As Fukushima fallout circles the globe, nuclear sleuths sift it for clues

Three weeks into the nuclear crisis in Japan, minute traces of radioactive dust have circled the globe, even arriving in Maryland and Virginia.

Fallout from the Fukushima Daiichi nuclear plant has landed on 30 exquisitely sensitive detectors on desolate Arctic islands, on the tops of tall buildings and in other windy locales across the Northern Hemisphere, according to the Comprehensive Test Ban Treaty Organization, which maintains those sensors. Sniffing the air like silent sentinels, the 63 shack-like stations (with 17 more planned) are capturing tiny radioactive particles in filters much like those on a home furnace.

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Japan's prime minister sounds a resolute note, promising to win the battle against an overheating nuclear plant even as atomic safety officials raised questions about the accuracy of radiation measurements at the complex. (April 1)

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Japan’s nuclear emergency

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• Japan pressed to expand evacuation zone; new safety questions for workers at plant
• As Fukushima fallout circles the globe, nuclear sleuths sift it for clues

Analysis of that dust is a key step in an intricate process of nuclear sleuthing: The dust’s distinctive chemical signature can show scientists whether the particles blew into the air from a bomb, a damaged nuclear reactor or used uranium fuel. It can even point to the extent of damage suffered by a fission reactor. Tracing global wind patterns back then pinpoints where the emissions originated.

“It’s nuclear forensics,” said Kai Vetter, a professor of nuclear engineering at the University of California at Berkeley, who built his own radiation detector atop a campus building after the Fukushima crisis began.

“You can learn quite a lot from the pattern of radioactive isotopes,” said Hamish Robertson, a physicist at the University of Washington in Seattle.

In the United States, another network of more than 100 stations maintained by the Environmental Protection Agency is also gathering radioactivity from Japan. State health departments maintain their own monitoring systems, which is how Maryland detected tiny traces in the air and water March 24.

Super-sensitive detection

After the March 11 earthquake and tsunami damaged Fukushima, the global sensor network began to light up for the first time since nuclear detonations in North Korea in 2006 and 2009.

On March 14, a station on the Kamchatka Peninsula in Russia sniffed out unusual radioactive elements. That cloud then split, drifting southward and eastward, with one arm arriving two days later in Sacramento, and three days after that in Charlottesville. On March 20, the ultra-thin broth of radioactive particles blew over Iceland. And it reached all the way to Kuwait City on March 25, two weeks after the first emissions from Fukushima.

The reporting of even these minuscule amounts of unusual radiation has caused alarm, driving a run on potassium iodide pills and Geiger counters. But officials at the EPA and the Centers for Disease Control and Prevention and independent experts have repeatedly stressed that the amount of radioactivity detected outside Japan is far too low to affect human health.

Modern radiation detection systems are simply astoundingly sensitive, they explain, designed to pick up traces of nuclear explosions anywhere in the world. The detector atop the CTBTO’s headquarters in Vienna, Austria, still catches vestiges of the Chernobyl disaster that occurred 25 years ago, said Lassina Zerbo, director of the group’s international data center.