Instruments and Facilities

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).