Abstract
Increase of I-131 concentration in wheat top was caused by the direct dry deposition of the I-131 in the air, not by the direct wet deposition of the rainfall, especially above 10 mm/day, by 7-35% compared with the preceding day. 2) In contrast to the wheat top, the increase of I-131 concentration in surface soil (0-0.5 cm) was caused by the direct wet deposition of I-131 in the rainfall, not by direct dry deposition of I-131 in the air. The increase rate of I-131 caused by rainfall was 9-90% compared with the preceding day. 3) It was estimated that the decrease of approximately 50% during the period from 9:00 on May 8 through 9:00 on May was caused by the volatilization of I-131 from the surface soil under the clear wheather and the high air temperature. 4) Fifty-seven % of I-131 deposited on the soil has been retained in 0-1.0 cm horizon; the remainder distributed in 1.0-7.5 cm horizon at June 20. On the other hand, about 100% of Cs-137 and Cs-134 has been retained in 0-1.0 cm horizon at June 20. 5) About 10% of I-131 was removed from wheat top by gentle washing with water. It was estimated that the same level percent of I-131 would be removed from wheat top by the rainfall. 6) It was confirmed chemically that 94.1% of I-131 in the rain water was in the form of iodate, 4.4% was iodide. This ratio was almost the same as the stable iodine in the rain water.
