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This is the international symbol for radiation. It is often used to indicate that radioactive materials are stored nearby.
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Radioactive

Some materials give off radiation. We say that those substances are "radioactive". Radioactive materials are often, though not always, hazardous to living things.

There are many different types of radioactive materials. Some emit particle radiation, like alpha or beta particles or neutron radiation. Some give off electromagnetic radiation, such as gamma rays or X-rays.

Most elements come in various "versions", called isotopes, with different numbers of neutrons and slightly differing properties. In many cases, less-common isotopes of common substances are radioactive. For example, the rare isotope of carbon called carbon-14 is radioactive. It has 8 neutrons (instead of the usual 6) and radiates beta particles. When they emit radiation, radioactive substances undergo radioactive decay. The element may be transformed from one isotope to another, or may become a different element altogether. When carbon-14 decays by emitting a beta particle, it becomes nitrogen-14. Isotopes that do not decay are said to be "stable".

Radioactive isotopes can be dangerous to living things and damaging to equipment such as electronics. The level of danger depends, however, on the amount of radioactive substance present and the type of radiation and the rate of decay. Radioactive materials exist (mostly in trace quantities) in nature all around us. Small enough doses of most types of radiation cause us little harm.

Humans make use of radioactive materials in many ways. We use them in medicine to "label" and detect certain substances or tissues. We use them to determine the ages of artifacts via radiocarbon (carbon-14) dating. We also use them for nuclear power and in nuclear weapons.

Last modified August 26, 2009 by Randy Russell.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA