It is well known that tritium, the hydrogen isotope 3H, is part of nuclear weapons and was spread all over the world as a consequence of nuclear bomb explosions. Rarely it is regarded as being “natural”, but actually it is. Long time before humans appeared tritium already existed on earth for a long time. This “natural” tritium is the product of cosmic radiation interactions with the atmosphere (mainly N-14). Nowadays this kind of tritium production contributes only to a small extent to the atmospheric tritium. Tritium is radioactive and decays with a half-life of 4.500 days under the emission of a very low energetic beta-particle. In the atmosphere tritium can be found within water vapour (HTO), hydrogen (HT) or methane (CH3T). Yet, the main portion of tritium released during the 1960’s has already been eliminated from the atmosphere by radioactive decay and precipitation. A large amount is captured in the oceans. Indeed, today anthropogenic sources releasing tritium to the environment can still be found. At the end of the 1980‘s contacts with research institutes in former Eastern Bloc countries lead to the idea of establishing a tritium sampling network. The primary goal was the documentation of atmospheric tritium. Statements about potential releases and their sources and the radiation hazards associated should be obtained. Furthermore it might help with the verification of meteorological models. To acquire comparable results a standardised sampling device was developed. This system simultaneously collects samples of air humidity and hydrogen. It was planned to enlist the gathered data in a database and to use them for the following subjects: • observation of local and global tritium transport in the atmosphere • detecting tritium releases and locating their sources • radiation risk evaluation • examining the transmutation of elemental hydrogen into water under natural conditions With the breakdown of the Eastern Bloc the idea of this common network faded away. At the moment only at two stations in Austria air humidity and air hydrogen are collected as planned: since 1991 at Research Center Arsenal in Vienna and since 1999 at Hoher Sonnblick a high mountain station (3160 m). Currently we are working together with the IAEA on a project with the aim to find a model, which helps evaluating weather conditions and in particular the climatic processes. As for these investigations the stable isotopes H-2 and O-18 are used and the currently used device introduces fractionation a new method is developed right now. Since the specific tritium activity concentration is not affected by air pressure or humidity the values for the two locations can be compared directly. In general the measured values are similar but sometimes differ noticeably. For example a peak value for the tritium activity concentration observed during March 2000 at Sonnblick was not noticed in Vienna. In this context the attempt should be made to analyse the air flows with the help of trajectories. The tritium activity concentration of air humidity is primarily determined by the amount of humidity itself. Therefore the concentration is directly linked to the seasons. Only significant changes in the specific tritium activity concentration can be detected by the use of the tritium activity concentration. Seasonal variations within the tritium activity concentration of hydrogen could not be observed. The values vary around 10 mBq/m3.
Sonnblick Observatory