The Karlsruhe Tritium Laboratory (TLK) of the Karlsruhe Institute für Technology (KIT) is one of the world’s largest civil laboratories dedicated to research the properties and possible applications of the radioactive hydrogen isotope tritium. For instance, tritium is a pure beta emitter which emits comparatively low-energy electrons of 18.6 keV during radioactive decay. The different radiochemical properties of tritium creates additional challenges and advantages in hydrogen science and technology compared to handling and using ordinary hydrogen.

Therefore, is very important for various applications to be able to determine the composition and quantity of gases containing tritium during handling at any time. To be more specific the detection method needs to work in a pressure range of approx. 1-1000 mbar, does have an accuracy better than 3% and has to offer the ability to differentiate between all hydrogen isotopologues (H2, D2, T2, HD, HT, DT). In addition, the detection method must be easy to integrate into existing systems by a compact design, be as maintenance-free as possible and has to function contactless avoiding radioactive waste and contamination. All these requirements are fulfilled by the technique of Raman spectroscopy.

Commercially available Raman systems are usually unsuitable due to the use of non-tritium-compatible materials (mostly polymers), inadequate detection limits or the sheer size of the system. Therefore, a compact Raman system is currently being developed at the TLK that meets all of the criteria mentioned before. The system is completely fiber-coupled to eliminate the high effort linked with the alignment of free-space optic. This enables the system to function reliably under the semi-industrial conditions in the laboratory. The optical setup uses an actively cooled CCD spectrometer to detected and evaluate the Raman spectra which is generated by fiber coupled laser light source. The laser light emission and the spectra collection in the tritium-carrying vacuum system is achieved via a special Raman head containing all the required optics and a metallically sealed connection (CF-compatible ultra-high vacuum flange). The excitation light source LambdaBeam offers a 200 mW monochromatic line at 532 nm for Raman signal generation. The DPSS laser is developed and produced at RGB Lasersystems in Kelheim Germany.

The described system is currently in its final tests and achieves a detection limit of approx. 0.5 mbar for all hydrogen isotopologues, it can be integrated into existing systems within a very short time and can be used for extensive measurement campaigns under 24/7 operation.

Complete Raman system with Raman head (right), spectrometer (back) and RGB Lasersystems 532 nm laser. For passive cooling, all components are mounted on a compact passiv heat sink (approx. 15cm x 20cm).

RGB thanks Mr. Florian Priester and his team of TLK & KIT