Where do radioactivity and ionizing radiation come from?

Due to different physical processes, radioactive materials produce ionizing radiation, which can influence humans and the environment. Ionizing radiation can be generated by natural or artificial radioactivity.


Natural radioactivity consists of two components – terrestrial and cosmic radiation.


Terrestrial radiation is produced by natural radio nuclides existing in the soil, like Thorium-232 or Uranium-238. The gaseous Radon-222, which results from the decay of Uranium-238, also provides an important contribution to the natural radiation exposure of humans.


Cosmic radiation results from radioactive nuclides which are formed when particles from the cosmos react with atoms from the earth’s atmosphere. Furthermore, high-level gamma radiation from the outer space reaches our planet. But before reaching the surface of the earth, it is damped by the air of the inner atmosphere. Our mighty earth’s atmosphere is therefore not only a source of radiation but also an effective protection against cosmic radiation.


Beside natural radioactivity humans are also exposed to artificial radioactivity.

Medical applications like X-ray or CT examinations contribute the biggest part of it. In addition, long-distance-flights at high altitudes increase the exposure, too. In contrast, the radiation exposure caused by emissions of radioactive particles or radiation from nuclear power plants is negligibly low.


The measure for the radiation exposure of humans is called "dose", one unit being 1 millisievert (mSv). Normally, this refers to the dose one person was exposed to during one calendar year.


The table shows the average annual radiation exposure of a person in Germany; however, individual values can differ considerably.
Dose caused by natural radioactivity  
terrestrial radiation 0.5 mSv/a
exposure to Radon-222 1.0 mSv/a
cosmic radiation 0.3 mSv/a
Total 1.8 mSv/a
Dose caused by artificial radioactivity  
medical applications 1.5 mSv/a
other applications 0.1 mSv/a
exposure to radiation from nuclear power plants < 0.01 mSv/a
Total 1.6 mSv/a
Total annual radiation exposure 3.4 mSv/a
Limit for persons occupationally exposed to radiation 20 mSv/a


You can get more information about radioactivity and radiation protection at and