We have observed artificial radionuclides originated from the TEPCO Fukushima Daiichi Nuclear Power Plant accident. This paper presents our monitoring results(March to May, 2011) for (1) γ-ray dose rate (2) airborne radioactivity (3) radioactivity deposited onto the basin and (4) radioactivity in tap water. Regarding γ-ray dose rate, no increase was observed. A small amount of artificial radioactivity(
131I,
134Cs,
136Cs,
137Cs and
132Te) was found from airborne dust samples. While
131I was detected two weeks after the accident,
134Cs and
137Cs were detected three weeks after. Integrated amount of activity was 14mBq/m
3 for
131I, 11mBq/m
3 for
134Cs and 9.5mBq/m
3 for
137Cs. The monitoring results indicated that a plume with relatively high radioactivity passed through our monitoring station during April 6 - 7. Atmospheric diffusion simulation analyses reveal this.
131I,
134Cs and
137Cs were also measured from monthly-monitored deposition. Total depositions for three months were 4.2Bq/m
2 for
131I, 0.85Bq/m
2 for
134Cs and 0.84Bq/m
2 for
137Cs. No artificial radionuclide was found for tap water samples. The dose from these artificial radionuclides was estimated to be 0.23μSv/y, which was too small to cause health effects.
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