Make your own Geiger counter

In the nuclear age, a radiation detector, and an app to run it are within your reach
Julia McKinnell
Make your own Geiger counter
Photograph by Liz Sullivan; Nick Veasey/Getty Images

Take one empty box of Frisk mints, some aluminum foil or a copper coin, eight photodiodes and free assembly instructions. Power it up with a nine-volt battery and a new app from a group of concerned scientists and engineers, and you’ve got yourself a Geiger counter.

Radiation Watch is a Japanese non-profit organization formed by volunteers in the wake of the tsunami that caused the meltdown at the Fukushima Daiichi nuclear power plant a year ago. Its mission is to make information about radiation levels as cheap and easy as knowing the time. The group’s YouTube video shows a woman with a cellphone, with a toddler on her lap: “A mother has no way of knowing for sure whether the park nearby is safe for her child to play in,” says the voiceover. After Fukushima, hand-held Geiger counters were too expensive for most people to buy while cheaper models sold out.

Atley Jonas, a Lethbridge, Alta.-born ex-pat living in Yamanashi, bought a Geiger counter kit and the iPhone app, the Pocket Geiger Counter Pro, as a “sanity check,” he said in an email. “As you know, official sources haven’t always been forthcoming with information, and the accuracy has also been disputed.” Jonas takes his Geiger counter to public parks and the woods; he’s also taken it to Tokyo, about 200 km south of Fukushima, where radiation levels were higher than home.

“I don’t think people realize how much radiation is around,” says British-born engineer Clive Maxfield, author of Bebop to the Boolean Boogie: An Unconventional Guide to Electronics. Maxfield lives in Huntsville, Ala., about 10 km from the Browns Ferry Nuclear Power Plant. “By a strange quirk of fate,” he said in an interview, “my best friend from when I was 16 onwards was near Chernobyl when Chernobyl went off, and he died a few years ago of brain cancer.”

Maxfield paid about $40 for a DIY kit he bought from Amazon that he runs with the $6.99 Pocket Geiger Counter Pro. “I was watching one of those end-of-the-world programs on Discovery Channel [about] 10 ways in which the world might end by Wednesday lunch. Just after that was the disaster in Japan. I thought, hang on a minute. There’s this nuclear power plant just down the road. I thought if it started going off, how would I ever know?”

A personal Geiger counter has practical uses, too. When a friend sent him a pair of old marbles made from uranium glass, Maxfield’s dosimeter detected unsafe levels of radiation. The next week, he blogged: “I have radioactive balls!” It can also detect the presence of deadly radon gas in a house.

The homemade Geiger counter, housed in the empty mint box, uses eight cheap semiconductors called PIN photodiodes to detect radioactive beta particles and gamma rays, and aluminum foil or a copper coin to create a shield to block naturally occurring background radiation. The app does the calculations, and the mobile device (it works with the iPad and iPod Touch) emits clicks. The more radiation, the faster it clicks.

The Pocket Geiger Counter Pro uses GPS (the free Lite version comes without mapping). “The app will log your position and log the amount of radioactivity,” Maxfield explains. “Say you’re a farmer. You could walk around your fields and go, ‘Good grief! The corner of this field is highly radioactive. I better not eat those tomatoes!’ ”

But make sure you buy the real thing, warns Maxfield. “The spoof app looks like the radioactive symbol and it’s got a meter and numbers and things.” It’s not a real Geiger counter but it does make clicking noises. Fake Geiger is “really handy for tricking your 17-year-old son,” says Maxfield. “You move it around, and as you move it toward his bowl of Corn Flakes, it starts clicking furiously and he drops his spoon in alarm.”

Maxfield’s Geiger counter sits on his desk at home. “I find it strangely comforting because when it’s clicking now and then, you know there’s nothing wrong. If it started click-click-click-clicking, I’d be looking around to see if a friend was playing a trick on me. If not, I’d be calling my wife and grabbing our son, and heading for the hills.”