distillation procedures
are examined, showing the high potential of cryogenic distillation for xenon purification.
Thereby, a measurement of ultra pure xenon with an so far unprecedented purity is presented.
Finally, a second analysis method is investigated, applying a delayed coincidence
analysis to the Xenon100 dark matter search data. This in-situ method is limited to the
ppt (parts per trillion b= 10−12) regime, but achieves very good agreements with the mass
spectroscopic results and confirms its absolute calibration.
