Posted in General Science on Nov 23, 2010
Yesterday I flew to San Francisco from New York’s JFK Airport (Terminal 8). As I was going through the TSA security checkpoint, I noticed that even though OSI’s Rapiscan Secure 1000 body scanners were in place, they were not used to screen the passengers. Relieved, I happily went through a regular metal detector.
Upon arrival at SFO, I glanced at the security checkpoint and I saw a different type of body scanner – L3′s ProVision. So it seems we have two competing advanced imaging technologies: OSI’s backscatter X-Ray or so-called the Compton Scattering Effect and L3′s “active millimeter wave radio frequency” (MMW). Here is what each manufacture says about their product’s technology and safety:
The Rapiscan Secure 1000’s patented technology is composed of an ultra low-dose X-ray source that images backscattered X-rays through to a remote operator’s workstation.
Emission Per Scan: Less than 10 microRem
Leveraging harmless radio waves, ProVision offers advanced imaging—without any health risks.
• The signals created by ProVision are 10,000 times lower than other commercial radio frequency devices.
• ProVision does not use X-rays or ionizing radiation.
Ok, it appears that OSI’s technology is patented and a quick search for all the US Patents assigned to “Rapiscan Systems, Inc” reveals 43 search results ( I used advanced “AN/Rapiscan” query in UPSTO Patent Full-Text and Image Database).
The very first patent 6,094,472 titled – “X-ray backscatter imaging system including moving body tracking assembly” was filed with the USPTO on 04/14/1998 by the inventor Dr. Steven W. Smith (Poway, CA).
As you can see from the drawing above, it doesn’t quite look like a Rapiscan Secure 1000 system, however, the patent does provide some clues to a radiation exposure level:
“at least one X-ray source comprises an X-ray tube operating at a potential of 70 KV at 10 ma.”
“Radiation exposure is an important consideration in X-ray concealed object detection systems. The United States National Council on Radiation Protection (NCRP), in NCRP Report No. 91, “Recommendations on Limits for Exposure to Ionizing Radiation”, 1987, addresses this issue. In this report, the NCRP states that a radiation exposure of less than 1000 microRem per year in excess of environmental levels is negligible, and efforts are not warranted at reducing the level further. Persons employed in high security or secured facilities, or those who frequently travel by airlines, may be subjected to many hundred security examinations per year. A yearly radiation exposure limit of 1000 microRem permits a single scan exposure within the range of 1 to 10 microRem for the general public. In accordance with the NCRP recommendations, radiation levels significantly higher than this present a non-trivial health risk.”
“the scan duration for a complete scan is on the order of 0.3 seconds”
Alright, it looks like I can go through Rapiscan Secure about 100 times per year and I should be ok, right? But then I found this recent article published in “Radiation Protection Dosimetry” where Rez et el.  examine radiation exposure of Compton backscatter X-rays. The researches caution:
“Although vendor-determined doses are small and not associated with adverse health effects, dose accuracy is in question because of inherent difficulties in measuring X-ray exposures from rapidly moving X-ray beams.”
Hmm, it is getting interesting, I will continue dig dipper.
 P. Rez, R.L. Metzger and K.L. Mossman, “THE DOSE FROM COMPTON BACKSCATTER SCREENING”, Radiat Prot Dosimetry, Nov. 2010.