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November 29, 2010

Biochemist Raises Questions about Nude-o-Scopes [rdbrewer]

Jason Bell, a biochemist working in biophysics.


Chromosome Damage From Radiation

On the significance of the type of radiation used:

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.

(Emphasis mine.) He has several concerns about the power of the machines in question:

  • Based on the limited engineering schematics released in the safety documents, the machines could be easily reconfigured to perform through-the-body X-rays, and the hardware has the capability to output high doses of radiation though failure or both authorized and unauthorized reconfiguration of software and hardware.
  • The X-ray beam is being rastered across the body--that is, scanned in lines from side to side, top to bottom, like a TV screen. If the machine fails or gets stuck during a pass, there is a possibility a person's eye, testicle, or hand, for example, could receive a dangerous dose of X-rays.
  • This possibility gives rise to certain questions: 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?
  • Also, what is the variability in the power of the X-ray source during the manufacturing process? The Johns Hopkins Applied Physics Laboratory noted a significant disparity in their test models--which were supposed to be adjusted to exact specifications.

On the widely publicized claim that radiation from the machines amounts to the same exposure one would receive after two to three minutes of flight:

With respect to errors in the safety reports and/or misleading information about them, the statement that one scan is equivalent to 2-3 minutes of your flight is VERY misleading. Most cosmic radiation is composed of high energy particles that passes right through our body, the plane and even most of the earth itself without being absorbed or even detected. The spectrum that is dangerous is known as ionizing radiation and most of that is absorbed by the hull of the airplane. So relating non-absorbing cosmic radiation to tissue absorbing man-made radiation is simply misleading and wrong.

Much more at the link, including questions raised by scientists about the lack of testing and safety data provided by the government and/or the manufacturers and the lack of independent testing and data. He also points out how stingy the release of information has been, with many things redacted in the material that has been made available. Why?

Link via BoingBoing.


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posted by Open Blogger at 12:01 AM

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