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  • Author or Editor: Y. Yamada x
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Abstract  

The surface seawater and marine organisms were collected on the Japanese coast and analyzed for their137Cs concentrations during the 1980's. The137Cs concentrations in surface seawater decreased almost exponentially with time and the137Cs removal rate constant was estimated to be 0.0445 y−1. The137Cs concentrations in marine organisms also decreased almost exponentially with time. The environmental half-lives of137Cs in muscle and viscera of fish, crustacea, and seaweed were estimated from the measured decreases of137Cs concentrations.

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Abstract  

Marine sediment cores were taken from Sagami Bay of the western Northwest Pacific and analyzed for 239+240Pu and 137Cs activities. A significant correlation was observed between 239+240Pu and 137Cs activities in sediment cores, i.e., their vertical profiles. The measured activities which were used to obtain the inventories of 239+240Pu and 137Cs in the sediment column, showed large variations, ranging from 36 to 474 MBq/km2 for 239+240Pu and 49 to 652 MBq/km2 for 137Cs. 239+240Pu inventories in the sediment from one region in the Bay, Sagami Nada were 5–10 times greater than those predicted from atmospheric global fallout 42 MBq/km2 at the same latitude. On the other hand, 137Cs inventories, with a mean value of 297±168 MBq/km2, were much less than predicted, 2040 MBq/km2. The activity ratios of 239+240Pu/137Cs obtained, with a mean of 0.65±0.17, were significantly greater than the ratio predicted from fallout, 0.021. Furthermore, there was a clear relationship between both 239+240Pu and 137Cs inventories and the water content, indicating that higher inventories may be attributed principally to concentration in, and scavenging by, fine-grained particles.

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Abstract  

Molecular orbital calculations have been performed to obtain the electron density and electric field gradient at the iron nucleus of tetracarbonylethene iron Fe(CO)4(C2H4) produced by UV-irradiation of pentacarbonyliron cocondensed homogeneously with ethene in a low temperature matrix, so as to estimate the Mössbauer parameters of the species. Mössbauer isomer shifts and electron densities at iron nuclei (O) of Fe(CO)n (n=5,4,3,2) as well as Fe(CO)4(C2H4) are discussed: they have fairly good linear relationship to give –0.27 mm/s/aO –3. An isomer of Fe(CO)4(C2H4) produced via thermal reactions of Fe(CO)4 with ethene in a stratified matrix is discussed by comparing the calculated and observed Mössbauer parameters.

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Abstract  

The UV photolysis of pentacarbonyliron isolated in low temperature nitrogen matrix by continuous or pulsed deposition was studied by means of Mössbauer technique. Unstable species such as Fe/CO/n /n=2–4/ were produced by UV irradiation and their Mössbauer parameters were measured. The yields of unstable species were found to be influenced by the deposition method of nitrogen matrix.

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Abstract  

Molecular orbital calculations were performed to obtain electron density and electric field gradient at the iron nucleus of iron carbonyls Fe(CO)n (n=2–5) so as to estimate the Mössbauer parameters, of these species. The calculated values were compared with the experimental values obtained in low temperature nitrogen matrices; structures of these species were optimized to fit the observed values.

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Abstract  

The UV-induced photochemical reactions of pentacarbonyliron with ethene in a low temperature nitrogen matrix were studied by means of the Mössbauer technique. Fe/CO/4/C2H4/ was produced by UV-irradiation of penfacarbonyliron in close proximity to ethene molecules in a pure ethene matrix, or a homogeneous cocondensed matrix. The other products were obtained via thermal reactions with ethene of Fe/CO/4 trapped in stratified matrices.

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Abstract  

Four sediment cores were collected from Tokyo Bay and analyzed for their 239+240Pu and 137Cs concentrations. Shallow nearshore sediments from Tokyo Bay have 239+240Pu inventories which average 214±14 MBq/km2. They are five times greater than the supply expected from the atmospheric global fallout at the same latitude of 42 MBq/km2. The measured mean 137Cs inventory of 433±93 MBq/km2 is approximately one fifth the value expected from global fallout. Furthermore, the 239+240Pu/137Cs activity ratios, with a mean ratio of 0.50±0.14, are significantly greater than the ratio expected from the global fallout of 0.021. Excess 239+240Pu inventories can be considered to have been introduced into Tokyo Bay as weathering products by soil erosion, transported via rivers and winds, and to be much more efficiently scavenged from seawater by particles resuspended at the sediment-water interface.

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Abstract  

Mössbauer parameters of tin compounds, Sn(CH3)2H4–n (n=0, 1, 2, 3, 4), isolated in low temperature matrices were related to electronic properties at the tin nuclei obtained by molecular orbital calculations. Structures of novel species, Sn(CH3)2 and Sn(CH3)H, produced via photodissociation of matrix-isolated Sn(CH3)3H and Sn(CH3)2H2, respectively, were determined on the basis of molecular orbital calculations as compared with Mössbauer parameters. The correlations between Mössbauer quadrupole splitting and calculated electric field gradient using STO-3G or MINI-4 were found to depend on the valence of tin atoms because of poor allowance for basis sets in describing highly polar molecules.

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Summary Ni1-xZnxFe2O4 (0≤x≤1) mixed ferrite nanoparticles encapsulated with amorphous-SiO2 were prepared by a wet chemical method. Particle sizes were controlled to range from 2.6 to 33.7 nm by heat treatment, and the particle size dependence of saturation magnetization Ms was investigated for the x=0.5 region. The Ms value decreased abruptly for particle sizes below about 6 nm. From the temperature dependence of the magnetization under field-cooled and zero-field-cooled conditions, blocking temperatures Tb were observed to be between 28 and 245 K depending on the particle size. At the blocking temperature, the superparamagnetic spins in the particle are supposed to be blocked against the thermal fluctuation energy. A smaller particle volume causes a lower blocking temperature; so an extremely small particle would be strongly affected by thermal fluctuation.

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Abstract  

Unstable novel species produced by photolysis of ferrocene (Cp2Fe) isolated in low-temperature matrix were studied by means of the57Fe Mössbauer spectroscopy. On the UV-irradiation of57Fe-enriched ferrocene co-condensed with CCl4 in low-temperature N2 matrix (20 K), unknown high spin ferrous species (I.S.=0.90±0.01 mm/s, Q.S=1.94±0.02 mm/s) were produced as well as ferricinium ion [Cp2Fe]+ (I.S.=0.52±0.01 mm/s, Q.S.=0.0 mm/s). On the annealing, these photoproducts disappeared to reform ferrocene by the reverse reaction in the matrix. The mechanisms of the photochemical reaction were discussed.

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