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Answer to Question #8440 Submitted to "Ask the Experts"Category: Security Screening — Airport Screening The following question was answered by an expert in the appropriate field: Q
Would you please explain exactly how the new body scanners(x ray) work.
An article in our paper stated that the low-level x rays "penetrate clothing but not skin" and uses the "backscatter" to record the data. It just does not sound right or I have forgotten all my x-ray physics. Don't most low-level x rays get absorbed by the body or clothing? I would imagine that you would have to have quite a bit of low-level energy to get enough backscatter to record anything. I'm used to thinking of higher-level energies and the issues with the lower levels used in mammography. A good explanation of how and what intensity/quality x rays are used in these scanners would be helpful and how the image is recorded. I work in a catheterization laboratory as a registered technologist in radiography so I am sure my annual work exposure would make walking through one of these scanners inconsequential. Still, I would rather not add to my total. A
Thank you for your question. You are right, there is some radiation exposure absorbed by the body during these scans—about 0.005 mrem (mrem is a unit of effective radiation dose; daily background radiation is about 1 mrem). The idea behind the backscatter units is the energy spectrum of the scattered radiation as it is detected when the x rays scatter off of various substances including your body. Things containing organics (carbon, hydrogen), like drugs and explosives, scatter the x rays substantially while heavier elements will absorb the x rays more. Much like you see on the x rays you take—bone (more dense) absorbs more radiation while lung tissue (mostly air) scatters or allows them to pass through. The idea is pretty interesting, but the idea that these x rays "penetrate clothing and not skin" is pretty misleading. While there isn't much absorbed radiation in the body, there is some. The airplane flight, though, will expose you to a few mrem—much more than this backscatter system. Kelly Classic
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