Plutonium, 137Cs and uranium isotopes in Mongolian surface soils.

Plutonium (238Pu and 239,240Pu), 137Cs and plutonium activity ratios (238Pu/239,240Pu) as did uranium isotope ratio (235U/238U) were measured in surface soil samples collected in southeast Mongolia. The 239,240Pu and 137Cs concentrations in Mongolian surface soils (<53 µm of particle size) ranged from 0.42 ± 0.03 to 3.53 ± 0.09 mBq g-1 and from 11.6 ± 0.7 to 102 ± 1 mBq g-1, respectively. The 238Pu/239,240Pu activity ratios in the surface soils (0.013-0.06) coincided with that of global fallout. The 235U/238U atom ratios in the surface soil show the natural one. There was a good correlation between the 239,240Pu and 137Cs concentrations in the surface soils. We introduce the migration depth to have better understanding of migration behaviors of anthropogenic radionuclides in surface soil. We found a difference of the migration behavior between 239,240Pu and 137Cs from 137Cs/239,240Pu - 137Cs plots for the Mongolian and Tsukuba surface soils; plutonium in surface soil is migrated easier than 137Cs.

210Pb deposition in the far East Asia: controlling factors of its spatial and temporal variations.

In order to better understand the behavior of (210)Pb deposition in Far East Asia, comprehensive data of monthly (210)Pb deposition, which includes several time-series and spatial distribution data at 14 stations in Japan and 2 stations in Taiwan, were analyzed. Pb-210 deposition at most of the sites exhibited a typical seasonal change with higher values in winter and lower values in summer; especially, the greatest (210)Pb deposition in the world occurred in winter at sites beside the Japan Sea. The deposition behavior of (210)Pb in Far East Asia differed between winter and summer. The meteorological phenomenon peculiar to winter of the Japan Sea side, i.e., formation of the Japan Sea convergence zone, might cause the high (210)Pb concentration in rainwater, as may heavy snowfall. The (210)Pb concentration in rainwater showed long-term variability, although this differed between winter and summer. This long-term variability may be related to climatological factors such as El Niño.