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  • Author or Editor: T. Mitsugashira x
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Summary  

In the wide pH range of 4 to 10, distribution ratios of Am(III)-humate species to free Am(III) ions (D AmHA = [Am(III)HA]/[Am(III)]free) were determined at 10 ppm (4.7 . 10-5 eq/dm3) of humic acid and 0.1M NaClO4 by a cation-exchange equilibrium method under N2 atmosphere. The D AmHA was insensitive to an increase in pH (logD AmHA ≈ 2.6-2.8), which indicates the formation of mixed hydroxo-humate complexes. The present D AmHA value is larger than the estimated value from available stability constants for ternary complexations by spectroscopic analysis (1.4-2.1) and is markedly smaller than that of Eu(III) obtained by the dialysis method (3.7-8.0) reported in the literatures. The D AmHA obtained in the present study is widely applicable to estimate the actinide(III) and lanthanide(III) sorption on minerals in the presence of humic and fulvic acids.

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Abstract  

Complexation of Am(III) with humic acid was studied at various pHs in 0.1M NaClO4. The stability constants of the Am(III)—humate complexes were determined by a cation-exchange method. The values of log 1 and log 2 increased slightly with increases of pH from 4 to 6 and were found to be 6.9 and 11.6, respectively, at a pH of 5. Markedly larger values than these were obtained by a solvent extraction method. This discrepancy was also revealed by summarizing data from several literature sources. It is very likely that this can be ascribed to decreases in either humic acid and/or the extractant from the extraction system due to humate interactions at the aqueous-organic interface.

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Abstract  

The separation of trivalent actinides and lanthanides was studied by using newly developed tertiary pyridine-type anion-exchange resin embedded in silica beads. Chromatographic elution experiments were carried out by using a packed column of the new resin and methanol-hydrochloric acid solution as an effluent. We confirmed that the actinides were eluted well from the elution bands of lanthanides. Actinides and lanthanides were eluted according to the reverse order of their atomic number.

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Summary  

In order to develop the partitioning-transmutation system for the reduction of high-level radioactive wastes, the group and mutual separation of actinides and rare earth elements in spent fuels is required. In the present work, a chromatographic separation of trivalent actinides (Am and Cm) and rare earth elements was examined in hydrochloric acid/methanol mixed solvents by using a pyridine resin embedded in high-porous silica beads. In a 70 vol% hydrochloric acid (11.7 mol HCl/dm3)/30 vol% methanol mixed solvent, the elution curves of the trivalent actinides were separated completely from those of rare earth elements at room temperature. The present paper discusses the separation behavior of trivalent actinides and rare earth elements as a function of flow rate, temperature and solvent compositions.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: T. Mitsugashira, M. Hara, T. Ohtsuki, H. Yuki, K. Takamiya, Y. Kasamatsu, A. Shinohara, H. Kikunaga, and T. Nakanishi

Abstract  

The alpha-decay of a low energy isomer of 229Th at about 3.5 eV was sought by producing it through the (g,n) reaction on a 230Th target. Thorium isotopes in the reaction products were isolated and purified by anion exchange chromatography in a concentrated nitric acid medium to remove lanthanides fission products. The thorium fraction was further purified by samarium fluoride coprecipitation and the precipitate was mounted as a source for a-spectroscopy. Decaying a-signals were observed in the energy region that was expected for 229mTh, i.e., between 4.83 and 5.08 MeV. The half-life of the decaying component was determined from repeated experiments to be 13.9±3 hours.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Yagi, Y. Shiokawa, S. Suzuki, M. Hara, I. Satoh, K. Masumoto, and T. Mitsugashira

Abstract  

Neutron emission from the d-d nuclear fusion reaction, D/d,n/3He, in and on titanium metals /titanium sponge and the mixture of titanium powder/ trapped deuterium at about 1 atm has been ascertained by using a high resolution liquid scintillation detector. The neutron emissions from 11 samples which were provided under wide varieties of conditions were measured by temperature change in the range of liquid nitrogen temperature to 350 °C. As a result, it was proved that the neutron emission observed can be divided into two types, such as cooling and heating, by the evolved conditions. Moreover, by estimating the neutron emission efficiencies of samples, it was suggested that the neutron emission reactions are closely related to the deuterium trapped in the surface of titanium metal.

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Abstract  

Highly sensitive neutron activation analysis of uranium and thorium in high quality silica and aluminium has been investigated using the Japan Materials Testing Reactor (JMTR), having a thermal neutron flux higher than 1014 n/cm2/s. In order to determine ultra-low contents of uranium and thorium,239Np and233Pa as activation products were separated by using anion exchange and LaF3 coprecipitation methods. As a result, a number of interfering radioactive isotopes containing double neutron capture product such as183Ta were removed completely from the isolated239Np and233Pa fraction and the detection limits for uranium and thorium were found to be 2·10–12 g and 4·10–13 g, respectively.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Yagi, T. Mitsugashira, I. Satoh, M. Hara, Y. Shiokawa, K. Inoue, K. Masumoto, and S. Suzuki

Abstract  

As a new fact, the neutron emission from the d-d nuclear fusion reaction in a SiO2–D2 system has been confirmed as well as that in the Ti–D2 system. By using a liquid scintillation detector, the neutron emissions from 8 sample materials consisted of SiO2, in which a small amount of deuterium was adsorbed chemically on the surface layer, were measured in the range of temperature between liquid nitrogen temperature and 400 °C. As a result, it was demonstrated that the neutron-emission reactions take place predominantly on the surface layer of sample material.

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Abstract  

Coprecipitation methods with SmF3 and BaSO4 were developed in order to evaluate the radioequilibrium of natural decay nuclides series in high purity silica and lead. The present study revealed that228Th,230Th, and231Pa in silica and210Po, probably210Pb, in lead were enriched in much higher concentrations than their precursor nuclides.

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Abstract  

The separation of Am and Cm by using the tertiary pyridine resin embedded in silica beads was studied in nitric acid/methanol mixed solvent system. This separation system of Am and Cm is very simple and easy. The adsorption and separation behaviors of Am and Cm were investigated with changing the nitric acid and the methanol concentrations. It was confirmed that Am can be almost completely separated from Cm.

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