Understanding radiation exposure.
In the days after an 8.9-magnitude earthquake rocked Japan on March 11, the world's attention turned to the state of the Fukushima Daiichi nuclear power plant. For the first time since Chernobyl, the mainstream media has been talking seriously about radiation levels. Here are a few basics to help you put the relative risks of radiation exposure into perspective.
First, when we talk about human radiation exposure, we're specifically discussing "ionizing radiation." This is high-energy radiation that's powerful enough to break or modify chemical bonds, and cause tissue and chromosome damage in the human body.
While many of the sources of radiation in our lives produce lower-energy, or "non-ionizing radiation" (such as microwaves and radio waves), we're also exposed to very low levels of ionizing radiation every day. That's why, when calculating risk, experts talk about exposures above "background levels." These include radiation doses from environmental radon, as well as cosmic radiation reaching Earth from space.
Here's a short list that shows how selected radiation exposures compare.
Radiation Source mrem * Traveling 1,000 miles by plane 1 (one time) Natural cosmic radiation at sea level 24 (annual) Natural cosmic radiation in Denver 50 (annual) Environmental radon 200 (annual) Average total exposure of U.S. resident 620 (annual) Natural background sources 310 (annual) Medical procedures & consumer products 310 (annual) CT scan (head and body) 1,100 (one time) Limit for U.S. nuclear workers 5,000 (annual) Japan's limit for nuclear workers 25,000 (annual) Radiation levels measured near Fukushima evacuation zone 1,600 (annual) Peak radiation inside damaged Fukushima reactor 40,000 (per hour) For more information, go to www.epa.gov/radiation. You'll also find a helpful visual depiction of the various exposures at xkcd.com/radiation. * Radiation exposure to humans is often measured by a unit known as "roentgen equivalent man," or rem. A millirem (mrem) is 1/1000th of a rem. Sources: Agence France Presse, Scientific American, U.S. Department of Energy, U.S. Environmental Protection Agency, U.S. Nuclear Regulatory Commission, Wall Street Journal
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|Title Annotation:||GREEN GAZETTE|
|Author:||Phelps, Megan E.|
|Publication:||Mother Earth News|
|Date:||Aug 1, 2011|
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