If you’re one of those people who sit up at night, worrying about what radiation is doing to you, you might be worried about the new airport scanners described in the adjacent article. After all, those things probably throw off a lot of radiation, right?

Actually, according to their manufacturers, they are pretty harmless, relatively speaking.
Each scanner uses a different kind of radiation to scan your body. The milimetre wave scanner uses non-ionizing electromagnetic radiation, the same relatively harmless radiation that constitutes light. The backscatter X-ray scanner uses ionizing radiation, which can be dangerous in large doses.

While non-ionizing radiation doesn’t have enough energy to alter the chemical elements in your body, ionizing radiation can knock electrons off of atoms, creating ions. This kind of radiation can damage cells and DNA.

The average American receives 3.6 microsieverts (ms) of ionizing radiation a year, 80 per cent of which is from natural sources, such as cosmic rays, radon gas from the ground, — yes, the Earth is trying to irradiate you! — and radioactive elements in rocks and soil. The remaining 20 per cent is from artificial sources.

What follows is a list of common sources of ionizing radiation sources, and the amount of radiation absorbed from these sources.

• One backscatter x-ray scan: 0.00017
  ms*
• Wearing an LCD wristwatch: 0.0006
  ms/year
• Fallout from nuclear weapons tests:
  0.01 ms/year
• 1,600 km of commercial air travel:
  (approximately 2 hours of flight)
  0.01 ms
• Watching television: 0.01 ms/year
• Cosmic radiation, living at sea
  level: 0.24 ms/year
• Medical x-ray: 0.4 ms
• Food and water: 0.4 ms/year
• Radon gas: 2 ms/year

*Calculated from American Science and Engineering’s statement that one backscatter X-ray scan is equivalent to two minutes of flight at 9,150 metres.