The Science of Backscatter X-rays

November 19, 2010

Brit Trogen

Most of the recent controversy around the TSA involves the use of backscatter x-rays in airports; a technology that allows them to capture images of nude bodies. Privacy issues aside, should you be concerned about the backscatter scanners?

For starters, they aren't the same as regular X-rays. In a dual-energy X-ray scanner, like the kind you send your luggage through, a single X-ray beam composed of high energy photons is fired at the object in question. Soft matter usually lets the beam pass right through, where it’s picked up by detectors on the other side, while harder matter like bone doesn't.

Backscatter X-ray scanners, however, generate images based on how X-rays are scattered by particular elements like carbon or hydrogen. These scanners are designed to differentiate types of organic matter, since elements with lower atomic numbers tend to scatter very efficiently. Still, X-rays are hitting your body to produce the image.


Science in Seconds Brit Trogen

So what's the risk of radiation? Here's where the science gets a little more fuzzy. Estimates from the manufacturers range between 0.005 and 0.009 millirems of radiation per scan, while the “safe” limit per year is 25 mrem from a single source. This means it would take about 280 scans per year to max out (in comparison, flying for three hours will dose you with about 1 millirem from cosmic radiation). But according to others, the risk is a little higher.


David Brenner of Columbia University believes that the radiation dose won't be distributed evenly along the body, with the skin on your scalp retaining up to twenty times the radiation dose quoted. This would put it at a much higher risk of basal cell carcinoma; a common form of cancer associated with X-ray exposure. 


Does this mean you should opt out? That depends... How do you feel about pat downs?


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