A trace of radioactive cobalt detected in the air in Imatra

The particle sample collected in Imatra between 9 and 16 March 2026 contained radioactive isotopes of cobalt, Co‑60. The activity concentration was very low, 0.3 microbecquerels per cubic metre of air.

The origin of such very small amounts of artificial radioactive substances is often impossible to determine. This time as well, the source is unknown. The cobalt may have travelled to Finland from far away. However, nothing indicates that the cobalt would originate from a major release that could cause problems even near the emission source.

Radioactive cobalt is generated, among other things, in nuclear power plants during operation, and it can be released into the air for example during maintenance work.

The Imatra sample also contained a small amount of radioactive cesium (Cs‑137), which is still present in Finland’s environment because of the Chernobyl nuclear power plant accident. The amount of cesium in the sample corresponds to the levels normally observed in samples collected in Imatra.

STUK has collection stations in eight locations in Finland to monitor the concentration of radioactive substances in the air. The collectors at these stations draw in large volumes of air, causing airborne particles to accumulate on their filters. The filters can then be analysed to measure the activity of radioactive substances and determine which substances are present. The method allows detection of even extremely small concentrations.