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19 March 2004

Have you been zapped today?

Forrest M. Mims III

Everyone knows that x-rays and radioactive materials are potentially dangerous. That's why the dentist places a lead apron over you and hides behind a shield when he pushes the button that sends a burst of x-rays through your teeth.

While it's essential to be cautious about radioactive rays and particles, it's also important to know that dozens of rays and particles are flying through your body at this very moment. If you've managed to survive this invisible onslaught, read on and I'll tell you more.

An electronic instrument called a Geiger counter counts radioactive rays and particles. Inside the instrument is a special tube about the size of your little finger. The Geiger counter counts each time a radioactive ray or particle flies through this tube.

In and around my office and house, a typical Geiger counter records 11 or so radioactive particles each minute. Around half those particles are cosmic rays from somewhere in outer space. The other half come from ordinary stuff like rocks, soil and some of the materials in our house.

Some of the phosphorus in your bones is slightly radioactive. So are many ceramics and some of the dust that collects on the screens of TV sets and computer monitors. Even newspapers emit an infinitesimal bit of radiation. But please don't stop reading your local paper, because newsprint is much less radioactive than your favorite magazine or even the bones in your arms.

Several years ago a couple of bored scientists with time on their hands created a stir with a note in Nature, the prestigious British science journal. They wrote that the clay used to coat the paper used to print scientific journals and magazines is slightly radioactive.

Maybe so, but so are plenty of other everyday things. So I sent a note to Nature titled "In defense of radioactive journals," which they promptly published. My note pointed out that overzealous regulators might try to ban all those radioactive scientific journals. Therefore journals should warn their readers about other radioactive activities--like flying in commercial aircraft.

The same Geiger counter that counts around 11 counts per minute at sea level will indicate from 300 to 400 counts per minutes in a plane 35,000 feet overhead. So scientists worried about radiation, I concluded, should avoid reading magazines while flying.

Instead, I suggested, they should relax and take a Geiger counter on their flights. It's entertaining to watch the count rise as the airplane does. But if you try this, be sure to switch the Geiger counter's speaker off. Otherwise, as I've learned more than once, you'll alarm nearby passengers.

Because high level nuclear radiation is dangerous, nuclear power plants have a bad reputation. Yet few people realize that coal is radioactive. One study found that the air and soil around power plants that burn coal, while safe, is much more radioactive than the air and soil around nuclear power plants.

Camping lanterns use lamp mantles that were once made with thorium, which is fairly radioactive. My son Eric and I used to do lots of science experiments together. One slow day we took a Geiger counter to a hardware store and thrust it inside a big display of lantern mantles. The familiar clicking of the Geiger counter became a loud buzz that attracted customers and the store's manager. They jumped back real fast when we told them that all those mantles were pretty radioactive.

While trying to maintain our composure, we explained that thorium lamp mantles are reasonably safe. But it's wise to avoid carrying them in a pocket or to touch or inhale their ash. This demonstration exercise no longer works since most lamp mantels are now made from safe, non-radioactive materials.

Forrest M. Mims III and his science are featured online at http://www.forrestmims.org/.

This feature was originally published in Forrest Mims's weekly science column in the Seguin Gazette-Enterprise, Seguin, Texas. The column is written for a general audience.