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  • Author or Editor: M. Koyama x
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Abstract  

A simple method has been developed for evaluating the neutron spectrum and the temperature by using U, Sb, Cr, Co and Lu as monitors and successfully applied to the routine analysis. For most of nuclides, amounts determined by the method showed reasonable agreements with those added. However, there have been found several nuclides which gave erroneous results beyond the permissible limits. In the case of128I, the reason for the deviation was found to lie on the normalization factor of -ray abundances that are in common use. This was confirmed by using I2 doped polyacethylene which is a material highly resistant to ionizing radiations.46Sc,175Yb and several other rare earth nuclides are discussed as well.

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Abstract  

In order to improve the accuracy of reactor neutron activation analysis, flux gradients and spectrum changes in the irradiation capsule have been studied at the Kyoto University Reactor (KUR). The flux and spectrum monitoring samples of Fe, Co, Au, Sb, U and Ni were placed at several positions in a polyethylene irradiation capsule of 24 mm inner diameter and 98 mm length, and were irradiated in a pneumatic irradiation facility (Pn-2). The flux gradients were found to be rather negligible in the vertical (axial) direction while they were considerable in the radial one. The flux gradient was around 5%/cm for thermal neutrons and 10%/cm for epithermal and fast neutrons. The spectrum changes were dependent on the materials (polyethylene and silica) filled in the capsule. Based on these observations, the effect of the flux gradients and spectrum changes on the accuracy of reactor neutron activation analysis was discussed.

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Abstract  

More than 2000 samales of land plant leaves, mostly of tree, have been analyzed by neutron activation analysis in order to find out macroscopic relations between distributions of chemical elements in plants and soil characteristics. The distributions of the elements in plants were also examined from the view point of botanical taxonomy or phylogeny. New species which accumulate Co, rare earths, Ba, Ra, heavy halogens and some other elements have been found. Capability or potentiality for accumulating elements could be related to higher ranks of taxonomy, that is, genus or family. The nature of soil is also found to have profound effects on the extent of accumulation of elements in plants.

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Abstract  

A rapid separation of radioactive cesium by the solvent extraction method was investigated. Cesium ions are quantitatively extracted with [Cr(NH2C6H5)2(NCS)4] into nitrobenzene. EDTA is an effective masking agent for other polyvalent cations. The extracted cesium can be back-extracted into the aqueous phase by shaking with 6N HCl. The method was applied to samples of a natural mixture of fission products and a reactor coolant. The decontamination factors for other predominant isotopes in fission products were 102∼104. The separation of137mBa from a mixture of137Cs and137mBa is also described.

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Abstract  

A new type of silica-based chelating extraction resin, DtBuCH18C6/SiO2-P, was prepared by impregnating a crown ether derivative, 4,4,(5)-di(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6), into the porous silica/polymer composite particles (SiO2-P). The adsorption of Sr(II) and some other fission product elements was investigated by a batch adsorption experiment in HNO3 medium. It was found that Sr(II) exhibits a strong adsorption onto the extraction resin, while the other fission product elements show almost no or only weak adsorption. The adsorption kinetics of Sr(II) was explained by assuming as the rate-controlling step the complex-formation reaction between Sr(II) and DtBuCH18C6 contained in the extraction resin. The rate equation of Sr(II) adsorption was determined as:-d[Sr(II)]/dt = k[Sr(II)][DtBuCH18C6][NO3 ]0.5.

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Abstract  

Content of 40 elements in plant leaves, soils and rocks collected from several sampling sites in Okayama Prefecture was analyzed by instrumental neutron activation analysis using the Research Reactor of Kyoto University. Of these, 16 elements were taken up, and the relationship among their amounts in plants, rocks and soils was discussed, focusing mainly on the essential elements of higher plants and related elements in the periodic table. Although most element contents in plant were different among species, the mediam values of the most non-essential elements in the leaf were lower than the contents in the soil and rock samples. However, essential elements showed significantly higher median values than those in the soil and rock samples. Most element contents in leaves showed a logarithmic normal distribution. The normal distribution was observed in most essential elements except for zinc, while non-essential elements did not show a normal distribution. The results obtained by analysis of variance, showed that the plant species studied could be divided into four major groups, namelyDicotyledoneae, Monocotyledoneae, Gymnospermae andPteridophyta. In general,Dycotyledoneae andPteridophyta had higher element contents thanMonocotyledonaeae andGymnospermae.

