Oxygen isotope exchange in oxygen-bearing compounds of uranium

Isotope exchange is reported for gaseous oxygen in contact with the following uranium compounds: -Na₂UO₄, -Na₂UO₄, Na₂U₂O₇, UO₃(A), -UO₃, -UO_2.94 and U₃O₈.; qualitative tests have also been done with UO₂F₂ and Cs₂UO₂Cl₄. The times of half-exchange have been determined as functions of temperature for U₃O₈, -UO_2.94, Na₂U₂O₇ and -Na₂UO₄; diffusion coefficients for oxygen have been calculated for UO₃(A), -UO₃, Na₂U₂O₇, -Na₂UO₄ and -Na₂UO₄. Activation energies have been deduced for diffusion and surface exchange. All the oxygen atoms in these compounds are equivalent as regards isotope exchange; the above activation energies increase with the UO ratio in some cases. Diffusion-limited exchange tends to show periodic oscillations in rate not ascribable to errors of measurement; a mechanism is proposed for this.     

铀和铀同位素的离子交换过程研究

在浓缩铀同位索的阳离子交换法中,UC_2~(2+)在离子交换树脂中的传质问题具有特别重要的意义.但迄今未见有详细的报道.本文对阳离子交换树脂—HCl溶液体系中的UO_2~(2+)—H~+正、逆交换,特别对~(235)UO_2~(2+)—~(238)UO_2~(2+)交换动力学及机制作了研究和探讨.     

Mathematical model of boron isotope separation by chemical exchange reaction

Journal of Radioanalytical and Nuclear Chemistry - In this paper, the dependence of the number of theoretical plates on temperature and reflux ratio was theoretically studied by a mathematical...     

Modeling study of two-step photodissociation method of isotope enrichment

A general comprehensive model of the two-step photodissociation method of isotope enrichment for diatomic reactants was constructed. The model includes kinetic and absorption processes, isotopic species, and temperature. Criteria to measure different aspects of enrichment were established. The results show that, in general, isotopic mixing by kinetic processes can be controlled. The relative importance of intensities of excitation sources for the two steps depends on the degree of saturation of the first-step absorption transition. For the specific system modeled, i.e., the dissociation of HBr followed by scavenging with NO, the model predicts that detection of bromine enrichment is possible. The important processes and their influence on enrichment were identified, and optimization of experimental parameters was modeled.     

Substoichiometric isotope dilution analysis for uranium by synergic extraction

Substoichiometric extraction of uranyl ion in a synergic system of a chelating reagent and a neutral ligand is described. The system is based on a substoichiometric amount of 2-thenoyltrifluoroacetone (TTA) and an excess of tributylphosphate (TBP); this is compared with a system involving a substoichiometric amount of trioctylphosphine oxide and an excess of TTA. The reproducibility of the substoichiometric extraction is 0.46 or 0.62%, respectively. The former method is superior because extraction of uranyl ion with TBP alone is negligible. The method is applicable to > ca. 10 μg of uranium.     

Lithium isotope separation by chemical exchange with polymer-bound azacrown compounds

The chromatographic separation of lithium isotopes was investigated by chemical exchange with the recently synthesized polymer-bound dibenzo pyridino diamide azacrown (DBPDA) and reduced dibenzo pyridino diamide azacrown (RDBPDA). Column chromatography was employed for the determination of the effect of solvents and ligand conformation on the separation coefficients. The maximum separation coefficients, , for the DBPDA and RDBPDA at 20.0±0.02°C with acetonitrile as eluent, were found to be 0.034±0.002 and 0.035±0.002, respectively. The isotope separation coefficient and adsorption capability of the lithium ion on the DBPDA and RDBPDA were only slightly dependent on ligand structure, but strongly dependent on the solvent. DBPDA and RDBPDA appeared to have almost the same value for the isotope separation coefficient of lithium.     

Mass-spectrometric determination of uranium by means of isotope dilution analysis

The paper describes experience concerning the determination of uranium in nuclear fuels by mass-spectrometric isotope dilution analysis. As a spike, the solution of²³³U was used. The method was applied to the uranium content determination in non-irradiated and irradiated samples of nuclear fuels.     

Determination of uranium element concentration and235U isotope abundance by neutron activation analysis

A new neutron activation technique has been developed for the determination of uranium element concentration and²³⁵U isotope abundance in nuclear safeguards and reference material samples based on the activation of bare and cadmium-covered samples with different thermal to epithermal neutron flux ratios and on the combination of the two corre-sponding delayed-fission neutron measurements. The principle of the new technique can be applied also to improve multi-element neutron activation analysis.     

