Introduction to Naturally Occuring Radioactivity
Written and developed by Prof. Tor Bjørnstad (IFE/UiO)
Our world is radioactive and has been since it was created. Over 60 radionuclides (radioactive elements) can be found in nature, and they can be placed in three general categories:
- Primordial - from before the creation of the Earth
- Cosmogenic - formed as a result of cosmic ray interactions
- Human produced - enhanced or formed due to human actions (minor amounts compared to natural)
Radionuclides are found naturally in air, water and soil. They are even found in us, being that we are products of our environment. Every day, we ingest and inhale radionuclides in our air and food and the water. Natural radioactivity is common in the rocks and soil that makes up our planet, in water and oceans, and in our building materials and homes. There is nowhere on Earth that you cannot find Natural Radioactivity.
Radioactive elements are often called radionuclides, just nuclides or incorrectly radioactive isotopes. There are over 2000 different radioactive nuclides. Often, radionuclides are symbolized based on the element and on the atomic weight, as in the case of radioactive hydrogen or tritium with an atomic weight of 3 is shown as H-3 or 3H where the latter is preferred in the present course text. As another example, Uranium with the atomic weight of 235 would be shortened to U-235 or 235U.