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 (99)Mo/(99m)Tc, (132)Te/(132)I, (129 m)Te/(129)Te, (131)I, (137)Cs, (136)Cs, (134)Cs, (140)Ba/(140)La, (110 m)Ag, and (95)Nb were observed and, with the exception of (137)Cs and (134)Cs, these radionuclides decreased to below the limit of detection in the middle of June. The activity ratio of atmospheric (134)Cs/(137)Cs in aerosols decreased over time almost following physical decays. Therefore, the (134)Cs/(137)Cs 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 (137)Cs and (134)Cs would be necessary for the sedimentology of lake sediment.