First measurement of the tritium viscosity in a temperature range from $100$K to $300$K

The viscosity of tritium is a crucial material property needed for a wide range of theoretical
and technological scientific fields, starting from fluid dynamics including vacuum science,
over astroparticle physics experiment like the Karlsruhe Tritium Neutrino Experiment
(KATRIN) to nuclear fusion for energy. Values found in literature are either ab initio
calculated by a classical approach neglecting quantum mechanical effects [Son16], or
extrapolated from hydrogen (H${}_2$) or deuterium (D${}_2$) by the square root of the mass ratios
[Kuc18], both with uncertainties of $2$% to $10$%. The lack of measurement data on material
properties of tritium is caused by the combination of it being an isotopologue of hydrogen,
the smallest existing molecule, which permeates even through metal, and its radioactive
nature, causing not only safety issues which have to be solved, but also radiolytic reactions.
For the measurement of the viscosity of tritium, a laboratory is needed with the license
to handle a significant amount of tritium. The Tritium Laboratory Karlsruhe (TLK) is a
unique facility in Europe with a license to handle $40$g of tritium with the ability to purify
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tritium up to $99$%, enabling the measurement of material properties such as the viscosity
of tritium. Within this work, the viscosity of T${}_2$ in the zero-density limit is measured with
an accuracy of $2.5$% in a temperature range from $100$K to $300$K. These measurements
first enable a test of the trueness of the aforementioned calculations, and second enlarge
the testbed for ab initio calculations regarding small non-spherical molecules including
plasmas, caused by the radioactivity of T${}_2$.

[Kuc18]: Laura Kuckert et al. In: Vacuum 158 (Dec. 2018), pp. 195–205. doi: 10.1016/j.vacuum.2018.09.036.
[Son16]: Bo Song et al. In: Journal of Chemical & Engineering Data 61.5 (May 2016). pp. 1910–1916. doi: 10.1021/acs.jced.6b00076.