Abstract
Analysing the air-masses covering Japan, we can find the origin and the movement of radioactive fallout transported. The fallout originated in the Bikini and in the Arctics are transported with the Ogasawara air-mass and the Siberia air-mass respectively, but the one in the Southwest Siberia is transported from the north with the Siberia air-mass or rapidly from the west with the strong westerlies. The fallout discharged in the troposphere spreads over in a considerably large area in the atmosphere after about 3 months travel from its original site.
