STUK: No abnormal detection of cesium elsewhere in Finland, the concentration in Helsinki has normalised
The air sampler on the roof of the Radiation and Nuclear Safety Authority’s (STUK) building in Roihupelto, Helsinki, collected an exceptionally high amount of radioactive cesium 137 on the 3rd and 4th of March. “While the measurement data—4,000 microbecquerels per square metre of air—is about a thousand-fold compared to normal, it is nevertheless only a millionth of a concentration that would require people to shield themselves from it. The amount detected does not pose a threat to health,” says Tarja K. Ikäheimonen, Director of the Environmental Radiation Surveillance and Emergency Preparedness department at STUK.
“After the observation, we continued our investigation by measuring the filters of the air samplers at five other localities and concentrations of radioactivity recorded by the sampler in Helsinki on the 4th and 5th of March. Measuring radioactivity from the filters takes several hours, in some cases up to a full day,” says Ikäheimonen.
Nothing out of the ordinary was detected in the data from the air samplers in Imatra, Kuopio, Loviisa, Olkiluoto and Rovaniemi. On the 4th and 5th of March, the cesium 137 concentration of the sampler in Helsinki was 12 microbecquerels per cubic metre of air. “This means that the radiation level has dropped back to normal. We are nevertheless still very actively trying to find out the source of the temporary peak,” says Ikäheimonen.
“Although it is unlikely that the cesium 137 would have originated outside Finland, we cannot rule this possibility out altogether yet. We also know that it was not generated by a nuclear test or a reactor,” adds Ikäheimonen.
STUK also monitors outdoor radiation in Finland with the help of an automated radiation monitoring network composed of 255 monitoring stations. Rather than collecting samples from the air, these monitoring stations measure real-time environmental radiation directly. The monitoring stations give an immediate warning if the radiation level rises above the level of normal background radiation, which is 0.05–0.3 microsieverts per hour. The concentrations now detected by the particle sampler are so low that they are not observable even as a slight rise in normal background radiation in the outdoor air, due to which the automated monitoring network does not detect them.
Further information on the monitoring of radioactive substances in outdoor air and the measurement data concerning radioactive substances in outdoor air is available on STUK’s website.
Director Tarja K. Ikäheimonen, tel. +358 9 759 88 596
Head of Public Affairs Kaisa Raitio, tel. +358 9 759 88 795