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From the source to the dosimetric impact assessment

The sources of radioactivity

​Radioactive elements have always been naturally present on Earth. The use of radioactivity for medical, industrial and military applications has generated the production of artificial radionuclides.

Published on 17 March 2015
Natural and artificial origins

Radioactivity has been naturally present in the environment since the formation of the Earth. In the atmosphere, radiation of cosmic origin interacts with certain elements to generate radionuclides such as carbon-14, beryllium-7, sodium-22, and tritium.

Examples of primordial radionuclides and their half-lives
uranium-235: 704 million years
uranium-238: 4.47 billion years
thorium-232: 14.1 billion years
potassium-40: 1.2 billion years

The Earth’s crust contains only about twenty radioactive elements, still present since the formation of the Earth due to their very long radioactive half-lives. These so-called “primordial” radionuclides decay into a stable element, in the case of potassium-40, or in a series of radioactive daughters, in the case of the uranium-235 and -238 families and thorium-232. The radiation emitted during the decay of these radionuclides thus has a terrestrial origin.

Uranium-238 decay series


Medical and industrial applications

​Since the beginning of the 20th century, radioactivity has been used in various industries and in medicine. These human activities have involved natural radionuclides and/or are the source of artificial radionuclides.   

Medical applications concern three fields:

  • diagnostic radiology and interventional imaging
  • nuclear medicine
  • radiotherapy
Positron emission tomography (PET) Photo credit: PF.Grosjean/CEA 

Industrial applications are very diverse. While some are well known (e.g. electricity production), others are more confidential. Examples include:

  • non-destructive testing of numerous industrial manufacturing processes,
  • irradiation to sterilize foodstuffs, medical devices, etc.
  • controlling of parameters (paper-thickness gauges, well logging, etc.)
  • eliminating static electricity
  • using unsealed sources as tracers
  • particle accelerators