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Determination of the Krypton-Impurity Evolution in the XENON1T Detector and Optimization of Separation Columns for Krypton in Xenon Assays

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Winkler,  Daniel
Division Prof. Dr. Manfred Lindner, MPI for Nuclear Physics, Max Planck Society;

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Citation

Winkler, D. (2020). Determination of the Krypton-Impurity Evolution in the XENON1T Detector and Optimization of Separation Columns for Krypton in Xenon Assays. Master Thesis, Ruprecht-Karls-Universität, Heidelberg.


Cite as: http://hdl.handle.net/21.11116/0000-0007-CFA8-3
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.