Measurement of the Ambient Radioactivity and Estimation of Human Radiation Exposure Dose in Tokyo with Regard to the Radioactive Substance Leakage Due to the Fukushima Daiichi Nuclear Power Plant Accident

Abstract

The massive earthquake that occurred in northeastern Japan on March 11, 2011 triggered a severe nuclear accident at Fukushima Daiich Nuclear Power Station. Since the accident, concentrations of radionuclides in airborne dust, foodstuffs and drinking water, and &gannma;-ray dose rate have been monitored at Fukazawa, Setagaya-ku in Tokyo. Based on the results obtained until May 31, we tried to calculate internally exposed dose due to ¹³²Te, ¹³¹I, ¹³²I, ¹³⁴Cs and ¹³⁷Cs, and externally exposed dose calculated from air dose rates. Cumulative dose in one year from the day when we started monitoring was estimated to be 425.1μSv, which does not exceed 1mSv, the annual dose limit of public given by ICRP.