Forest fires remobilize fallout from bomb tests

A sensitive instrument installed in the Canadian Arctic to monitor fallout from modern nuclear tests has detected small amounts of radioactive cesium produced by bomb tests decades ago. The material, which during the Cold War was spread across northern latitudes by high-altitude winds, is still being redistributed far and wide by forest fires, researchers say.

Scientists use a worldwide network of sensors to ensure compliance with the 1996 Comprehensive Nuclear-Test-Ban Treaty. While some devices are on the lookout for the telltale seismic vibrations generated by nuclear tests, others sniff the air for radioactive fallout ...The researchers aren't sure how the radioactive element makes its way from fallout-tainted soil into the atmosphere. Cesium, a chemical relative of potassium, is readily taken up by plants, so ash derived from wood and leaves could contain traces of the element. Another possibility is that because cesium has a boiling point of 670?C, some of the radioactive atoms may be vaporized from the ground by fires and then condense on airborne ash and soot, says Wotawa.

The cesium-137 lofted during a forest fire is diffusely distributed. "This isn't a health risk, but it's interesting," Wotawa notes. Scientists will have to account for the presence of wildfires when they're interpreting the readings from radiation sniffers, he says. - sciencenews