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 (see adjacent graph from here). 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. Its 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.
If that doesn’t scare you, here’s some more food for thought.
[E]ven though the dose may actually be low, these machines are capable of much higher radiation output through device failure or both unauthorized or authorized reconfiguration of either hardware or software. Which brings me to how the scanner works. Essentially, it appears that an X-ray beam is rastered across the body, which highlights the importance of one of the specific concerns raised by the UCSF scientists… what happens if the machine fails, or gets stuck, during a raster. How much radiation would a person’s eye, hand, testicle, stomach, etc be exposed to during such a failure. What is the failure rate of these machines? What is the failure rate in an operational environment? Who services the machine? What is the decay rate of the filter? What is the decay rate of the shielding material? What is the variability in the power of the X-ray source during the manufacturing process? This last question may seem trivial; however, the Johns Hopkins Applied Physics Laboratory noted significant differences in their test models, which were supposed to be precisely up to spec. Its also interesting to note that the Johns Hopkins Applied Physics Laboratory criticized other reports from NIST (the National Institute of Standards and Technology) and a group called Medical and Health Physics Consulting for testing the machine while one of the two X-ray sources was disabled (citations at the bottom of the page).
So not only are they capable of being reconfigured to higher output of radiation, but the testing was also inconsistent, and the test scanners were not of the same quality claimed in the specifications. Bell continues by pointing out a major flaw with the TSA documentation on these scanners — a lack of proper credits and expertise.
These questions have not been answered to any satisfaction and the UCSF scientists, all esteemed in their fields and members of the National Academy of Sciences have been dismissed based on a couple of reports seemingly hastily put together by mid-level government technicians or engineers. The documents that I have reviewed thus far either have NO AUTHOR CREDITS or are NOT authored by anyone with either a Ph.D. or a M.D., raising serious concerns of the extent of the expertise of the individuals and organizations evaluating these machines with respect to biological safety. Yet, the FDA and TSA continue to dismiss some of the most talented scientists in the country…
And what of the employees who need to run the scanners?
At the high end, if for example a TSO is standing at the entrance of the scanner when it is running at maximum capacity, then that officer could hit their radiation exposure limit in as few as 20 working days (assuming an 8 hour shift). While we may not be very happy with our TSOs at the moment as the face of these policies, we need to keep in mind that they really should be wearing radiation badges in order to know their specific exposure (especially for those officers who may also have to receive radiation exposure for medical reasons).
The conclusion remains the same.
As far as I’m concerned, the jury is still out on whether these machines are safe or even could be made safe for this application. Until then, I suggest keeping your family out of these machines and as vile as it is, either submit to a physical search or just don’t fly.
This is an excellent, well-written review with much more information. Read it all and stay informed. Be sure to read the referenced TSA information as well and note that several safety reports were conducted with some of the scanner functionality disabled thereby negating the validity of the results.