Arrival time and magnitude of airborne fission products from the Fukushima, Japan, reactor incident as measured in Seattle, WA, USA

We report results of air monitoring started due to the recent natural catastrophe on 11 March 2011 in Japan and the severe ensuing damage to the Fukushima Dai-ichi nuclear reactor complex. On 17–18 March 2011, we registered the first arrival of the airborne fission products 131I, 132I, 132Te, 134Cs, and 137Cs in Seattle, WA, USA, by identifying their characteristic gamma rays using a germanium detector. We measured the evolution of the activities over a period of 23 days at the end of which the activities had mostly fallen below our detection limit. The highest detected activity from radionuclides attached to particulate matter amounted to 4.4 ± 1.3 mBq m−3 of 131I on 19–20 March.

► We measured the arrival of airborne fission products from the Fukushima reactor incident in Seattle, USA.
► We estimate a transport time of 5–6 days – faster than previously thought.
► From the composition of radionuclides several conclusions are drawn on the state of the reactor at the time of release.
► These data will provide a strong cornerstone in a global analysis of the transport of radionuclides from the reactor incident.