Thursday, October 11, 2007

Radiation everywhere!

This morning, I was reading this news story on a new type of security scanner that is being tested for use in airports. I'm not going to comment on the discussions of privacy issues and airport security. But I'm blogging about it because I noticed a subtle error in the science that is a common misconception in the public. The quote in question states:

The new type of device being tested, called a "millimeter wave" machine, doesn't use radiation, Golden said Wednesday during a demonstration for reporters at the agency's headquarters in Arlington, Va. Instead, it uses electromagnetic waves to create an image based on energy reflected from the body.

The problem is with the word "radiation." When most people hear that word, they think of nuclear bombs, horrible illness, deformities, and other awful things. But, to a scientist, radiation is much, much more.

There are two main types of radiation that most of us experience: particle radiation and electromagnetic radiation. Particle radiation deals with subatomic particles, including protons, electrons, alpha particles (two protons and two neutrons joined together), muons (another subatomic particle), and many other such things. We are constantly being bombarded with most of these, and most are not dangerous in small amounts. Muons from cosmic rays are constantly passing through us; there is nothing we can do to stop these particles, but luckily most do no damage. Alpha particles come from certain types of radioactive decay; our skin easily stops those, and it takes a really high dosage to do harm a person. Electrons can come from radioactive decay, but electron radiation is also used in cathode ray tubes (the heart of a lot of TV sets and computer monitors). Electron radiation can do damage, but, again, you need to be close to the source to be in trouble.

Electromagnetic radiation is also a part of everyday life. We often call it "light." This radiation includes radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays. The list above is in terms of energy, from the weakest to the strongest. The dangerous radiation is all high energy -- gamma rays, X-rays, and ultraviolet light. These are energetic enough to damage our cells and our DNA, and so are best avoided. But small doses are okay (like a diagnostic X-ray), and even necessary (UV light is needed by your body to produce some vitamins).

On the other hand, radio waves and microwaves are very weak. So how does your home microwave cook food? The microwaves in there are tuned to specific frequencies (like tuning your radio), and at those frequencies water absorbs microwaves and turns them into heat. So, if you keep pumping those microwaves in to some water, the water will warm up. But if the microwaves aren't at the right frequencies, they'll just pass right through you without doing anything.

So, back to the news article. Note the quote says that the millimeter wave machine doesn't use radiation. WRONG! Millimeter waves are radiation! What the article should say is that the millimeter wave machine doesn't use harmful radiation, like an X-ray machine does. (However, even the X-ray machine uses such a low dose that the person being screened would not be harmed; it is the security people who might be in danger harm's way.)

The point is that radiation is not inherently bad. Radiation is just a physical process. The bad radiation is energetic radiation (X-rays, gamma rays, ultraviolet light, and certain types of particles). So, the next time you hear that something is emitting radiation, don't instantly get worried. Stop and think, is this harmful radiation? And, if not, you can breathe easier.

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