My analysis of beta counts in California was from some simple EPA data. Here is a more detailed analysis of samples from Seattle: Fission Products in Seattle Reveal Clues about Japan Nuclear Disaster

By measuring the energy of the gamma rays from the filters, these guys have identified exactly which fission products have made their way across the Pacific. And this in turn allows them to make a number of interesting inferences about what has gone wrong at Fukushima.

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[T]here are a huge number of possible breakdown products from nuclear fission in a reactor and yet the Seattle team found evidence of only three fission product elements–iodine, cesium and tellurium. “This points to a specifific process of release into the atmosphere,” they say.

Cesium Iodide is highly soluble in water. So these guys speculate that what they’re seeing is the result of contaminated steam being released into the atmosphere. “Chernobyl debris, conversely, showed a much broader spectrum of elements, reflecting the direct dispersal of active fuel elements,” they say.

However, this comes from an analysis of just the first five days after the fission products were detected (data collected on Mar 17-18), so it does not reflect more recent events.