Matrix effects on epithermal neutron activation analysis of various kinds of reference materials

The improvement obtained by epithermal neutron activation analysis was studied in terms of the detection sensitivity and precision in the γ-ray spectrometry for geological and biological reference samples. For geological samples, small improvement was observed only for the elements As, Ba, Sb, Se and U. For biological samples, however, large improvement was observed for As, Br, Sb and U. The ratio of the resonance integral to the effective thermal-neutron capture cross section was observed for 19 nuclides. The effect of the (n, p) reaction to the determination of Al and Mg by the ordinary reaktor-neutron activation analysis was estimated.     

Radiation-induced reaction of ethylene–cyclohexane–carbon tetrachloride system

The γ-ray-induced reaction of ethylene with carbon tetrachloride in cyclohexane was carried under a pressure of 30 kg/cm² and at a temperature of 20°C. The liquid and the solid products were obtained. Their structures were discussed on the basis of infrared absorption spectra and differential thermal analysis curves. The liquid product is considered to be ethylene–carbon tetrachloride telomer. The solid product consists of three components, differing slightly in molecular structure and molecular weight. To clarify the reaction process, some runs with the ethylene–cyclohexane–(ethylene–carbon tetrachloride telomer) system were also carried out. In this system, only solid product was obtained. Thus, it is concluded that the reaction proceeds stepwise, the first step being the telomerization reaction and the second the graft polymerization of ethylene onto the telomer produced in the first step.     

Spintronic Transport through Polyphenoxyl Radical Molecules

The coherent quantum transport properties through the spin-polarized polyphenoxyl radical molecule have been investigated, using the density-functional-derived tight-binding model and the Green's functions method. The majority and minority spin components exhibit considerably different transmission spectra in the vicinity of the Fermi level. Namely, each spin component carries a different amount of current when the bias voltage is applied between the two electrodes that sandwich the polyradical molecule. Therefore, if the magnetization axis of the polyradical is fixed by the external magnetic field, and if the spin flip does not occur during the transmission, the assumed molecular bridge is expected to work as a spin filter or a spin valve. Furthermore, as long as the bias voltage is weak, the total spin current is observed to be larger than the current through its reduced molecular form. It indicates that the adsorption of some chemical species on the radical sites can be sensed by the change in conductance of the molecular bridge.     

Molecular exclusion chromatography in studies of the vanadium- and nickel-containing species in residual oil

A residual oil sample prepared from a crude oil is chromatographed on a column having a molecular-weight exclusion limit at about 5000. Three-dimensional chromatograms (absorbance/wavelength/time) are recorded with a u.v.-visible rapid-scanning detector. The elution profiles of vanadium- or nickel-containing species are obtained by applying atomic absorption spectrophotometry to fractions of the column effluents. Both vanadium- and nickel-containing species are detected over the whole molecular-weight range available with the column. The elution profiles of vanadium and nickel differ; the major elution peak for vanadium appears at a slightly lower molecular-weight region of the chromatogram than that for nickel. By reference to the real-time recorded absorption spectra of the effluents, it is suggested that at least some of the metals are present as metalloporphyrins.     

Transfer factors of 31 elements in several agricultural plants collected from 150 farm fields in Aomori, Japan

Soil-to-plant transfer factors of 31 stable elements were determined by neutron activation analysis. The transfer factor is one of the important parameters used to estimate the internal radiation dose from radionuclides through food ingestion. In the present study, 12 species of agricultural plants such as root crops, fruit vegetables, green vegetables and pasture grasses, and their soils were collected from 150 farm fields in Aomori prefecture, Japan. The elements described are those that could be detected by this method, which include both essential and nonessential elements for plant growth. The concentrations of individual elements in the cultivated soil samples for each plant were similar in values and their standard deviations were within one order of magnitude, because of the relatively narrow geographic sampling area. The elements were classified into two groups, each having different transfer factor characteristics. In the first group of elements there was an inverse correlation between the transfer factors and the concentrations of elements in the soil, especially for Cl, K and Ca. In the second group, especially Sc and Co, however, the transfer factors were independent of the concentrations of elements in the soil.     

Aggregation behavior of latex particles in shear flow confined between two parallel plates

In this study, the aggregation and breakup behaviors of latex particles in shear flow confined between two parallel plates were investigated using an in situ observation apparatus with a laser scanning confocal microscope. To investigate the effects of shear rate and the gap width between two parallel plates on the size and structure of the aggregates in the steady state, the distributions of the projected cross-sectional area and perimeter-based fractal dimension of the aggregates were measured. As a result, the average size of the aggregates decreases as shear rate increases and the gap width decreases due to the hydrodynamic effect acting on the aggregates. The size distributions of the aggregates become narrow as the gap width decreases. In addition, the fractal dimension, that is, the structure of the aggregates, was almost independent of shear rate and the gap width and approximately 1.2, which suggests that the aggregates are relatively compact.     

Photocatalytic degradation of hexachlorocyclohexane (HCH) by TiO2-pillared fluorine mica

A significant effect of clay host was observed on the photocatalytic activity of TiO2; TiO2-pillared fluorine mica exhibited two orders of magnitude higher activity than TiO2 and TiO2-pillared montmorillonite for the photocatalytic degradation of gamma-HCH.     

Production and characterization of actinide metallofullerenes

We have, previously, reported on the HPLC elution behavior of the Th, Pa, U, Np, and Am metallofullerenes and the UV/vis/NIR absorption spectra of the Th@C₈₄ and U@C₈₂ species. In this paper, the followings are reported: (1) Pu metallofullerenes were produced and their HPLC elution behavior was investigated using a radiotracer technique. The HPLC chromatogram of this metallofullerene was found to be almost the same as that of the Np and Am metallofullerenes. (2) The oxidation states of Th@C₈₄ and U@C₈₂ produced in macroscopic quantities were examined by XANES (X-ray absorption near edge structure) measurements. The oxidation state of the U atom in the C₈₂ fullerene cage was estimated to be 3+ with the formal charge of the ionic molecule being U³⁺@C₈₂ ^3-.     

Ion-pair extractions by the use of planar and non-planar extracting solvents

The effect of extracting solvent was studied on the ion-pair extraction reactions with a special interest in the effect of molecular shape (planar or non-planar) of the solvent. The following two reactions were investigated: (HNN)_o + (Q⁺)_W (Q·NN)_o + (H⁺)_W (Extraction I); (Q-ClO₄)_o + (Pi^–)_w (Q·Pi)_o + (ClO ₄ ^– )_w (Extraction II), where HNN, NN^–, Pi^–, and Q⁺ represent 1-nitro-2-naphthol, its base form (1-nitro-2-naphtholate), picrate, and a cationic species, respectively. Above extraction equilibria were confirmed to hold in cases of various extracting solvents including planar solvents (1-chloronaphthalene, etc.) and non-planar solvents (1,2-dichloroethane, chloroform). An approximately linear relationship was found to exist between the extraction constants of Extraction I (logK _ex ^I ) and the Kosower's Z-value of extracting solvents. It was also found that the compatibility between the molecular shape of the ion-pair complexes and that of the extracting solvents affected the extractability to a considerable extent.