The physics and biology of the TSA's backscatter security scanners

[salvorhardin]

This is a thorough, and lengthy, article covering the issue of radiation safety and TSA backscatter imaging scanners. I've included a couple of excerpts from the body and conclusion of the article, but I really recommend reading the whole thing because it's quite well done.

The primary downside of this technology is that it's ionizing radiation by definition—it wouldn't work if electrons weren't popped free from atoms. And that poses a health risk, since the resulting ions can be rather energetic, and undergo chemical reactions, either internally within an ionized molecule or with another substance in their environment. Damage to DNA from ionizing radiation is a known cancer risk, and steps are generally taken to minimize this.

But we're all exposed to ionizing radiation every day, since there's a constant flux that originates in everything from small quantities of radioisotopes in every-day items to cosmic rays arriving from space (both of which act much like medical X-rays in terms of their ability to pass through objects). The body scanners have been measured as producing a three microREM dose of radiation; a typical cross-country flight will produce exposures over a thousand times higher, and a chest X-ray is 10 times higher again than the flight. But, because of the differences between those sorts of exposures and the backscatter dose, it's not clear whether the same risk analysis applies to both...

In general, we find it difficult to disagree with the UCSF researchers. Although there is extensive safety data regarding exposure to X-rays, the backscatter scanners distribute the energy over the human body differently. As a result, the safety data we have may not be directly relevant. There's little reason not to generate additional data that is relevant. We now have very sophisticated assays that enable us to detect the sort of cellular damage caused by ionizing radiation, and decades worth of historic data on lab animals exposed to radiation. Providing some more definitive information than we have now should be relatively straightforward.

As we wait for that data, the TSA could go a long way towards reassuring passengers that they aren't at risk from something more threatening than the tiny dose of radiation delivered by a properly functioning scanner: the risk that the scanner won't be functioning properly. A detailed description of the procedures that are used to ensure their appropriate operation would go a long way towards establishing public confidence. And, if operations and testing procedures aren't in place, then the TSA is grossly overdue in formulating some.

Full article: http://arstechnica.com/science/news/2010/12/the-physics-and-biology-of-the-tsas-backscatter-security-scanners.ars