The continuing threat from terrorists smuggling bombs on board aircraft has led to the installation and testing of body scanning equipment at airports.
Generally there are two main types of body scanner being tested in the UK and abroad: backscatter x-ray scanners (also called soft x-ray scanners) which give a very low dose of ionising radiation, and terahertz scanners which use radio wave frequencies which can penetrate clothing.
The backscatter x-ray scanners give a radiation dose but it is very low. It is comparable to one hour of natural background radiation and is considerably lower than the dose received from cosmic rays when flying at 35,000ft. The same radiation dose would be received in about 1 minute at this altitude.
In more detail, the dose from an airport backscatter x-ray scanner can be about 0.02 - 0.03 microsieverts per scan. Allowing for two or three scans per examination, this is about the same as people receive from natural background radiation in an hour (0.1 microsieverts). Also the cosmic ray dose received in a plane at 35,000ft is about 5 microsieverts per hour. This means an air passenger flying at 35,000ft receives in about 1 minute the same level of dose as delivered by the scanner.
On average people living in the UK receive about 2,700 microsieverts of ionising radiation from all sources in a year. This is primarily from natural and medical sources.
Terahertz scanners do not use x-rays so there is no comparable radiation dose.
Scientists at the Health Protection Agency have carried out an assessment of doses from a particular type of backscatter x-ray equipment for the Department of Transport (DfT). This type of equipment is being used for body scanning at some UK airports.
For more details, see the report on the DfT website Assessment of comparative ionising radiation doses from the use of rapiscan secure 1000 x-ray backscatter security scanner [external link]