Determination of boron in nuclear materials by isotope dilution technique. Part I

Summary The application of the mass-spectrometric stable-isotope dilution technique for the determination of microgram and submicrogram quantities of boron in nuclear materials is described. An adequate amount of spike solution (enriched in¹⁰B) is added to the sample and the mixture is treated chemically to ensure isotopic equilibration. Boron is then separated as methyl borate by distillation from phosphoric acid and converted into sodium tetraborate suitable for isotopic analysis by surface ionization in a mass spectrometer. The results for boron content in a standard boric acid solution, reagents, ammonium diuranate, uranium dioxide, sintered pellets of UO₂ and uranyl nitrate are given. Owing to the simplicity, accuracy and high precision a possible application of the method would be its use for routine boron determinations in a natural uranium processing plant and/or as a standard method for intercomparison with other analytical methods.

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Zusammenfassung Die Anwendung der massenspektrometrischen Isotopenverdünnungsmethode auf die Borbestimmung im Bereich von Mikrogramm und darunter in Reaktormaterialien wurde beschrieben.Eine entsprechende Menge von angereichertem¹⁰B wird einer Probe zugegeben und die Mischung zur Herstellung des Isotopengleichgewichtes chemisch behandelt. Das Bor wird dann als Methylborat durch Destillation aus der phosphorsäurehaltigen Lösung abgetrennt und zum Zweck einer massenspektrometrischen Isotopenanalyse in Natriumtetraborat umgesetzt.Der Borgehalt in H₃BO₃-Standardlösungen, Reagenzien, Ammoniumdiuranat (ADU), UO₂, gesinterten UO₂-Pastillen und Uranylnitrat wird angegeben. Wegen der Einfachheit, Genauigkeit und Empfindlichkeit könnte diese Methode sowohl für die routinemäßige Borbestimmung bei der Herstellung von Brennstoffelementen mit natürlichem Uran als auch für die Standardisierung analytischer Methoden angewandt werden.

     

Magnetic properties of Mn-oxide nanoparticles dispersed in an amorphous SiO2 matrix

Samples of Mn-oxide nanoparticles dispersed in an amorphous SiO₂ matrix with manganese concentration 0.7 and 3 at% have been synthesized by a sol-gel method. Transmission electron microscopy analysis has shown that the samples contain agglomerates of amorphous silica particles 10-20 nm in size. In silica matrix two types of Mn-rich particles are dispersed, smaller nanoparticles with dimensions between 3 and 10 nm, and larger crystalline areas consisting of aggregates of the smaller nanoparticles. High-temperature magnetic susceptibility study reveals that dominant magnetic phase at higher temperatures is λ-MnO₂. At temperatures below T_C=43 K strong ferrimagnetism originating from the minor Mn₃O₄ phase masks the relatively weak magnetism of λ-MnO₂ with antiferromagnetic interactions. Magnetic field dependence of the maximum in the zero-field-cooled magnetization for both the samples in the vicinity of 40 K, and a frequency shift of the real component of the ac magnetic susceptibility in the sample with 3 at% Mn suggest that the magnetic moments of the smaller Mn₃O₄ nanoparticles with dimensions below 10 nm are exposed to thermally activated blocking process just below the Curie temperature T_C. Appearance of a maximum in the zero-field-cooled magnetization for both the samples below 10 K indicates possible spin glass freezing of the magnetic moments at low temperatures which might occur in the geometrically frustrated Mn sublattice of the λ-MnO₂ crystal structure.     

Surface of Zn-Mn-O and its role in room temperature ferromagnetism: An XPS analysis

The existence of ferromagnetism in Zn-Mn-O semiconductor samples and dependence on the preparation condition were investigated. We systematically examined the samples with manganese concentration ranging from 0 to 10 at.%, prepared by a solid state reaction route using (ZnC₂O₄·2H₂O)_1−x and (MnC₂O₄·2H₂O)_x as precursors. Thermal treatment was carried out in air at temperatures ranging from 400 to 900 °C. The samples were investigated by X-ray diffraction, transmission electron microscopy, magnetization measurements and XPS spectroscopy. XPS surface composition, chemical analysis and depth profiling were successfully employed on powder revealing the chemical composition at the surface of the grains and underneath. The present investigation suggests that physical properties and observed room temperature ferromagnetism might be due to grain surface effects. It seems that the ferromagnetic phase is correlated with oxygen build up at the surface.     

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The novel heteronuclear complexes [{cis-PtCl (NH₃)(μ-pyrazine)ZnCl (terpy)}](ClO₄)₂ (Pt-L1-Zn) and [{cis-PtCl (NH₃)(μ-4,4′-bipyridyl)ZnCl (terpy)}](ClO₄)₂ (Pt-L2-Zn) (where terpy = 2,2′:6′,2′′-terpyridine, L1 = pyrazine, L2 = 4,4′-bipyridyl) were synthesized and characterized. The pK_a values were determined, and based on them it was established that the π-acceptor ability of the pyrazine bridging ligand is more affective on lower pK_a values. The kinetic measurements of the substitution reactions with biologically relevant ligands, such as guanosine-5′-monophosphate (5′-GMP), inosine-5′-monophosphate (5′-IMP) and glutathione (GSH), were studied at pH 7.4. The reactions were followed under pseudo-first-order conditions by UV–Vis spectrophotometry. The order of reactivity of the investigated biomolecules for the first reaction is 5′-GMP > 5′-IMP > GSH, while for the second is 5′-IMP > GSH. Pt-L1-Zn complex is more reactive than Pt-L2-Zn. The cytotoxic activity of heteronuclear Pt-L1-Zn and Pt-L2-Zn complexes was determined on human colorectal cancer cell line (HCT-116) and human breast cancer cell line (MDA-MB-231). Both complexes significantly reduced cell viability on tested cell lines and exerted significant cytotoxic effects, with better effect on HCT-116 cells than cisplatin, especially after 72 hr (IC₅₀ < 0.52 μM). The Pt-L2-Zn complex showed higher activity against human breast cancer cells (MDA-MB-231) than cisplatin after 72 hr. The higher reactivity toward DNA constituent and significant cytotoxic activity may be attributed to the different geometry, Lewis acidity of different metal centers, as well as, to choice of bridging ligands.     

