Radioactive materials are becoming less and less radioactive. For example, consider the so-called. half-life. In the course of time, therefore, the total radioactivity in nature should decrease. But we still find uranium, for example. Now what “feeds” the radioactivity?
Answer
Dear Ton,
Radioactivity is a natural phenomenon that occurs when an unstable atomic nucleus changes to a more stable state with excess energy being emitted in the form of particles (alpha, beta, neutrons) or electromagnetic radiation (gamma).
Our earth’s crust contains some radionuclides, the so-called primordial radionuclides, which have a very long half-life. Examples include uranium-235 (half-life 7.038 × 108 years), uranium-238 (half-life 4.468×109 years), thorium-232 (half-life 1.405×1010 years) and potassium-40 (half-life 1.251×109 years).
Each of these radionuclides decays to a different nuclide which in most cases is also radioactive. We then speak of decay chains. The resulting daughter isotopes thus form a mix of radionuclides, each with a specific half-life, ranging from a few picoseconds to many millions of years. This explains the presence of natural radioactivity in our earth’s crust, and consequently also in our building materials, our food, our body,…
In theory, therefore, the total radioactivity in nature will decrease as a function of time, but this time span is very long compared to the time spans we use in everyday life.
Tom Clarijs
Scientific collaborator
Answered by
SCK CEN Academy for Nuclear Science and Technology
Boeretang 200, 2400 Mol
http://www.sckcen.be
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