Backscatter x-ray technology is extensively used for airport security purposes. Originally introduced by Dr. Steven W. Smith in 1992 mostly as commercial devices, backscatter scanners detect radiation that bounces off the surface of the body and create its image with the x-rays.
Advanced imaging technology can strip-off passengers to detect objects or materials such as weapons, guns, knives, liquid explosives or drugs that are possibly strapped on the body. With former airport security technology such objects might be undetected because metal detectors or conventional x-ray machines could not see through clothes. Any material showing up as unusual object on the human body may be associated to explosives or weaponry.
American Science & Engineering (AS&E), the manufacturer of backscatter scanners, bases its system on scatter X-ray photons, known as Compton scattering. Compton scattering produces high quality photo-like x-ray images by discriminating materials to organic or low-numbered based on their ranking on the periodic table. Elements with higher atomic numbers on the periodic table (e.g. metals) scatter X-ray photons less strongly. Elements with lower atomic numbers on the periodic table (e.g. carbon, hydrogen, lithium) scatter X-ray photons very strongly. Because explosives, drugs, cigarettes, and human body have low atomic numbers, the backscatter scanner can filter and process their elements absorbing their scatter patterns and producing a 2D gray scaled image of the body.
Captured images from backscatter x-ray scanners resemble a lot to normal scanned photos, but are clearer and easier to interpret than conventional X-ray images that are often fuzzy and unclear.
The major advantage of backscatter x-ray technology is that it can interpret a suspect material that has been identified by airport security officials and take it for inspection before it becomes a threat. In doing so, air passengers are protected from aspiring terrorists.
Moreover, the radiation levels are much lower than those of medical x-rays because backscatter scanners operate at much lower energy levels. Air passengers are exposed to significantly less radiation than when submitted to a medical x-ray. Besides, the radiation does not penetrate the skin because backscatter technology can scan the human tissue without having to go through the skin to produce the body image.
On the other hand, there has been a lot of discussion as to whether backscatter technology should be used. Privacy concerns are raised mainly by privacy campaigners who claim that backscatter scanners are a major threat to child protection laws. First of all, children should not be scanned at the airport for not being exposed to radiation at all. However, the images of children who are scanned are so explicit they amount to "virtual strip-searching" facilitating child pornography offenders wearing the uniform of Transportation Security Administration (TSA).