Over the Thanksgiving weekend, the "opt-out day" meme died in a cacophony of self-satisfied headlines. That conversation appeared to focus less on assessing the safety of X-ray backscatter devices and more on the invasiveness of the Transportation Security Administration's security procedures. So it seems that a blog post by Jason Bell, a molecular biology and biophysics PhD candidate in Steve Kowalczykowski's lab at UC Davis, may still be relevant. Referencing a letter by four UC San Francisco faculty, he wrote early last week:
In order to really understand these concerns, I think its important to consider the type of radiation used in these scanners, which the TSA has described as 'soft' and 'safe'. First, we need to clarify the definition of 'soft' vs 'hard' X-rays. The TSA has been stating that the X-rays used in the back scatter machines use 'soft' X-rays, which are defined as radiation between 0.12-12 keV (or kilo electron volts) and are generally stopped, or absorbed, by soft tissue or low density matter. 'Hard' X-rays are between 12-128 keV and are absorbed by dense matter like bone. According to the TSA safety documents, AIT uses an 50 keV source that emits a broad spectra. . . .Essentially, this means that the X-ray source used in the Rapiscan system is the same as those used for mammograms and some dental X-rays, and uses BOTH 'soft' and 'hard' X-rays. It's very disturbing that the TSA has been misleading on this point. Here is the real catch: the softer the X-ray, the more its absorbed by the body, and the higher the biologically relevant dose! This means, that this radiation is potentially worse than an a higher energy medical chest X-ray.
Previously: Health concerns over whole body X-ray scanners