Johanna Wydra

We present a novel device for the inline activity monitoring of gaseous tritium, named “Gaseous Tritium Activity Monitoring with Scintillators” (GaTAMOS). Unlike established methods that often rely on liquid scintillation or plastic scintillators with limited chemical resistance, this system utilizes a chemically inert, inorganic Terbium-activated Gadolinium Oxysulfide (Gd2O2S:Tb) ceramic. A specialized soldering technique was developed to join the ceramic scintillator to a stainless-steel flange, achieving a vacuum-tight seal (95% of residual contamination within minutes. The proposed system offers a compact, robust, and cost-effective alternative to ionization chambers or BIXS systems for process monitoring in tritium handling facilities.

I. Over recent decades, the importance of tritium has increased dramatically, mainly caused by fusion technology [1–4], which uses tritium as as fuel for clean, base load power generation. As the d...

The tangential momentum accommodation coefficient (TMAC) describes to what degree the interaction of a molecule with a surface is specular or diffuse and is therefore an important quantity for gas dynamics simulations and tritium processing in future fusion power plants. To the best of our knowledge, up to now, no TMAC values for tritium can be found in literature: neither ab initio calculated nor experimentally obtained. At the Tritium Laboratory Karlsruhe (TLK), with a license to handle up to 40 g of tritium, we have set up a cryogenic viscosity measurement apparatus (Cryo-ViMA) experiment aimed at measuring the viscosity of tritium. The Cryo-ViMA setup is based on a spinning rotor gauge, with a stainless steel rotor. The measurement principle and accuracy have been verified using helium, hydrogen, and deuterium. In this measurement, the normalized deceleration rate (DCR) of the spinning rotor is measured as a function of the pressure of the surrounding dilute gas. In addition to the viscosity, the analysis of the data acquired in this manner allows access to the velocity slip coefficient (VSC), from which the TMAC can be extracted as described in (Tekasakul et al., 1996). Therefore, the measurement data from (Wydra, 2025) will be used in this article to calculate the VSC and the TMAC. The Cryo-ViMA setup allows for cooling over a wide temperature range using evaporated liquid nitrogen. With slow thermal cycling, this system enables a high-resolution measurement of the temperature dependence of the TMAC between 110 and 300 K. The results of these measurements show that for the VSC, the values for H₂ and D₂ range from 1.25 to 1.4, depending on the temperature, whereas for T₂, the VSC is approximately 1.15. This leads to values for the TMAC for H₂ and D₂ between 0.80 and 0.87, whereas the TMAC of T₂ is much closer to one with 0.93. Moreover, the results show that a simple extrapolation of the value for tritium from the other hydrogen isotopologues is insufficient.

Experimental values for the viscosity of the radioactive hydrogen isotope tritium (T$_2$) are currently unavailable in literature. The value of this material property over a wide temperature range is of interest for applications in the field of fusion, neutrino physics, as well as to test ab initio calculations. As a radioactive gas, tritium requires careful experiment design to ensure safe and environmental contamination free measurements. In this contribution, we present a spinning rotor gauge based, tritium compatible design of a gas viscosity measurement apparatus (ViMA) capable of covering the temperature range from 80 K to 300 K.

Experimental values for the viscosity of the radioactive hydrogen isotopologue tritium are still unknown in literature. Existing values from ab initio calculations disregard quantum mechanic effects and are therefore only good approximations for room temperature and above. To fill in these missing experimental values, a measurement setup has been designed, to measure the viscosity of gaseous hydrogen and its isotopologues (H$_2$, HD, HT, D$_2$, DT, T$_2$) at cryogenic temperatures. In this paper, the first results with this Cryogenic Viscosity Measurement Apparatus (Cryo-ViMA) of the viscosity of gaseous hydrogen between 200 K to 300 K are presented.