Annual Dose from Natural Radiation Sources in the Environment
(in areas of normal background radiation)

  Annual effective dose (micro-sievert)
Source External Internal Total
Cosmic rays 380   380
Cosmogenic radionuclides   12 12
Terrestial radionuclides      
130 170 300
Uranium-238 series:
238U to 234U to Thorium-230
140 1  
  4 1400
Radon-222 to Polonium-214
Lead-210 to Polonium-210
Thorium-232 series
190 80 270

Total (rounded) 840 1520 2400

Long Term Committed Doses from Man-Made Sources

Source Main radionuclides Collective effective
dose (man-Sv)

Atmospheric nuclear testing Carbon-14 Caesium-137 Strontium-90 Zirconium-95 30 000 000
Chernobyl accident Caesium-137 Caesium-134 Iodine-131 600 000
Nuclear power production Carbon-14 Radon-222 400 000
Radioisotope production and use Carbon-14 80 000
Nuclear weapons fabrication Caesium-137 Ruthenium-106 Zirconium-95 60 000
Kyshtym accident Cerium-144 Zirconium-95 Strontium-90 2 500
Satellite re-entries Plutonium-238 Plutonium-239 Caesium-137 2 100
Windscale accident Iodine-131 Polonium-210 Caesium-137 2 000
Other accidents Caesium-137 Xenon-133 Cobalt-60 Iridium-192 300
Underground nuclear testing Iodine-131 200

Most significant releases of radionuclides to the environment from human activities have been from atmospheric nuclear weapons testing. Next in importance is the Chernobyl accident, followed by long-term exposures from carbon-14 and radon-222 associated with nuclear power production. A large part (86%) of the collective dose from nuclear weapons testing is due to long-term exposure from carbon-14. Some perspective on these estimated doses from human activities can be gained by comparison with those from natural sources. An estimated 13,000,000 man-sievert due to natural sources (e.g., cosmic rays, potassium-40 in the body, and radon gas) is delivered each year to the world population (2400 micro-sievert x 5.4 x 109 persons).