Long-term investigations of radioactive matter in the air of Zagreb, Croatia

Investigations on the distribution and fate of naturally occurring, nuclear-weapons-produced, and reactor-released radionuclides in the city of Zagreb, Coatia, have been conducted as part of the monitoring program for radioactive contamination of the human environment in Croatia since the early 1960s. This paper describes long-term investigations of man-made 137Cs and naturally occurring 7Be in the city of Zagreb after the Chernobyl accident. The Chernobyl nuclear accident caused a major increase in 137Cs activity concentrations only in 1986, which quickly decreased over the next few years to pre-Chernobyl values. The observed mean residence time for 137Cs in the air during the post-Chernobyl period from January 1987 to December 1990 was estimated to be 1.0 year. During this period, the observed mean residence time for 137Cs in fallout was estimated to be 0.9 years. The mean 7Be activity concentration in the air from 1987 to 2004 was (5.4 ± 2.8) × 10 − 3 Bq m − 3 . The measured 7Be activity concentrations showed seasonal behavior with the highest usually measured in July. Despite the constant presence of radioactive matter in the Zagreb air during the observational period, activity concentration values never exceeded legal limits. Consequently, 137Cs doses incurred by inhaling contaminated air after the Chernobyl accident were very small.