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Originally published March 25, 2011 at 10:03 PM | Page modified March 26, 2011 at 6:15 PM

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The small world of big nuclear worries

Traces of radioactive material from Japan's troubled reactors continue to waft around the globe, tracked by a network of sniffers so sensitive they put the best bloodhounds to shame.

Seattle Times science reporter

Tracking radiation

• An animation from Austria's Central Institute for Meteorology and Geodynamics tracks the spread of radiation from Japan's crippled nuclear reactors: www.zamg.ac.at/pict/aktuell/20110325_Reanalyse-I131-Period2.gif

• EPA radiation measurements: www.epa.gov/radiation

• Washington state Department of Health radiation measurements: www.doh.wa.gov/topics/japan/monitor-history.htm

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Traces of radioactive material from Japan's troubled reactors continue to waft around the globe, tracked by a network of sniffers so sensitive they put the best bloodhounds to shame.

Based largely on technology developed at Pacific Northwest National Laboratory (PNNL) in Richland, the instruments were designed to detect clandestine nuclear tests.

Japan's disaster proves they work just as well to trace fallout from nuclear accidents and help estimate total radiation releases and exposures.

Two weeks after the earthquake and tsunami that set off the nuclear crisis, dilute tendrils of radiation have spread across most of the Northern Hemisphere.

Outside of Japan, where officials on Friday widened the evacuation zone around the reactors, the amounts of radioactive material blown by the wind are very unlikely to pose health risks, said Edwin Lyman, of the Union of Concerned Scientists, a nuclear watchdog group.

Even if concerns that surfaced Friday about a possible containment breach in one of the reactors prove true, the chances of significant health effects to people 5,000 miles across the Pacific are low, he said.

A PNNL scientist estimates the levels of radioactive material from Japan that have made it to Washington represent exposures 18,000 times lower than the average daily dose from background sources of radiation, such as rocks and cosmic rays.

Midweek, instruments on PNNL's Richland campus detected wisps of radioactive iodine and cesium so minute they almost defy visualization — but PNNL physicist Harry Miley gave it a shot: Picture 260 Olympic-sized swimming pools filled with BBs, each representing an atom of air, he suggested.

The amount of cesium-137 picked up by the detectors would add up to 50 BBs. The airborne concentration of iodine-131 would account for one.

The levels of radioactive material from Japan have been dropping throughout the week, according to the Washington state Department of Health.

"It's kind of a blessing and curse to be able to detect this stuff at orders of magnitudes below where we would expect any health effects," said Kathryn Higley, head of Oregon State University's Department of Nuclear Engineering and Radiation Health. "It can scare the crap out of people when there's really no need to be concerned."

Very sensitive

The fact that the isotopes from Japan can be picked out halfway around the globe is a testament to more than a decade of research by scientists at PNNL and elsewhere.

"Our stations are 100 times more sensitive than any other equipment out there," said Lassina Zerbo, chief scientist for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), the Vienna-based United Nations branch that operates the ultrasensitive network.

PNNL maintains two of the instruments on its Richland campus, though they are not formally part of CTBTO's worldwide network of 60 detectors. PNNL is sharing its data with state and federal health agencies, which operate networks of less-sensitive detectors.

About 20 of the 124 sensors in the U.S. Environmental Protection Agency's monitoring network nationwide were not working when the quake hit, The Associated Press reported Friday.

Despite all the measurements, including those by U.S. aircraft and mobile sensors deployed to Japan, information reaching the public about the amount of radioactive material released remains spotty and confusing. The Japanese government and the utility company that operates the reactors have appeared reluctant to share data with the public.

Working backward from CTBTO's monitoring data and wind patterns since the quake, scientists in Austria estimated that releases of radioactive material from the Japanese plants are approaching those from the 1986 Chernobyl nuclear accident in Ukraine.

But the spread of dangerous contamination is much less extensive because there has been no Chernobyl-like explosion to propel material into fast-moving air currents high in the atmosphere.

An ideal indicator

The first hint of radioactive material from Japan to hit the contiguous United States came on March 16, at PNNL's xenon detector in Richland. Xenon-133 is an ideal indicator if you're trying to catch nations stealthily conducting underground nuclear-weapons tests, said Tony Peurrung, PNNL associate director.

The gas seeps out and travels long distances unchanged. But it took scientists 10 years to fine-tune methods to extract a few atoms of radioactive xenon from vast haystacks of air, he said.

The technology they came up with takes advantage of xenon's propensity to stick to cold surfaces, by passing air over charcoal chilled to nearly minus-200 degrees.

Another instrument detects the parade of radioactive isotopes, called fission products, produced in a nuclear blast or reactor. Iodine and cesium are among the most worrisome for human health. It was iodine-131 contamination that rendered Tokyo's drinking water unfit for babies this week.

Cesium-137 is one of the contaminants that has shown up in seawater off the Japanese coast, leading people to stop eating fish.

With a half life of eight days, iodine-131 diminishes quickly. But cesium-137 has a half life of 30 years, which means some of the most heavily contaminated areas in Japan may be off-limits for decades, said Lyman, of the Union of Concerned Scientists.

The state Department of Health and the U.S. Environmental Protection Agency (EPA) post daily radiation measurements, but folks trying to make sense of the numbers can face an apples-and-oranges conundrum.

The numbers reflect measurements of radioactive material in the air. But neither agency translates those readings into potential radiation exposures to people.

That's because dose or exposure calculations are complex. They factor in such things as body weight, respiration rate and whether radioactive material is likely to be inhaled or swallowed, said PNNL health physicist Dan Strom.

By making some basic assumptions for an average adult, Strom estimates that the levels of iodine-131 and cesium-137 detected in Richland would cumulatively deliver a dose of about .0005 microsieverts per day.

The daily dose from background radiation is about 8.5 microsieverts per day — or 17,000 times higher, he said. A chest X-ray delivers 100 microsieverts.

Within 10 miles of the Japanese nuclear complex, dose rates up to 2,700 microsieverts per day were reported Thursday.

EPA standards say a member of the public should be exposed to no more than 1,000 microsieverts of radiation a year from man-made sources.

Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com

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