Originally published Friday, March 18, 2011 at 1:57 PM

Radiation sensors pick up small traces here

Radiation stations have confirmed that tiny traces of radioactive material from the damaged Japanese nuclear reactors have reached Washington state.

By Sandi Doughton

Seattle Times science reporter

Radiation data online

EPA and the state Department of Health (DOH) are now posting radiation-monitoring data.

• Graphed results from West Coast monitoring stations, including the one in Seattle, at: www.epa.gov/radiation/rert/radnet-seattle-bg.html.

• The Washington DOH site also provides normal background levels for comparison: www.doh.wa.gov/Topics/japan/monitor.htm.

The posted data are for gross level of beta radiation, an overall measure of radioactive material in the air. None of the stations show any levels above background yet, including stations in Seattle, Tumwater and Spokane. Data from Richland are being compiled.

A network of sensitive radiation stations, designed to detect traces of radioactive isotopes from underground nuclear tests, has confirmed that radioactive material from the damaged Japanese nuclear reactors has reached the U.S. West Coast — including Washington.

The Environmental Protection Agency says radiation levels from the material are one-millionth of natural background levels.

Operated by the United Nations' Comprehensive Nuclear Test Ban Treaty Organization, the sensors detected xenon-133 gas in this state Wednesday and Thursday, the EPA reported. On Friday, a sensor in Sacramento, Calif., picked up similar levels.

Xenon-133 is produced by fission in nuclear reactors. It poses no health concern at the levels detected, according to an EPA statement.

"These types of readings remain consistent with our expectations since the onset of this tragedy, and are to be expected in the coming days," the statement said.

The test-ban organization shares its readings with the U.S. Department of Energy and other governments, but not with the public.

After the explosion of the Chernobyl plant in Ukraine in 1986, which hurled far more radioactive material into the atmosphere than the damaged Japanese reactors, air monitors in the United States also detected trace amounts of nuclear material. The radiation dose to Americans then was estimated at one-thousandth of the annual background exposure.

Background radiation levels vary with winds, atmospheric conditions and local soil types.

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

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