Whole Body Scanners
Whole Body Scanners
Over the last few years, prisons and other security sensitive areas have began using a device that scans the whole body for contraband. The scan produces an imagine of the skin, and will show objects like guns, drugs, other weapons under clothing. This procedure is often used an alternative to whole body strip searches. The device uses a low energy x-ray or gamma source to produce the image.
The draw backs to this are 1) privacy issues; 2) radiation dose to the individual; 3) radiation dose to the workers. The privacy issues are beyond the scope of this site, but lets look at the radiation dose issues closer.
These devices operate on a physical process called backscatter. Backscatter uses X-rays that reflect away ("scatter back") from the low-Z material (skin, clothing) but not most high-Z material (metal). Backscatter then makes "reflections" that define the high-Z materials as separate and distinct images from low Z.
The amount of radiation a person receives is called dose, and is normally measured in mrem or uSv. The average person in the US gets about 360 mrem per year from background sources. So, that is about 1 mrem per day (average). The backscatter scanners will give a scanned person a few urem, or less than 2% of one day's background radiation dose. From a risk stand point, this is insignificant, compared to other risks we encounter every day. For more on background radiation and risk, see our page on Radiation and Us and for more on terms, see our page on terminology.
Recently, there has been a lot of talk about pilots and their doses from the backscatter units. This is good that the discussions is going on, but let's take a look at this process a little bit more. A backscatter scan will produce a small amount of x-ray dose is true. And the dose is additive, so getting 10 scans would mean 10X the x-ray dose. What is being missed in the current talks is 10 times a very small amount is still, a very small amount. Flying at cruising altitude will cause the people on a plane to receive about 1 mrem (rough rough number) for every 1000 miles flown due to natural background radiation (i.e. cosmic radiation). So, for a trip coast to coast, all onboard the plane will get about 3 mrem. To get 3 mrem from the backscatter scans would mean having 150 scans!!!! So, let's keep in perspective... the backscatter scans will not significantly increase the pilot's radiation dose, even for a working lifetime, in comparison to their natural background dose.
Also see the AS&E web site and the line of Rapiscan personal monitors. Other interesting articles include Wikipedia Backscatter Scanners , How Stuff Works and a Q&A from the Health Physics Society or a HPS paper on the topic.
The FDA has a site full of information, and another site "Very Low Health Risks from Full-Body X-ray Scanners"