Case Study on the Use of X Ray Scanning of Airline Passengers for the Detection of Weapons. Annex I

The use of X ray scanning of airline passengers is carried out in some States and prohibited in others. However, there are no published regulatory decisions on formal justification of this type of practice. The matter was discussed at the Dublin Symposium and the information presented at that symposium forms the basis of the discussion here. The purpose of such X ray scanning is to detect any concealed weapon that might otherwise be carried onto an aeroplane. Such X ray scanners are seen as a complement to the use of walk-through metal detectors and pat-down searches. They are also an alternative to a more intrusive 'strip-search'. The equipment uses backscatter X ray imaging to quickly acquire high resolution images. To perform a scan, the subject is asked to stand relatively still on an external stage for several seconds while the system acquires two-dimensional raster-scanned image data. The electronic image of the subject is formed using the intensity of X rays scattered from each location on the body via Compton scattering interactions. The X ray scatter intensity is a function of both the atomic number and the density of the material probed by the primary X ray beam, in this case either the body itself or items on the body. Objects that are denser than body tissue, such as metals, explosives, plastics and packed drugs, interact more strongly and therefore appear on the image along with the body itself. Two scans (front and back) are typically required for a routine inspection. However, the technique only images materials on the surface of the body and is not effective for detecting materials that are concealed within body cavities