One-year time variations of anthropogenic radionuclides in aerosols in Tokyo after the Fukushima Dai-ichi Nuclear Power Plant reactor failures

We report on the results of monitoring of environmental radiation for one year (13 March 2011 to 12 March 2012), including air dose rates and the concentrations of radionuclides in aerosols in Tokyo, after the reactor failures at the Fukushima Dai-ichi Nuclear Power Plant. The air dose rates began to increase at 4:00-5:00 JST on 15 March 2011, and the maximum rate was observed at 10:00-11:00 JST. Two peaks were observed before 23 March 2011, and then the air dose rates decreased until March 2012. The time variations of concentrations of radionuclides in aerosols showed tendencies similar to those of air dose rates. Short-lived radionuclides (Mo-99 (Tc-99m), Te-129m (Te-129), Te-131m, Te-132 (I-132), I-133 and Cs-136) were under the detection limit during April 2011. Iodine-131 was detected until early June 2011, and long-lived radionuclides (Cs-134 and Cs-137) were detected intermittently for one year. Based on our results, gamma doses and committed effective doses resulting from inhalation were estimated.