Radioiodination of amitriptyline by isotope exchange

The catalysed isotope exchange method was studied with the aim to elaborate the optimal procedure for labeling of amitriptyline with iodine¹²⁵I. Besides the catalysts published, cuprous salts and ammonium sulphate, a series of transition metal complexes as catalysts were tested at different reaction conditions. The best result (91% radiochemical yield) was achieved with trans-chlorocarbonylbis-(triphenylphosphine) iridium complex (Vaska catalyst) and sonification.     

Determination of rare earth impurities in high purity uranium by isotope dilution analysis

Summary An isotope dilution method for the determination of rare earth impurities in uranium has been developed and Ce, Nd, Sm, Eu and Gd have been determined in uranium oxide samples. The method involves isotopic dilution with enriched isotopes of the rare earths being measured, followed by the separation of rare earths from uranium. A mass spectrometer with thermionic source was used to determine the relative isotopic abundances in each of these rare earths. All these five elements were analysed selectively by preferential evaporation technique. Trace concentrations down to parts per billion range can be measured with good sensitivity and accuracy.

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Bestimmung von Verunreinigungen an Seltenen Erden in hochreinem Uran durch Isotopenverdünnungsanalyse

Zusammenfassung Eine Isotopenverdünnungsmethode wurde ausgearbeitet zur Bestimmung von Ce, Nd, Sm, Eu und Gd in Uranoxidproben. Das Verfahren umfaßt isotopische Verdünnung mit angereicherten Isotopen der zu bestimmenden Elemente und nachfolgende Abtrennung der Seltenen Erden von Uran. Die relativen Isotopenhäufigkeiten wurden mit Hilfe eines Massenspektrometers mit thermischer Ionenquelle bestimmt. Alle fünf Elemente wurden durch selektive Verdampfung analysiert. Spurenkonzentrationen bis herab zum ppb-Bereich konnten mit guter Empfindlichkeit und Genauigkeit erfaßt werden.

     

Homogeneous isotope exchange between tungsten(VI) and Keggin and Dawson type uranium polyoxotungstophosphates

The present paper is concerned with the isotope exchange between¹⁸⁵W and tungsten, and³²P and phosphorus respectively, in uranium(IV) trivacant Keggin and Dawson polyoxotungstophosphate complexes, in water. These studies were carried out at different concentrations and temperature. The isotope exchange rate increases with the temperature and the reagents' concentration. The experimental results show that the complexes are labile kinetically.     

尿样中铀同位素的ICP-MS快速测量技术研究

核事故状态下的应急处理,要求对环境介质中的放射性核素进行快速分析。尿样中铀同位素测量作为内照射剂量评价的主要手段,其分析效率越高,则对核事故中涉铀人员的安全救治越及时、有效。而尿样中其它无机离子是铀含量的106倍,导致ICP-MS测量过程中尿盐堵塞进样毛细管。为降低样品的含盐量并获得较好的检测结果,本文对样品预处理过程进行优化。采用先加热氧化去除有机物,再进行1～10倍稀释后测试样品的铀同位素丰度及浓度。结果表明：将25 mL样品稀释至100 mL后效果最佳,分析方法不确定度为5.4 %,回收率95 %~105 %。     

Photo-oxidation of water by molecular oxygen: isotope exchange and isotope effects

Photolysis of (17,18)O-labeled water in the presence of molecular oxygen is accompanied by transfer of (17)O and (18)O isotopes from water to oxygen, demonstrating that photoinduced oxidation of water does occur. The reaction exhibits the following isotope effect: oxidation of H(2)(17)O is faster by 2.6% (in the Earth's magnetic field) and by 6.0% (in the field 0.5 T) than that of H(2)(18)O. The effect is supposed to arise in the two spin-selective, isotope-sorting reactions-recombination and disproportionation-in the pairs of encountering HO(2) radicals. The former is spin allowed from the singlet state; the latter occurs only in the triplet one. Nuclear spin sorting produced by these reactions proceeds in opposite directions with the dominating contribution of recombination, which provides observable (17)O/(18)O isotope fractionation in favor of magnetic isotope (17)O. Neither isotope exchange nor the reaction itself occurs in the dark.     

