First results of Fukushima radiation measurements in California


Measurements of leaked radiation from Japan's Fukushima nuclear disaster have found an unprecedented spike in radioactive sulfur in La Jolla, Calif., according to atmospheric chemists at the University of California, San Diego.

Still, the levels observed are not a concern for human health, says Mark Thiemens, the dean of the Division of Physical Sciences at UCSD.

Thiemens and his team found 1501 atoms of radioactive sulfur in sulfate particles per cubic meter of air over a four day period ending on March 28th, the highest ever seen in several years of observation at the site.

The team published its findings Aug. 15 in the online edition of Proceedings of the National Academy of Sciences, and said that its calculations "imply that approximately 0.7% of the total radioactive sulfate present at the marine boundary layer at Fukushima reached Southern California."

Japanese officials on March 12 ordered the Tokyo Electric Power Company to pump seawater to cool the reactors at Fukushima. Neutrons freed during nuclear fission collided with chloride ions in the saltwater, transforming chloride atoms into a radioactive form of sulfur, UCSD explains. When the seawater hit the hot reactors, almost all of it vaporized. To prevent explosions, operators vented the steam, which carried the radioactive sulfur into the atmosphere.

After observing the spike in radioactive sulfur in La Jolla on March 28, the UCSD scientists traced the air's path back to Fukushima based on patterns of atmospheric conditions from the National Oceanic and Atmospheric Administration.

The chemists were certain that this radiation came from Fukushima because although cosmic rays can also produce radioactive sulfur, it rarely ends up in the layer of air just above the ocean, which is where the spike in radiation was measured.

For more:
- read the release in the UCSD News Center
- read the article abstract from PNAS (sub. req. for full article)

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