STUK detected radioactive cesium in the air in Helsinki—sheltering required only in case of a million-fold concentration
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. The amount of cesium in the air was not high enough to have an effect on human health.
Tarja K. Ikäheimonen, head of STUK’s Environmental Radiation Surveillance and Emergency Preparedness department, reminds that artificial radioactive substances are detected in the samples of STUK’s air samplers regularly every year. The regularly detected cesium 137 usually originates from the fallout of the Chernobyl nuclear power plant accident that occurred in 1986.
Director Ikäheimonen points out that while the detected radioactivity does not pose a threat, its amount is exceptionally high. This is why it cannot derive from the Chernobyl fallout. The fact that the sample contains only cesium 137 also rules out any possibility of it deriving from a nuclear reactor emission.
“The measuring result, 4,000 microbecqurels per cubic metre of air, is about a thousand-fold compared to normal,” says director Ikäheimonen. She also reminds us that, in this case, an amount a thousand-fold compared to normal means that the concentration is roughly a millionth of a concentration that would require people to shield themselves from it.
While the source of the radioactive cesium detected by STUK is currently unknown, it is under investigation. STUK monitors the levels of radioactive substances in outdoor air at eight localities: Helsinki, Kotka, Imatra, Kuopio, Kajaani, Rovaniemi, Sodankylä and Ivalo. Only the samples from Helsinki have been measured so far with regard to the aforementioned dates. The passage route of the radioactive substance will become clearer after the measurements. On Thursday, and Friday, the air currents to Helsinki came from the east and southeast.
The automated network gives a warning if the level of radiation rises above normal levels.
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.
The measurement data concerning radioactive substances in outdoor air are available on STUK’s website.
For further information, please contact:
Director Tarja K. Ikäheimonen, tel. +358 9 759 88 596,
Information Officer Risto Isaksson, tel. +358 9 759 88 208