Too short a half-life to be from Japan.
What emits I-131>
I don’t believe I-131 has too short a half life to make it to Europe. Shortly after Fukushima went boom, air monitors in the US registered I-131. After the US detected it, France reported that they were receiving it. After about a month, France said that, given the rise in I-131 over the preceding weeks, they were instituting precautions for young children and pregnant women advising them to avoid dairy for the time being. I recall a dairy in VT dumping milk that had exceeded FDA limits on I-131 but the US is not making much effort to measure anything coming from Fukushima. I don’t know if or when France lifted that advisory. True that I-131 has an 8 day half life but at the 8 day mark, half of it is still present so this could be from Fukushima.
Fukushima is producing short half lived gases like Xenon and, at times, TEPCO reports I-131. There is a debate as to how the melted molten fuel cores, which now rest somewhere in the basement of the reactors, are undergoing fission to produce these gases and other contaminants. Some people believe that one of the fuel cores (#2) reached the water table and cooled off enough to restore criticality (begin to undergo fission as if it were a functioning power plant) and some, including TEPCO, are claiming that the short half life products are being produced by spontaneous fission. Since no one wants to believe we have ‘live’ reactors ‘running’ outside their containment vessels -there is incentive to believe that it is instead ‘spontaneous fission.’ The fact that TEPCO is not currently reporting I-131 may be a feature of where and what they are choosing to measure and report. Here’s an article on the ‘criticality’ versus ‘spontaneous fission’ issue which notes that Xenon was detected in Fukushima November 2nd.
http://ex-skf.blogspot.com/2011/11/tepco-to-redefine-its-idea-of.html
Nuclear fuels like Uranium-239 undergoing fission split apart and one of the products is I-131