Neutron powder diffraction studies of di­methyl sulfoxide

The crystal structure of per­deutero­di­methyl sulfoxide, (CD₃)₂SO, has been refined at 2 and 100 K, and characterized as a function of temperature up to 275 K against high‐resolution neutron powder diffraction data. The structure determined previously by Thomas, Shoemaker & Eriks [Acta Cryst. (1966), 21 , 12–20] (T = 278 K) is shown to remain down to 2 K. At 2 K, the S—O bond distance is 1.495 (2) Å. The fact that the mol­ecule is distorted from ideal C_s point symmetry may be explained by the short D⋯O contacts of the respective methyl groups.     

分光光度法测定三氧化铀中的硫酸根

采用TBP-萃淋树脂吸附三氧化铀样品中的铀,硫酸根与铬酸钡进行交换反应后,直接比色法测定硫酸根的含量。实验中研究了三氧化铀样品中硫酸根含量测定的样品制备、分离、反应酸度,煮沸时间,铬酸钡用量等影响因素。优化条件下,采用硝酸(5mol/L)淋洗、1mL HCl溶液(2.5mol/L)调节溶液中酸浓度、使用2mL BaCrO_4进行交换反应、煮沸3min,得到方法相对标准偏差小于10%,加标回收率为92.9%～110%。实验结果表明,直接显色的测定方法灵敏、快速、准确度高。方法测定条件易于获得,适于推广应用。     

Neutron activation analysis of uranium via239Np

A method is described for the analysis of uranium by neutron activation. The sample is brought into solution and the neptunium present is reduced to oxidation state (IV); quantitative extraction of²³⁹Np in the acidified aqueous phase (0.4<pH<1) is performed with a solution of HTTA (0.2M) in benzene. The use of a low-power reactor (100 kW_thermal) enables determination of uranium at a lower concentration limit of 33 ng for periods of irradiation. cooling and measurement of 3 hours, 24 hours and 900 seconds, respectively.     

The structures of fluorides X. Neutron powder diffraction profile studies of UF6 at 193°K and 293°K

Neutron diffraction studies on polycrystalline UF₆ have been carried out at 193°K and 293°K. At both temperatures, UF₆ is orthorhombic with the space group Pnma (D¹⁶_2h) and Z = 4. Measured lattice parameters are a = 9.924 (10) Å, b = 8.954 (9) Å, c = 5.198 (5)Å at 293°K and a = 9.843 (11), b = 8.920 (10), c = 5.173 (6) Å at 193°K. The neutron diffraction patterns were analyzed by the least-squares profile-fitting technique. The final values of $\text{R =}\text{∑}\text{i}\text{(|I}{}_{\mathrm{<mtext>o</mtext><mtext>i</mtext>}}\text{? I}{}_{\mathrm{<mtext>o</mtext><mtext>i</mtext>}}\text{|)/∑ I}{}_{\mathrm{<mtext>o</mtext><mtext>i</mtext>}}$ over the pattern points, where I_oi is a background corrected measured intensity, were 0.081 at 193°K and 0.133 at 293°K.On cooling, the hexagonal close-packing tends to become more regular, and the FF distances external to a UF₆ octahedron contract. The octahedra are nearly regular with a mean UF distance of 1.98 Å, a mean FF edge of 2.80 Å, and a FUF angle of 90.0° at 193°K.     

Neutron powder diffraction study of perdeuterodimethyl sulfone

The crystal structure of perdeuterodimethyl sulfone, (CD₃)₂SO₂ or C₂D₆O₂S, has been refined at 4.5 K against high‐resolution neutron powder diffraction data. The structure determined previously by Sands [Z. Kristallogr. (1963), 119 , 245–251] at ambient temperature is shown to remain down to liquid helium temperature, and at 4.5 K the S—C and S—O bond distances are 1.441 (2) and 1.760 (2) Å, respectively. The molecules are distorted tetrahedra with C_2v point symmetry (crystallographic symmetry m2m for S and m for C, O and one D atom) and are linked through a network of weak hydrogen bonds in the C‐centred orthorhombic structure.     

