Gas Extraction Lab
Tritium and He isotope samples are prepared for mass spectrometric measurement by using two vacuum extraction systems. Typically, we receive two types of water samples: small volume samples sealed in copper tubes (length: about 1 m; diameter: about 10 mm; volume: about 40 ml) and large volume samples collected in 1 l glass bottles.
Eight samples are connected to a vacuum extraction system held at a pressure of about 10E-6 to 10E-5 mbar. The copper tubes are opened and the water is expanded into a glass bulb. After quantitative transfer of all gases from the expansion bulb into a glass ampoule, the ampoule is flame sealed for storage of the samples. At this point, the water contained in the glass bulb is completely gas-free and can be flame sealed for 3He ingrowth from the tritium decay (tritiogenic 3He). After a period of typically about 6 months, the tritiogenic 3He is extracted from the glass bulbs and measured mass spectrometrically. If the tritium concentrations of the samples are very low or if a shorter ingrowth time is desired, we use a second extraction system designed for larger volumes. In this system, about 400 grams of water are transferred from the 1 l glass bottles into 1 l glass bulbs. After extraction of all gases under a vacuum of about 10E-3 mbar (3He extraction efficiency: >99.999 %), the glass bulbs are flame sealed for tritiogenic 3He buildup during storage in a freezer. The measurement procedure of the large volume samples is very similar to that used for small volume samples.
The design and performance of the two extraction systems used in the L-DEO noble gas laboratory are similar to those described by Bayer et al. (1989).
Bayer, R., P. Schlosser, G. Bönisch, H. Rupp, F. Zaucker, and G. Zimmek, Performance and blank components of a mass spectrometric system for routine measurement of helium isotopes and tritium by the 3He ingrowth method. Sitzungsber. der Heidelberger Akademie der Wissenschaften, Mathematisch Naturwissenschaftliche Klasse, Jahrgang 1989, 5, 241-279, Springer Verlag.