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  • Author or Editor: S. Nagao x
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Abstract  

Geochemical association of137Cs and239,240Pu in the surface sediments from two oligotrophic and mesotrophic lakes in Japan was studied by sequential chemical extractions. The fractions separated were exchangeable and bound to carbonate, bound to oxides, bound to organic mattersulfides, and residual. The137Cs and239,240Pu were mainly associated with the organic matter-sulfides and residual fractions but exhibited the different vertical profiles at both lakes. The differences in association patterns between the lakes may be controlled by transport of these nuclides by organic settling particles to the bottom sediments and decomposition of the organics in the sediments.

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Abstract  

To evaluate the radionuclide migration from the atmosphere to the ground surface, atmospheric deposition samples were collected from 1993 to 2001 with a basin set up at Tokai-mura, Japan. Monthly samples were evaporated to dryness to obtain residual samples and measured with a Ge detector for 7Be, 40K, 137Cs and 210Pb. According to the analysis, clear seasonal variations with spring peaks of deposition weight and deposition amounts of all the radionuclides were found. The analysis also showed that these radinuclides can be divided into two groups, each having different carrier particle sizes and, hence, different deposition processes.

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Abstract  

The association properties of Pu with aquatic humic substances in a 0.01M NaClO4 solution at pH 6–8 were studied on the basis of molecular size distribution. Seven humic substances were isolated from river water and groundwaters using XAD extraction technique. They were used for comparing their effects on the association of Pu. In the presence of humic acid, the dominant molecular size of Pu was 100–30 kDa. In the presence of fulvic acid, Pu exhibited three dominant molecular sizes: 30–10 kDa, 30–5 kDa, and less than 5 kDa. The association of Pu-humus complexes might be controlled by the molecular size distribution of humic substances and characteristics of their respective size fractions.

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Abstract  

On dehydration of La[Co(CN)6]5H2O, the color of the complex, changes from white to pale blue at around 230C. Heating the pale blue specimen, the color changes to deep blue at around 290C. This deep blue specimen is easily rehydrated to a pink one. As reported previously, in the pale blue specimen, Co3+ ions are situated in the center of the D4h crystal field formed by six CN- ions. The deep blue specimen is due to the presence of [Co(CN)4]2- ions in which Co2+ was situated in a Td coordination field formed by four CN- ions and the Co-C bond length is 1.67 Ĺ. The pink species corresponded to trans-[Co(CN)4(H2O)2]2- and the bond lengths of Co-C and Co-O are 1.89 and 1.85 Ĺ, respectively. The Raman spectra of the complex observed at 25C displays two bands at 2157 and 2176 cm-1 associated with the vibration of C-N bond, and the band of 2157 cm-1 was split into two bands, 2150 and 2156 cm-1, at around 100C. When the complex was heated to around 230C, three new bands were observed at 2103, 2116 and 2141 cm-1. The bands of 2103 and 2116 cm-1 were assigned to the stretching vibration of C=N bonding to Co2+. The band of 2141 cm-1 was assigned to the stretching vibration of the inverted CN- as follows: Co-C=N-La→Co-N=C-La. The activation energy for the inversion of CN- was estimated as 67 kJ mol-1.

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Abstract  

The association properties of Am with aquatic humic substances in a 0.01M NaClO4 solution at pH 6-8 were studied on the basis of molecular size distribution. Ten humic substances isolated from river water with different water quality (pH 3.9-8.0 and dissolved organic carbon (DOC) concentration of 2-40 mg/l) were used for comparing their effects on the association of Am. The molecular size distribution of Am in the presence of humic substances from an uncolored river water (DOC 2 mg/l) was different from that at the experimental systems using humic substances from brownish and high DOC (14-40 mg/l) river waters.

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Abstract  

The concentration of pore water uranium in six sediments from oligotrophic, mesotrophic, acidotrophic and dystrophic lakes was measured by inductively coupled plasma-mass spectrometry. Profiles of pore water U can be divided into two groups such as low (17±7 ng/l) and high concentration (69±30 ng/l). These values were 1–2 orders of magnitude higher than that of lake waters (6±4 ng/l) due to the release of U from the sediments by decomposition of organic materials. Variations in pore water U concentrations seem to relate to the differences in pore water pH, the association forms, and their contents of U in the lake sediments.

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