Backscatter body scanning is an X-ray-based technology that yields a high-resolution image of a person's body beneath their clothing to reveal concealed objects. The process involved is sometimes referred to as "backscatting." Backscatter devices have been used for several years in prisons, diamond mines, and customs searches, and are used in some airports as an alternative to metal-detection and pat-downs for security.
In a backscatter portal, a single ray is passed rapidly over a person's body, taking just eight seconds to scan each side. Data collected from the position of scattered photons are processed to deliver a photographic-quality image. The process uses high-energy X-rays, which tend to reflect (scatter back) from objects, unlike the low-energy X-rays used for medical procedures, which tend to penetrate objects. Because of an effect called "Compton scattering," the rays are deflected differently depending on the density of the matter being scanned. They penetrate clothing but not flesh and are blocked more completely by solid objects. This effect means that most weapons will be sharply revealed by backscatter imaging. However, some critics of the devices claim that because the X-rays used in backscatter devices do not penetrate skin, the devices could be foiled by people with certain physical characteristics, such as overlapping body parts, that make it possible for them to hide an object on their naked bodies.
According to Robert Jacksta, Director of Passenger Programs at U.S. Customs, the amount of radiation emitted by one of the scanners is roughly equivalent to the exposure experienced by a passenger on a two-hour flight. Although relatively insignificant on an occasional basis, that level of exposure could be a concern for people who travel frequently and/or are subjected to radiation exposure from other sources.
There are a number of other concerns about backscatting, not least among them the issue of privacy. The technology has been referred to as a "virtual strip search" and is sometimes likened to the "X-ray Specs" advertised in comic books in the 1950s and '60s. A major difference between the two is that, unlike the eyeglasses that disappointed so many of that generation, backscatting actually works as advertised.