Our Radioactive Planet
Everyone receives radiation exposure from the radioactive elements in the Earth's crust and from the natural radioactivity originating in deep space. These natural sources are responsible for most of the radiation dose all human receive during their lifetimes. This and subsequent pages will describe in detail the role played by the natural radioactive elements in the earth's crust. Since they are found in the food we eat, the water we drink, and the air we breathe, it also follows that they are to be found in our bodies.
Since we live on a radioactive planet we radioactive inhabitants of this planet ought to have some knowledge of the kind of radioactive elements that make up our surroundings, and in particular, our bodies.
The major sources of radiation are the long-lived terrestrial (primordial) radionuclides and the radionuclides produced during their radioactive decay. Primordial radionuclides are those radioactive nuclides with long half lives; half lives so long that there has not been sufficient time for them to completely decay since they were incorporated into our planet when it was formed. These radionuclides belong principally to three decay chains - the uranium, thorium and actinium series - and are present in low concentrations in our soil and water.
There are other primordial radionuclides, such as 40K and 87Rb, and also cosmogenic radionuclides, that are produced in the atmosphere by the collisions of cosmic rays, primarily neutrons, with atmospheric argon, oxygen and nitrogen. The cosmogenic radio-nuclides of most interest include are 14C and 3H (tritium).
None of these radio-elements are present within human bodies in large quantities, particularly if we think in terms of mass, but if we think in terms of radioactive disintegrations per second, the results may surprise you.
potassium, 40K, produces the most radioactive decays within the
A discussion about this potassium and it's radioactive isotope is
A discussion about this potassium and it's radioactive isotope is available.
The rates of decay for the most active radioisotopes in the human body have been tabulated and are listed on an additional page.