Isotopic analysis of single uranium and plutonium particles by chemical treatment and mass spectrometry

The isotopic composition of single uranium and plutonium particles was measured with an inductively coupled plasma mass spectrometer (ICP-MS) and a thermal ionization mass spectrometer (TIMS). Particles deposited on a carbon planchet were first analyzed with an energy dispersive X-ray spectrometer (EDX) attached to a scanning electron microscope (SEM) and then transferred on to a silicon wafer using a manipulator. The particle on the silicon wafer was dissolved with nitric acid and the isotopic ratios of U and Pu were measured with ICP-MS and TIMS. The results obtained by both methods for particles of certified reference materials showed good agreement with the certified values within the expected uncertainty. The measurement uncertainties obtained in this study were similar for both mass spectrometric methods. This study was performed to establish the method of particle analysis with SEM, EDX, the particle manipulation and chemical preparation technique, and the measurement of isotopic ratios of U and Pu in a single particle by mass spectrometry.     

Deuterium labeling of glyprolines by isotope exchange

Deuterium-labeled 5-oxo-Pro-Arg-Pro, 5-oxo-Pro-His-Pro-Gly-Pro-NH₂, and Phe-Pro-LeuPro-Ala were synthesized. The effect of the method of peptide deposition on the catalyst, the catalyst nature, temperature, and structure of peptides on the inclusion of deuterium with the formation of the appropriate number of isotopomers was demonstrated. The 5-oxo-Pro-Arg-Pro, 5-oxo-Pro-His-Pro-Gly-Pro-NH₂, and Phe-Pro-Leu-Pro-Ala peptides containing, on average, 4.6, 7.7, and 5.4 deuterium atoms per peptide molecule, respectively, were obtained.     

Carbon monoxide isotope enrichment and separation by pressure swing adsorption

Simulations of three different 3-bed 3-step pressure swing adsorption (PSA) cycles were carried out to study the enrichment and recovery of ¹⁴CO from an isotopic mixture of ¹⁴CO, ¹³CO and ¹²CO using NaX zeolite. Each PSA cycle included feed pressurization/feed (FP/P), heavy reflux (HR) and countercurrent depressurization (CnD) steps; they differed only in the way the CnD step was carried out: PSA Cycle I was carried out under total reflux (i.e., with no ¹⁴CO heavy product production); PSA Cycle II was carried out with discontinuous ¹⁴CO heavy product production; and PSA Cycle III was carried out with continuous ¹⁴CO heavy product production. The effects of the CnD step valve coefficient (c _v ), heavy reflux ratio (R _R ), and cycle time (t _cyc ) on the PSA process performance were determined in terms of the ¹⁴CO enrichment, ¹⁴CO recovery and CO feed throughput. The results showed that there was essentially no limit to the extent of the ¹⁴CO enrichment, despite the inherently low ¹⁴CO/¹²CO (1.05) and ¹⁴CO/¹³CO (1.12) separation factors for these isotopes on NaX zeolite. Under total reflux an optimum c _v was found for the CnD step and ¹⁴CO enrichments as high as 152 were obtained. Using the optimum c _v under finite reflux, a ¹⁴CO enrichment approaching 20 and a ¹⁴CO recovery approaching 100 % were easily achieved with discontinuous (PSA Cycle II) or continuous (PSA Cycle III) ¹⁴CO heavy product production. There was essentially no difference in the performance of PSA Cycles II and III, a counterintuitive result. The ¹⁴CO enrichment and the ¹⁴CO recovery both increased with decreasing CO feed throughputs and higher R _R , which were always very close to unity.     

Dry-column chromatography of uranium. Application to chemical analysis of monazite and phosphate rock for uranium

Summary A dry-column Chromatographic technique has been applied to the separation of uranium from complicated matrices. It has been demonstrated that operating parameters of thin-layer chromatography on silanized silica gel in isopropyl ether-tetrahydrofuran-nitric acid (65203) can be transferred to this technique. Chromatograms are thus easily developed on dry packed column with the solvent system of the type used in the TLC. Uranium is eluted off the column and determined with Arsenazo III spectrophotometrically. The technique is successfully applied to the determination of uranium in monazite and phosphate rock samples with good precision and accuracy.

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Trockensäulenchromatographie des Urans. Anwendung zur chemischen Analyse von Monazit und Phosphorit

Zusammenfassung Zur Abtrennung des Urans aus komplizierten Matrices wurde die Trockensäulenchromatographie verwendet. Wie gezeigt werden konnte, lassen sich die Bedingungen der Dünnschichtchromatographie (DSC) auf silanisiertem Silikagel mit Isopropylether-Tetrahydrofuran-Salpetersäure (65203) auf das genannte Verfahren übertragen. Chromatogramme sind daher auf trocken geschichteten Säulen mit Lösungsmittelsystemen der DSC herstellbar. Uran wird eluiert und mit Arsenazo III spektrophotometrisch bestimmt. Das Verfahren wurde zur Uranbestimmung in Monazit und Phosphorit erfolgreich angewendet.