engleski

Activity concentration of tritium (3H) in precipitation - long-term investigations performed in Croatia and Slovenia

Systematic studies of isotope composition of monthly precipitation in Croatia and Slovenia have been performed since 1976 and 1981, respectively. The monitoring included measurements of radioactive isotope of hydrogen – tritium (3H) as well as stable isotope ratios of hydrogen (2H/1H) and oxygen (18O/16O). Isotope data are partly available in the Global Network of Isotopes in Precipitation (GNIP) at https://nucleus.iaea.org/wiser. This work presents details on long-term monitoring of tritium activity concentration in precipitation at Zagreb, Croatia, and Ljubljana and Portorož, Slovenia, performed in collaboration between Ruđer Bošković Institute (RBI) and Jožef Stefan Institute (JSI). Sampling locations have been changed during the long-term monitoring. Local contamination with technogenic tritium was noticed at the RBI site and therefore precipitation has been collected at the Zagreb-Grič site at the Meteorological and Hydrological Service of Croatia, in the center of Zagreb since 1996. Monitoring in Ljubljana was performed between 1981 and 1993 at the synoptic station Ljubljana–Bežigrad located at the Hydrometeorological Survey of Slovenia (today Slovenian Environment Agency – ARSO), between 1993 and 2000 at the JSI (station Ljubljana–IJS), and finally, since 2000 at the Reactor Centre of the JSI (station Ljubljana–Reaktor) in the vicinity of Ljubljana. In addition, monitoring has been performed at the ARSO synoptic station Portorož airport since 2000. Zagreb and Ljubljana are both continental stations while Portorož represents a coastal station. The long-term data records showed tritium pattern typical of continental stations of the Northern Hemisphere. Seasonal variations were superposed on the basic decreasing trend of mean annual values until app. 1997. The maximal 3H activity concentration at station Zagreb was observed between May- July, mostly in June. A secondary maximum was also observed three times in January and February. The lowest 3H activity concentrations were almost uniformly distributed from October to February, with a slightly more frequent occurrence in December. The seasonal distribution at the Ljubljana station was characterized by the most frequent appearance of the maximum in July, no secondary winter maximum, and the minimum was most frequently measured in November, although it was distributed from October to March. The ratio of the maximum to minimum value for Zagreb and Ljubljana precipitation ranged from 2.2 to 5.7 and from 2.3 to 5.5, respectively, without a significant trend. Data recorded during last 2 decades, however, show almost constant mean annual 3H activity concentration ranging between 5 and 10 TU with the average of about 9 TU for the continental stations Ljubljana and Zagreb, while for the coastal station Portorož lower value of about 7 TU was observed. Seasonal variation remained with winter activities close to the natural pre-bomb 3H activity concentrations (≤5 TU), and summer values rarely above 20 TU.

tritium ; precipitation ; Slovenia ; Croatia

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