When emergency technicians in Fukushima attempted to cool the overheating reactor with seawater, they didn't realize they'd be enabling a set of incredibly accurate calculations that would allow researchers half a world away to calculate how bad the leak had been, and where it was going in the environment.
When the seawater hit the reactor, the leaking neutrons pinged off a proton from the chlorine in the liquid, transforming it into 35S, a radioactive isotope of sulfur. Vaporizing from the heat, it was then vented, and formed sulfur dioxide and sulfate particles, and was blown across the ocean to San Diego, where it was detected by UCSD's Scripps Institution of Oceanography.
The researchers there were able to use some pretty hefty mathematics to figure out just how much energy was leaking. "You know how much seawater they used, how far neutrons will penetrate into the seawater and the size of the chloride ion. From that you can calculate how many neutrons must have reacted with chlorine to make radioactive sulfur," said researcher Antra Priyadarshi.
While the radiation levels in California were far too low to be of any concern to humans, back in Fukushima they were 365 times higher than normal — 400 billion neutrons were released per square meter surface of the cooling pools.
Since these radioactive isotopes can be used as markers, the researchers also hope they can use them to trace the labeled sulfur through the ecology of Japan, to understand how the radiation will spread and effect the environment.