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Abstract:
Dark matter composes 27% of the universe but its presence is inferred only
from gravitational phenomena. Direct detection experiments, such as Xenon1T,
attempt to detect the scattering of dark matter particles with the detector target,
in this case xenon nuclei. The experiment Xenon1T employs 3.3 tonnes of liquid
xenon in a Time Projection Chamber (TPC). The TPC is a detector that employs
electromagnetic fields in a sensitive volume for 3-d position reconstruction and
particle identification. Since dark matter scattering is a rare event, it is necessary
to reduce the background to improve the sensitivity of the detector. It is necessary
to monitor two kind of impurities in liquid xenon: radioactive impurities such as
krypton (present in commercially available xenon at ppb level), since it increases
the background, and electronegative molecules such as oxygen and water, since
they lower the electron life-time and disrupts the well functioning of the TPC. In
this work, the measurements of the xenon inventory prior to filling is presented
using the technique of gas chromatography. Some of the bottles measurements
are presented and the total purity is summarized. In the second part, a study
of gas mixing as solution of inconsistency measurements in the previous part is
presented, and different solutions to speed up the gas diffusion are tested. Finally,
since gas chromatography is not sensitive to helium, a measurement of the helium
concentration in the full xenon inventory is presented using the technique of mass
spectrometry.