Determination of the soil-to-grass transfer of 137Cs and its relation to several soil properties at various locations in Serbia

Transfer coefficients of (137)Cs from soil to grass were determined for the terrain around the city of Kragujevac in central Serbia. Mass activity concentrations of (137)Cs in soil and grass samples were determined with a high-purity Ge-detector (HPGe). The activity concentration at the depth of 20 cm was found to be in the range of 14.92-124.05 Bq kg(-1), whereas the activity in grass for the same location was in the range of 4.60-84.95 Bq kg(-1). Transfer factors (TFs) were in the range of 0.07 up to 1.94. Dependences of TFs on different soil characteristics were presented graphically. Weak dependences were determined between them. Absalom's model was used to predict TFs based on soil characteristics: pH value, contents of clay, exchangeable potassium and humus. A comparison of measured and predicted values from Absalom's model is shown graphically. It has been found that Absalom's model might be carefully used for the prediction of (137)Cs in grass for specific regions.     

Chronic exposure to zinc oxide nanoparticles increases ischemic-reperfusion injuries in isolated rat hearts

The use of zinc oxide nanoparticles (ZnO NPs) in numerous products is increasing, although possible negative implications of their long-term consumption are not known yet. Our aim was to evaluate the chronic, 6-week oral exposure to two different concentrations of ZnO NPs on isolated rat hearts exposed to ischemic-reperfusion injury and on small intestine morphology. Wistar rats of both sexes (n = 18) were randomly divided into three groups: (1) 4 mg/kg ZnO NPs, (2) 40 mg/kg ZnO NPs, and (3) control. After 6 weeks of treatment, the hearts were isolated, the left ventricular pressure (LVP), the coronary flow (CF), the duration of arrhythmias and the lactate dehydrogenase release rate (LDH) were measured. A histological investigation of the small intestine was performed. Chronic exposure to ZnO NPs acted cardiotoxic dose-dependently. ZnO NPs in dosage 40 mg/kg maximally decreased LVP (3.3-fold) and CF (2.5-fold) and increased the duration of ventricular tachycardia (all P < 0.01) compared to control, whereas ZnO NPs in dosage 4 mg/kg acted less cardiotoxic. Goblet cells in the small intestine epithelium of rats, treated with 40 mg ZnO NPs/kg, were enlarged, swollen and numerous, the intestinal epithelium width was increased. Unexpectedly, ZnO NPs in both dosages significantly decreased LDH. A 6-week oral exposure to ZnO NPs dose-dependently increased heart injuries and caused irritation of the intestinal mucosa. A prolonged exposure to ZnO NPs might cause functional damage to the heart even with exposures to the recommended daily doses, which should be tested in future studies.     

Determination of the soil-to-grass transfer of 137Cs and its relation to several soil properties at various locations in Serbia

Transfer coefficients of ¹³⁷Cs from soil to grass were determined for the terrain around the city of Kragujevac in central Serbia. Mass activity concentrations of ¹³⁷Cs in soil and grass samples were determined with a high-purity Ge-detector (HPGe). The activity concentration at the depth of 20 cm was found to be in the range of 14.92–124.05 Bq kg^?1, whereas the activity in grass for the same location was in the range of 4.60–84.95 Bq kg^?1. Transfer factors (TFs) were in the range of 0.07 up to 1.94.

Dependences of TFs on different soil characteristics were presented graphically. Weak dependences were determined between them. Absalom's model was used to predict TFs based on soil characteristics: pH value, contents of clay, exchangeable potassium and humus.

A comparison of measured and predicted values from Absalom's model is shown graphically. It has been found that Absalom's model might be carefully used for the prediction of ¹³⁷Cs in grass for specific regions.     

Room temperature ferromagnetism in Zn-Mn-O

Zn-Mn-O semiconductor crystallites with nominal manganese concentration x=0.01, 0.04 and 0.10 were synthesized by a solid state reaction method using oxalate precursors. A sintering procedure was carried out in air at 500 and 900  ^°C. The samples were investigated by X-ray diffraction, magnetization measurements and electron paramagnetic resonance. X-ray diffraction spectra reveal that the dominant crystal phase in the Zn-Mn-O system corresponds to the wurtzite structure of ZnO. Room temperature ferromagnetism is observed in Zn-Mn-O samples with manganese concentrations x=0.01 and 0.04 sintered at low temperature (500  ^°C). Saturation magnetization in the x=0.01 sample is found to be at . The ferromagnetic phase seems to be developed by Zn diffusion into Mn-oxide grains.     

The mechanism of hydrogen randomization in the stilbene molecular ion

Hydrogen randomization of the stilbene molecular ion preceding the formation of the [M—methyl]-ion is discussed.