Physicists Detect Low-level Radioactivity From Japan Arriving İn Seattle

University of Washington physicists are detecting radioactivity from Japanese nuclear reactors that have been in crisis since a mammoth March 11 earthquake, but the levels are far below what would pose a threat to human health. On March 16, the scientists began testing air filters on the ventilation intake for the Physics-Astronomy Building on the UW campus, looking for evidence of dust particles containing radioactivity produced in nuclear fission.

The first positive results came from filters that were in place from noon on March 17 to 2 p.m. on March 18. Readings peaked three days later and then dropped, but have risen slightly since then.

"It's a faint signal. You have to filter a lot of air to see it," said Michael Miller, a UW research associate professor of physics. "We've definitely seen it fluctuate up and down, and we are correlating those peaks and drops with any changes in normal background radiation levels."

The measurements were begun because of concerns about effects of radioactivity on very sensitive physics experiments. They also document that radioactivity in airborne particles arriving in the United States is well within safety limits, said R.G. Hamish Robertson, a UW physics professor and director of the Center for Experimental Nuclear Physics and Astrophysics.

Using the air filters allowed sampling of 10 times more air than in methods used previously and proved to be a key in successfully detecting larger dust particles that had attracted radioactivity from the Japanese nuclear plants, Robertson said.