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 abo
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Is Radioactivity Everywhere?
I am now almost certain that we need more radiation for better health. John Cameron 1922–2005
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. Natural radioactivity from the environment has three components: • cosmic rays, • terrestrial radiation (from the Earth’s crust), • incorporation (eating, drinking, and breathing). Radiation from these three sources usually affects all parts of the body equally, but a significant exception comes from the inhalation of the radioactive noble gas radon which represents a more localised exposure for the lungs. In addition to these natural sources, there are the exposures due to technical, scientific and medical installations developed by modern society.
© Springer International Publishing Switzerland 2016 C. Grupen and M. Rodgers, Radioactivity and Radiation, DOI 10.1007/978-3-319-42330-2_6
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6 Is Radioactivity Everywhere?
6.1 Cosmic Rays Cosmic rays are particles coming from space that strike the Earth. Our galaxy is the dominant source of high-energy cosmic rays. The lower-energy particles, which are the majority, predominantly originate from our Sun. Cosmic rays consist largely of protons (about 85 %) and helium nuclei (about 12 %). Only 3 % are nuclei heavier than helium. Nevertheless, all the elements of the periodic table occur as particles in cosmic rays. High-energy electrons are present in cosmic rays, but in much smaller numbers (about 1 %). Photons, in this case γ and X rays, are also incident on the atmosphere in large numbers (for historical reasons, these are not usually thought of as cosmic rays, although they interact in a similar way). Neutrinos, mostly coming from the Sun, enter the atmosphere in extremely large numbers, but effectively play no role in radiation exposures because they very rarely interact with normal matter. Cosmic rays interact with normal atoms (or, more precisely, with atomic nuclei) of gas in the atmosphere and produce a lar
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