Sources of radiation

We are all continuously exposed to ionizing radiation. The most important sources of background radiation include the soil, rocks, cosmic radiation, and radiation from naturally radioactive substances in our food. The human body also contains naturally occurring radioactive substances.

We ingest radioactive substances with food, drinking water or when breathing air. Uranium and thorium and their decay products naturally occurring in the base rock also migrate into the body. The best known of these decay products is radon, which belongs to the decay chain of uranium.

Radiation doses

The radiation dose describes the health hazard caused by radiation. Radiation causes two types of health hazards, direct and random. Cancer is an example of a random effect of radiation.In Finland, the average annual radiation dose per person is approximately 3.2 millisieverts (mSv). More than half of this is caused by radon present in indoor air. Another 30 percent of the dose comes from natural background radiation, and 15 percent from the use of healthcare appliances.The potassium-40 isotope, which occurs in bones, is the source of an absorbed dose of approximately 0.2 mSv. The Chernobyl nuclear power plant disaster in 1986 resulted in radioactive emissions that also reached Finland. The average dose from the Chernobyl fallout is less than one percent of the annual dose in Finland.A radiation dose from the emissions of a nuclear power plant can be calculated at approximately 0.0002 mSv per year. The limit for the radiation dose arising from the operation of a nuclear power plant has been set at 0.1 mSv in Finland. The same limit also applies to the final disposal of spent nuclear fuel.Examples of radiation doses:
  • 0.01 millisieverts (mSv): the dose imposed on the patient by a single dental X-ray examination
  • 0.1 mSv: the dose imposed on the patient by a single X-ray examination of the lungs
  • 2 mSv: the cosmic radiation dose incurred by a person working onboard an airplane in one year
  • 3.7 mSv: the average annual radiation dose of a person living in Finland (from indoor radon, x-ray examinations, etc.)
  • 20 mSv: a single CAT scan
  • 50 mSv: the maximum allowed five-year dose for a radiation worker
  • 6,000 mSv: the dose that may be fatal if incurred within 24 hours