The secular change of radioactivity's concentration in airdust from Fukushima Daiichi plant at Osaka, Nagoya and Ibaraki

The polluted air dust by radioactive waste from Fukushima No. 1 nuclear power plant have been measured from March 2011 onward at Osaka (Toyonaka), Aichi (Nagoya) and Ibaraki (Mito and Hitachi). Radioactivity of ¹³¹I, ¹³⁴Cs, ¹³⁶Cs and ¹³⁷Cs were measured by HPGe γ-ray spectrometer for the 365, 605, 819 and 662 keV γ-ray, respectively. Iodine-131 had been first detected from March 18 in Nagoya, and ¹³⁴Cs and ¹³⁷Cs began to be observed after 10 days. Concentrations of ¹³¹I, ¹³⁴Cs and ¹³⁷Cs in the air were in the range of 0 to 14, 0 to 18 and 0 to 20 mBq/m³, respectively, with two peaks in April 6 and 17. These peaks may be suggested by the existence of high concentration of polluted air mass which is rotated around the earth. (author)