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Journal of Thermal Analysis and Calorimetry
Authors: Y. Sato, A. Funakoshi, K. Okada, M. Akiyoshi, T. Matsunaga, S. Koyama, M. Ozawa, and T. Suzuki

Abstract  

The fundamental properties of tertiary pyridine resin (TPR) and its mixtures with methanol/HCl and HNO3 were investigated in order to evaluate the thermal stability of TPR and to determine the conditions necessary to avoid runaway reactions. Based on experimental DSC results, it was found that TPR with HCl was thermally stable, but strong decomposition was possible with TPR in the presence of HNO3. From the results of heating tests on the gram scale, TPR with HNO3 reacted violently under high temperature regardless of HNO3 concentration and presence or absence of methanol. However, it was considered that the violent exothermic reaction could be controlled by heating temperature.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Koyama, J. Takada, K. Kamiyama, N. Fujii, J. Inoue, K. Issiki, and E. Nakayama

Abstract  

In order minimize the possible contamination during storing and pre-treatment of such pure samples as ice and snow collected in Antarctica, trace elements in experimental tools such as bottles, beakers, tubings and filters were determined by neutron activation analysis. By using well certified tools, ice and snow samples from Antarctica and high mountains in China and in Japan were analyzed. Relative concentrations of volatile elements such as Zn, Cd, As, Sb or Ag to Al or Fe which are major components in the earth crust were found to be 10 to 1000 times higher than in the ordinary soil for the samples from Antarctica and Mt. Naimonanyi in China.

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Abstract  

A multi-functional separation process is proposed as one of the technologies for implementing the Adv.-ORIENT (Advanced Optimization by Recycling Instructive ElemeNTs) Cycle concept [<cite>1</cite>]. The tertiary pyridine-type anion exchange resin (TPR) embedded in silica beads (silica-supported TPR) was demonstrated suitable for the separation process of actinides from spent fuel. In this process, hydrochloric acid (HCl) and a mixture of nitric acid (HNO3) and methanol (MeOH) are used as eluents. In order to apply this process to an engineering plant scale, two important issues must be evaluated to prove the system suitability. One is an environmental aspect represented by the use of HCl solution which is corrosive to many materials. The other is clarification of the reactive safety of silica-supported TPR and the HNO3–MeOH solvent mixture. Four types of metals, Ta, Zr, Nb, and Hastelloy-B (28%Mo–Ni) were selected as candidate materials which are anti-corrosive toward HCl. Corrosion experiments were conducted in HCl type simulated high level liquid waste (SHLLW) solution at room temperature for a maximum 720 h and at 90 °C for 336 h. Ta showed an all-round anti-corrosion property in HCl type SHLLW solution, and Hastelloy-B was only acceptable at room temperature. Thermal analysis by differential scanning calorimetry was done to investigate the thermal stability of silica-supported TPR-NO3/MeOH/HNO3 mixtures. Heating experiment results on a gram scale were also obtained and evaluated to determine the conditions necessary to avoid runaway reactions. As a result, it was confirmed that a vigorous exothermic reaction can be avoided by controlled decrease of temperature.

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Abstract  

A method is described for the determination of trace metal ions, V, Al, Cu, Mo Zn, and U, in natural water samples by neutron activation analysis, using organic coprecipitation as a preconcentration method. The preconcentration of trace elements was accomplished by converting the dissolved trace metal ions into the oxine chelates atpH 5.2 and extraction of the chelates witho-phenylphenol which is a liquid above 56 °C and solidifies at room temperature. After cooling the extraction system, the fine particles of the organic phase were collected on a millipore filter and the precipitate was air-dried in a clean environment. The solid extract was wrapped up in a sheet of clean polyethylene and subjected to neutron irradiation in a reactor for less than 10 min at a thermal flux of 2·1013 n·cm−2·sec−1. γ-Ray spectrometry by a coaxial Ge(Li) detector connected to a 1024-channel PHA was performed on the irradiated sample without further chemical separation, and thus the ppb level concentration of the elements in natural water samples could be determined. The fundamental study of the collection of the trace elements is also described.

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