"Detecting Fukishima" from North America was no mean feat .. it was akin to hearing the footfall of an ant several miles away. The radiometric procedure here w

"Detecting Fukishima" from North America was no mean feat .. it was akin to hearing the footfall of an ant several miles away. The radiometric procedure here was (IIRC) replace a large number of air filter mats in a large number of HVAC units and after a week to cycle them back and then reduce the "contaminated" mats down to samples that sat within highly sensitive high crystal volume spectrometers for 72 hours or more. The 'normal' environmental radiation event count level in 40 litres of doped Sodium Iodide scintillation Crystals (if that's what was used) at some 80m above ground level is between one and two thousand events per second. The Fukishima signature gamma events came to a few thousand in 72 hours (again, IIRC) whch had to be teased out from a flood of other events many magnitudes greater in count. Absolutely not enough to be concerned about, but a seriously interesting bit of detection work.