The word “radiation” has negative connotations, even though radiation itself is ubiquitous and essentially a foundation of life; radiation from the sun is the energy source that powers plants and supports global ecosystems. Even so, some forms of radiation can be deadly, and a key distinction is ionizing vs. non-ionizing radiation.
Ionizing radiation is found in radio waves, microwave ovens, infrared light, visible light and some ultraviolet light. It can move atoms in a molecule around or cause them to vibrate (EPA, 2011).
Ionzing radiation is generally what people think of when “radiation” is mentioned. Ionizing radiation is higher energy and can strip (usually) electrons orbiting the nucleus of an atom (see image below, from Princeton University Environmental Health and Safety module). In effect, an electron is given enough energy to leave the atom and forms two charged particles, and results in a transfer of energy into the surrounding area. Examples of ionizing radiation are X-rays, and cosmic rays. The energy released from one ionization is capable of disrupting the chemical bond between two carbon bonds. Important molecules in the body such as DNA contain carbon bonds, thus ionizing radiation can damage these molecules.
United States Environmental Protection Agency. 2011. Ionizing and Non-Ionizing Radiation. Last updated March 11, 2011. Accessed on March 31, 2012 from http://www.epa.gov/radiation/understand/ionize_nonionize.html
Moeller D. Environmental Health. 2011. 4th edition. Harvard University Press, Cambridge, Massachusetts, USA.
Princeton University. Environmental Health and Safety. Open Source Radiation Training. Module 1: Radiation Properties. Last updated September 26, 2008. Accessed on March 31, 2012 from http://web.princeton.edu/sites/ehs/osradtraining/radiationproperties/radiationproperties.htm