The physicists and nuclear safety specialists measure risk using something called the “sievert” (previously, they used the “gray”). The sievert reflects an amount of radiation and allows comparison of relative risk, sort of like the U.S. dollar and international monetary policy. Sort of. Using the sievert, the risk for example of an airport scanner can be accurately and precisely compared to the risk of a chest X-ray or a CT scan or residence in Hiroshima in 1945. It is not confusing or misleading or complex. In fact, it is the simplest arithmetic imaginable.

The results are in on scanners and have been for a long while. They are available in countless places, including in today’s New York Times, Wikipedia’s section on exposure, the American College of Radiology website, and the government’s own websites (and here). Here are the facts: A routine chest X-ray gives between 100 and 1,000 times the radiation exposure of an airport scanner. Furthermore, the radiation exposure from a CT scan is 10 to 20 times that of a chest-X-ray and therefore thousands-fold more than a pass through an airport scanner. And annual mundane living on this earth with the various natural (and less natural) sources of radiation exposure constitutes the equivalent of 25 to 50 chest X-rays per year, or tens of thousands of times the dose of the airport scanner. In other words, folks, the airport scanner is not even sort of worrying.