STUK supervises STUK supervises
STUK supervises

Deposition samples collected on a continuous basis

Deposition samples collected on a continuous basis

Deposition samples are collected using a device placed outdoors, specifically designed for this purpose. Samples are being collected on a continuous basis in eight localities around Finland. In addition, there are deposition collection stations in the vicinity of nuclear power plants.

The collection area is 0.05 or 0.07 square metres, and wet and dry depositions are not separated. In Helsinki, there is an extra device with a larger collection area that separates wet and dry depositions. The devices used in the vicinity of nuclear power plants are also large in area.

Some of the deposition collection stations are operated by the Defence Forces or the Finnish Meteorological Institute, and two stations are operated by the Frontier Guard. STUK collects samples in Helsinki and Rovaniemi, the cities where it is present.

In this context, deposition refers to radioactive materials that have fallen to the ground or water from air. Deposition may come with rain (wet deposition) or as dry deposition. Deposition samples are collected on a continuous basis, and they are usually analyzed monthly. 

If analyses of air samples or external radiation indicate signs of fresh fallout, deposition samples are collected at shorter intervals. This ensures that information on the composition of the fallout and the amount of radioactive substances in different localities is obtained promptly. The results also provide the basis for studies investigating the migration of radioactive materials in earth and water environments.

The annual totals of cesium-137 depositions in 2011 measured in different localities varied between 0.5 and 2.7 becquerels per square metre.

Annual deposition of cesium-137 in 2011 (becquerels per square metre) in different localities. The differences between localities are due to the uneven distribution of the Chernobyl fallout. Dust remigrates into the air from soil and falls down again, usually with rain, into the collector.