Is Radioactivity Everywhere?
Many people believe that radioactivity is all man-made, whether it be made in laboratories, nuclear power plants or nuclear explosions. This is entirely wrong. Since the Earth formed, along with the formation of the Sun and the other planets and moons about 4.6 billion years ago, both it and everything on it have been radioactive to a certain extent. In the distant geological past, the Earth was even more radioactive than it is today. The Sun and the Earth were made from the debris of supernova explosions, in which all the elements of the periodic table, including radioactive isotopes, were created. We are actually made of (slightly radioactive) star dust. Radioactivity is a natural ingredient of all life forms and also of the air that we breathe and the food that we eat. In addition, we are constantly being bombarded by cosmic-ray particles which mainly come either from the Sun or from other sources within our galaxy. These particles constitute a low-level radiation exposure. In the following chapter, the different natural sources of radioactivity will be presented in detail and compared with additional man-made radioactivity.