Monitoring of aerosols in Tsukuba after Fukushima Nuclear Power Plant incident in 2011

Artificial radionuclides were released into the atmosphere by the Fukushima Dai-ichi Nuclear Power Plant incident after a strong earthquake on 11 March 2011. Aerosol monitoring at the Geological Survey of Japan, Tsukuba, was started 20 d after the incident. Radionuclides such as 99Mo/99mTc, 132Te/132I, 129mTe/129Te, 131I, 137Cs, 136Cs, 134Cs, 140Ba/140La, 110mAg, and 95Nb were observed and, with the exception of 137Cs and 134Cs, these radionuclides decreased to below the limit of detection in the middle of June. The activity ratio of atmospheric 134Cs/137Cs in aerosols decreased over time almost following physical decays. Therefore, the 134Cs/137Cs activity ratio in the averaged air mass in this study could be regarded as homogeneous although those of several reactors in the Nuclear Power Plant were not ascertained. A further research on the released 137Cs and 134Cs would be necessary for the sedimentology of lake sediment.

► Aerosol monitoring in Tsukuba was started 20 d after the incident.
► Most radionuclides decreased to below the limit of detection in the middle of June.
► The 134Cs/137Cs activity ratio decreased with time exponentially.
► The average aerosols seemed homogeneous with regard to the Cs isotope.