The measurement of low concentrations of Kr-85 in atmospheric air samples.

Krypton-85 atmospheric contamination produced by the nuclear industry has been investigated on the basis of regular measurements. 85Kr concentrations observed in ground-level air of Prague between 1983 and 1993 are presented and their time-related changes analyzed. The long-term trend of 85Kr activity increased steadily over the monitored period with the growth rate of 38 mBq.m-3 (STP)/yr and reached about 1.2 Bq.m-3 (STP) in 1992. Short-term variations of the baseline level with the average amplitude of 12% show a seasonal periodicity. Occasionally detected extreme values of up to 2.5 Bq.m-3 (STP) indicate undispersed emissions from distant nuclear fuel reprocessing plants.