|By Jon Shende||
|December 30, 2010 06:15 AM EST||
As stated in Part 1 my focus on this article will be more on the backscatter technology as this seems to be where traveler scanning is heading and it involves ionizing radiation. Currently we have varied opinions on this technology with a major concern for the routine use of ionizing X-rays being that of health issues.
Also mentioned was the fact that our skin being our largest organ, it may be affected from backscatter skin surface scans in the long term. Continuing on as stated earlier, per Wikipedia , there are three companies manufacturing commercial backscatter X-ray devices:
American Science and Engineering with their Smartcheck
Rapiscan Systems with their Secure 1000 
Tek84 with their AIT84 Body Scanner & Castscope 
According to data on the Smartcheck  page the effective x-ray dose measured using the companies patented z-backscatter system is less than 10 µRem per scan where a µRem is 1 millionth of a Rem. From the above EPA table, 5 Rem is suggested as a level for adult safety. So in theory the radiation impact on us is minimal.
Rapiscan via their Secure 1000 data-sheet also claims less than 10 µRem and Tek84's AIT84 with its Dual mode of operation (it incorporates both backscatter and transmission X-ray)  claims to be a next generation machine, this considering the fact that the Secure 1000 was invented almost two decades ago by the same person - Dr. Steven W Smith.
According to Dr Smith  there seems to be some misunderstanding between X-ray dose penetration and image penetration, which seems to be fuelling the varying schools of thought regarding backscatter technology and its effect on the human body.
After reading the document I still found no answer why I felt some soreness as described in Part 1, and although in theory his explanation seemed sound, I still strongly feel that there needs to be more data, and testing done to ensure the safety of this system.
Dose Penetration is a measurement of how deeply the energy from the x-ray beam is deposited into the body.
Imaging Penetration describes how deep into the body the acquired image can detect objects. 
As a security analyst I also question the total efficacy of these systems - I believe that they suit a purpose and can identify certain substances, however, those of you who profile and conduct counterterrorism exercises will know exactly where I am coming from when I question the total efficacy of these systems.
A paper  on hidden object identification by Tribe, Newnham,Taday and Kemp of TeraView Limited states:
It is unclear whether backscatter or millimeter wave imaging can provide spectroscopic substance identification. Thus, X-ray and millimeter wave portals are likely to prompt frequent further searching whenever an image indicates a suspect item or area.
The researchers proposed using an alternative system that taps into the radiation at terahertz frequencies. Terahertz frequencies according to them possesses unique properties that may be advantageous for security applications, as this spectrum not only penetrates many non-conducting materials, but is non-ionising unlike x-ray.
Such a system will also allow radar-like imaging in three dimensions, as well as a simultaneous collection of spectroscopic information. (With Spectroscopy specific signatures of varying chemicals can be identified).
This system will not only reduce the stress and aggravation with an airport scan, but will allow for increased efficiency in the screening process. Travelers need not remove their shoes -speeding up the line, more data can be collected with an improved overview for the screener. There will also be reduced anxiety on the part of travellers regarding the harmful effects of radiation.
Hidden object detection: security applications of terahertz technology;Terahertz and Gigahertz Electronics and Photonics III, edited by R. Jennifer Hwu, Proc. of SPIE Vol. 5354 (SPIE, Bellingham, WA, 2004)
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