3. What are the technologies used in the proposed security scanners?
Four types of security scanners have currently been developed for airport security use:
- X-ray backscatter scanners expose the subject to low energy X-rays. This low energy radiation passes through clothing but any dense object will reflect it back towards the source. Detectors measure this radiation and make an image of the subject’s body and any objects under the clothing. Usually the person is scanned twice, once from the front and then from the back, and a single scan lasts up to 8 seconds.
- X-ray transmission units use X-rays with significantly higher energies so that they pass directly through the person being examined. The image produced is similar to a medical X-ray and shows any concealed items that are sufficiently dense, even if the person has swallowed them or inserted them in a body cavity. Some units can operate in either a “low dose” or a “medium dose” mode, and a single scan takes from 5 to 15 seconds.
- Scanners that don’t use ionising radiation are being developed and there are two main types:
- Active scanners work in the same way as X-ray backscatter units but use radio waves instead of X-rays. During a scan, the individual is exposed to an electromagnetic field for up to 2 s. These units don’t produce any heating of body tissues but there is some uncertainty about the long-term effects of extremely low frequency and radiofrequency fields.
- Passive systems detect the very low levels of non-ionising radiation that are naturally emitted from the body or concealed objects. These systems produce no radiation of any type.
X-ray units are fitted with safety systems so the controls are password protected. Warning lights show clearly whether X-rays are being emitted or not and there are emergency stop buttons. Interlocks are fitted so that X-rays are cut off if a panel is removed for maintenance or if there is a fault in the machine. Finally, lead shielding is fitted around the machine so that radiation doses outside the scanning area are very low. More...