We encounter radiation each day from a variety of sources. The average American is exposed to about 6 millisieverts (mSv) of radiation annually, according to the United States Nuclear Regulatory Commission (USNRC). Half of this typically comes from background radiation that occurs naturally in the environment, and half comes from medical tests, such as X-rays, mammograms, and CT scans.
According to Kelly Classic, MS, spokesperson for the Health Physics Society, sources of environmental radiation include:
Radioactive compounds in soil and building materials like concrete, brick, and stone
Radiation from outer space that your encounter when you fly on airplanes or visit high-altitude places
The mineral potassium in your own body (a small fraction of potassium, which our bodies need to function, is radioactive)
Radon gas in the home, which accounts for about 2 mSv of exposure each year, and is the largest contributor of background radiation
Finally, there's the kind of radiation released during nuclear reactions, such as what's disseminating from Japan's Fukushima Daiichi plant.
Here's a look at various sources of radiation exposure (dose of radiation in millisieverts (mSv)), according to data from the Health Physics Society and the U.S. Environmental Protection Agency (EPA). By way of comparison, a single dose of radiation below 0.01 mSv is considered negligible by the National Council on Radiation Protection and Measurements.
Banana: 0.0001
Dental X-ray: 0.005
Living within 50 miles of a nuclear power plant: 0.01 (per year)
A flight from New York to Los Angeles: 0.04
Smoking 1 ½ packs of cigarettes: 0.08
Chest X-ray: 0.1
Living at sea level: 0.25 (per year)
Mammogram: 0.3
Living in Denver: 0.5 (per year)
Abdominal CT scan: 14
Measures between reactors No. 3 and No. 4 during the March 15 explosion at the Fukushima plant: As high as 400 per hour
