RADIOISOTOPES

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In order to reveal whether the H atom (s) directly bonded to α-carbon in each aliphatic ether can participate in T-for-H exchange reaction, the T-for-H exchange reaction between the ether having normal chain structure and the T-labeled compound was observed at 20°C under the equilibrium conditions. The reaction was carried out in the liquid-solid system. Each ether used includes an atom having lone pairs, and the ethers are diethyl ether, 2, 2'-dichlorodiethyl ether, and 1, 2-dichloroethyl ethyl ether. In the exchange reaction, poly (vinyl alcohol) having T-labeled OH groups (i.e., OT group) was used as a solid sample material, and each ether dissolved in p-xylene was used as a liquid sample material. For comparison, Biphenyl ether was also used in this work (50-80°C) . The concentration of the solution was set at 0.5 mol⋅dm^-3, respectively. Based on the results obtained in this work, the following four have been clarified. (1) The reaction mass of diethyl ether is the same as that of 2, 2'-dichloro diethyl ether, and the mass of 1, 2-dichloroethyl ethyl ether is about 3/4 times that of the former two materials. (2) The H atoms bonded to α-carbon in each ether can participate in the T-for-H exchange reaction when they contact with T-labeled compound. (3) Comparing the rate constant for diphenyl ether with that for other materials previously obtained (by using the A″-McKay plot method), Biphenyl ether has a similar ability to aniline and benzaldehyde for causing this exchange reaction. In other words, H atoms bonded to α-carbon in certain ethers have a similar reactivity to those of both -NH₂ in aniline and -CHO in benzaldehyde. (4) H atoms bonded to α-carbon in ethers seem to cause not only T-for-H exchange reaction, but also other chemical reaction (s) .

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This paper discusses the influences of global-scale radioactive fallout on polished rice in Japan. For this purpose, a set of paddy topsoil and unpolished rice samples was collected annually from experimental paddy fields at seventeen stations across Japan during the years from 1959 to 1995.
According to the graph presenting year-to-year variations in the nationwide averages of ⁹⁰Sr and ¹³⁷Cs contents (mBq/kg) of the polished rice samples, the year 1963 marked the first and highest peaks with 269 for ⁹⁰Sr and 4179 for ¹³⁷Cs. The average fallout levels of the two nuclides were the highest in that year, too. Thereafter, ⁹⁰Sr and ¹³⁷Cs contents of the samples continued to decline drastically, the second peaks being in 1975 with 29·192 and the third peaks in 1995 with 5·46, respectively.
It can be conceived that ⁹⁰Sr and ¹³⁷Cs nuclides are directly taken into rice grains from stems, leaves and husks which are exposed to the atmosphere, or they are indirectly taken into the grains after they are absorbed from paddy topsoil by the roots. Through the analysis of contamination pathways, it was finally confirmed that for both ⁹⁰Sr and ¹³⁷Cs, the direct contamination comprised 70-95% in 1963 when the fallout levels were the highest, and that in the years following 1985 when the fallout nuclides ceased to be detected, the rice contamination was produced mainly through the indirect pathway.
Discussions also include the regional differences in the contents of polished rice, especially those between the Japan Sea coast and Pacific coast areas, differences in distribution rate of ⁹⁰Sr and ¹³⁷Cs between polished and unpolished rice, and relative difficulties of ⁹⁰Sr and ¹³⁷Cs being translocated in thoughout plants.

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