When I was working on my BS in Physics we measured Cesium-137 from nuclear accidents and weapons testing. We wanted to see if we could detect any change due to the release of material in Fukushima. We didn't see any change though because we were using a pretty insensitive gamma spectroscopy method and the increase was so small. I think they later found a small increase using a mass spectrometer.

It's amazing that you can still detect the results of the Chernobyl disaster on the opposite side of the world, decades later. That was one heck of a meltdown!