There is much controversy
surrounding the advanced screening procedures that are employed by the
Transportation Security Agency. Much of this surrounds the new “Backscatter
X-Ray technology” which involves the use of a large machine to scan the entire
body for more things than can be seen on an actual X-ray machine or metal
detector. This technology is being used in response to increased attempts to
hide explosives on the person, including those used by the would-be underwear bomber
Umar Farouk Abdulmutallab, who attempted to ignite explosive hidden in his
underwear on a flight from Amsterdam to Detroit.
I have not had the experience of
going through said scanners (although I am always curious to see when it will
be my turn to be racially profiled in such a regard), but I have always been
intrigued by how x-rays are used to create an image that looks nothing like a “conventional
x-ray”. I saw some scanners in the new international terminal at Atlanta’s
Hartsfield-Jackson International Airport, and I was very intrigued by how these
devices work. Now, this isn’t something one brings up when going through
security, so I figured “Why not write a blog post about it?” This is especially interesting to me in the context of this being so radically different from how we described the elemental analysis characterized by XRF, while using the same basic principles.
The Abdulmutallab example is
just one example of how metal detectors are insufficient to detect many other
dangers. As our detection systems become more advanced, the chemistry and
physics of explosions as well as loopholes in our detection methods are even
further exploited by extremists to cleverly sneak past detection. It would
appear that science needs to proceed further to protect us from this threat,
and give us another tool to ensure that we can use the safest and most reliable
form of transportation we have while maintaining a sense of security.
Science’s answer is the backscatter
x-ray scanner. You may know them as the big machines behind the metal detectors
in most major American airports. This method is different than normal x-rays, which
send X-ray radiation through your flesh and into a film, being reflected only
in the bones, and from dual-energy transmission X-rays, which are used to
measure differences in density to allow for objects to be differentiated in our
carry-on bags (like my Rick Steves book, for instance). Instead, this is at a
much lower energy, and can only really penetrate your clothing and a part of
your skin. Then, your body reflects the rays back to sensors, which collect the
data and provide it to a TSA official.
The
photons of X-ray radiation bounce off tissues different than other items (such
as handguns or weapons). It can also pick up things the metal detector missed,
such as ceramic. The difference in the intensity of the scattering is what causes
the differences to be noticeable, combined with the changes in ionization of atoms the photons come into contact with and
speed of the photons.
Barring
the obvious privacy implications, there are questions about whether this is even
safe. X-rays are ionizing radiation, after all. Isn’t it scary to think that
there are photons being shot at your body that might ionize certain molecules?
Apparently, the TSA begs to differ, claiming that the radiation you receive
from the scanner is equal to roughly 60 seconds of cosmic radiation you
experience in-flight. Radiation is everywhere, apparently. Also,
millimeter-wave technology may be used, which uses microwaves instead of X-rays
(these are actually the ones that they use in Atlanta, not the backscatter ones
as I first thought). For those unfamiliar with the spectrum of light, that is
on the opposite end of the spectrum, and extremely low energy (second only to radio
waves, and let’s face it, if you’re afraid of those…then living on this planet
may not be a good plan.)
There
are a lot of visceral fears about radiation, but it is something we experience
throughout our entire lives. There was once an episode of “House” where they
took a Geiger counter to a patient’s house to measure radiation levels, and
remarked that everything electronic has some radiation (the Geiger counter measured radiation from outlets, lightswitches, everything! That cell phone you
keep in your pocket? That laptop you put on your lap? Yup, sources of radiation.
Radiation is ubiquitous (such as from cosmic radiation!). A little bit of backscatter X-ray radiation, or even
this new microwave concept that’s supposed to be safer, can keep the public
safe and at a mediocre risk to our health, if any, from current indications. I
am happy to know that science (and especially a cool part of photochemistry)
are being used for such good in the world. It is also exciting to see such techniques as those used for the study of art applied in a context that is so far removed from art.
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