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Abstract

The Xenon1T experiment aims for the detection of dark matter with liquid xenon as target material for scattering events of so-called WIMPs (Weakly Interacting Massive Particles), which represent one of the main candidates for particle dark matter. Due to the expected very low event rate of this process, ultra-low background conditions are required to reach the sensitivity necessary for WIMP detection. Among the most serious internal background contributions is the radioactive krypton isotope ⁸⁵Kr, which is intrinsically present in commercially available xenon at the ppm or ppb level, and, as a β-emitter, produces signals in the detector that can mimic the searched-for WIMP signals. How-ever, krypton traces are successfully reduced from liquid xenon by cryogenic distillation. This thesis has been carried out in the context of monitoring krypton traces, using a gas-chromatographic mass spectrometry setup (RGMS) for an off-line krypton in xenon assay. We develop a novel data analysis procedure that allows to be sensitive to krypton in xenon concentrations of 10 ppq at 90 % C.L. for the RGMS conditions present during this work. We further present assay results covering three di˙erent xenon distillation campaigns. With these we verify the excellent performance of the cryogenic distil-lation column designed for and installed at Xenon1T and project the Xenon1T detector to preserve the required purity in krypton over months of operation.