illuminating science

When this came up over dinner on the weekend, I was sure it was another example of an urban legend, or at least miscommunication, and I was keen to get into Uni and debunk it. But to my utmost surprise, it’s actually real, legitimate and may be part of our lives before too long. What am I talking about? Basically, X-Ray vision for use in airport security!

Normal X-rays, like a doctor takes, work by shooting a blast of X-rays (a form of light with a much shorter wavelength than ordinary, visible light - hence much more powerful) at your body, and looking at what comes out the other side. Your bones block out more of the X-rays than do your soft tissues, and so we can see the structure inside your body. It’s exactly like shining a torch through paper, say, and looking at the shadow you get out the other side. Back in the old days, X-ray machines were even used in shoe shops to measure your foot size - kids loved looking at the bones in their feet! Unfortunately, this fell out of fashion when it was realised that large doses of X-rays can cause cancer.

These days, our techniques are more refined, so we use smaller doses and get better resolution to boot, giving us virtually no chance of getting cancer from the number of X-rays we have in our life. Of course, a doctor who might take 20 or more x-rays a day always leaves the room - just in case the odds catch up with them.

Anyway, I digress. But the most interesting refinement recently is a technique called backscatter x-ray, where instead of looking at the shadow the X-rays make, we look at the X-rays that are reflected. By using only small doses of X-rays, we can get very little backscattering of soft material - like clothes - but lots of backscattering off hard things, like metal, plastic - and skin. The result is a new technology for airports that basically creates a “naked image” of you - removes your clothes, and reveals any hidden objects like knives or explosives that you might have concealed on your person. The downside is that without your clothes, the images don’t leave a lot to the imagination - you really are naked, albeit in a black-and-white, kind of blurry sense. There’s conflicting information about whether the image will actually be stored, but I can’t see any benefit in doing so. In the U.S., the system has been banned until the designers can come up with a way of masking out the, er, interesting bits from the image.

I’m not sure quite how I feel about it - if the images are deleted immediately, then no-one but the screener will see them. And in many ways, it’s far less intrusive than a medical examination - particularly a mammogram or a pap smear if you’re a woman! But there we’re talking about necessary, medical procedures, conducted by trained professionals. Security guards don’t really fill me with the same sense of…security.

Beyond airports, though, there’s talk of using this to scan trucks for illegal immigrants, contraband and drugs. Check out some sample pics - the technology is pretty amazing!

My final (honestly!) comment is simply that this kind of technique really does give some credence to Superman’s X-ray vision. Sure, we’re not going to see full colour pictures, but maybe we can someday get close! So you nay-sayers who said Superman was just fiction, there you go!

For more information, check out stories here and here.