Neutron diffraction study of the electrochemical passivation of nickel powder

With the aid of the Yamaoka mechanism and a.c. polarographic observables, rate constants for the homogeneous reduction of Co(III)pentammine complexes by Eu(II) are measured. Where comparison is possible, rate parameters obtained by this electrochemical procedure are found to be in good agreement with previous measurements by stopped-flow and pulse radiolysis procedures, with one exception. The order of reactivity for the halopentammineCo(III) complexes is found to follow the sequence RF²⁺>RCl²⁺>RBr²⁺>RI²⁺, where R=Co(III)(NH₃)₅³⁺. This and a pH dependence noted for the RF²⁺ case are suggestive of a predominantly inner sphere reaction pathway.     

Dissolution of uranium dioxide powder in carbonate-peroxide solution

Journal of Radioanalytical and Nuclear Chemistry - The effects of different dissolution parameters (solid–liquid ratio, peroxide concentration, carbonate concentration, countercation and pH)...     

Neutron activation analysis of rare earth impurities in metallic uranium

A method with a sensitivity of 2·10⁻⁷ to 1·10⁻¹⁰% has been developed for determining Yb, Ho, Dy, Gd, Eu, Sm and La impurities in metallic uranium by means of neutron activation. The method is based on a preliminary chromatographic separation of the total amount of rare earth elements from uranium by passing the solution in sulphuric acid through KU-2 cation exchange resin and eluting the traces of uranium retained by the resin with a solution of ascorbic acid. The rare earth impurities are then eluted from the resin with 4–5N HCl, evaporated, and irradiated for 20 hours with a neutron flux of 1.2·10¹³ n·cm⁻²·sec⁻¹. Subsequently the traces of the rare earth elements are co-precipitated with Fe(OH)₃, dissolved in concentrated HCl and separated from the iron and other impurities by passing the solution through Dowex 1X8 anion exchange resin in the chloride form. The individual rare earth elements are then separated from each other using KU-2 cation exchange resin and a solution of ammonium α-hydroxyisobutyrate as the eluant.     

Reaction of uranium monocarbide powder in oxidizing atmospheres

Thermogravimetric records have been obtained of uranium monocarbide oxidized in oxygen and in carbon dioxide under similar conditions. It is shown that the reactions are very similar. Initially, free carbon is formed during oxidation as well as UO₃ in O₂ or UO₂ in CO₂. In a second reaction step non-stoichiometric carbonates are formed, depending on experimental conditions. The carbonates decompose to stoichiometric oxides in the next step.Well crystallized α-UO₃ can be obtained by oxidation of uranium monocarbide in oxygen. The solid products containing UO₂ which slowly formed in carbon dioxide, are unstable in air.Infrared and X-ray analysis have been used to-compare related, solid structures. Activation energies have been determined of non-isothermal reactions, recorded below 750°C.     

Neutron powder‐profile study of chlorofluoromethane

The crystal structure of chloro­fluoro­methane, CH₂ClF, has been determined at 100 and 30 K using indexing, packing considerations and Rietveld refinement of neutron powder profiles. There is only one phase, in monoclinic space group P2₁ and with two mol­ecules in the unit cell occupying general positions. The structure has close packing in several directions and there are weak hydrogen bonds forming zigzag chains.     

Neutron activation analysis of pure uranium: Preconcentration of impurity elements

We have developed a radiochemical neutron activation analysis technique (RNAA) of pure uranium with using extraction chromatographic separation of ²³⁹Np from impurity elements in TBP-6M HNO₃ media. The estimation of influence of fission products of ²³⁵U on the results by radiochemical neutron activation analysis has been carried out. For it we have performed NAA with preconcentration of impurity elements. Experiments show that in this case the apparent concentration of Y, Zr, Mo, Cs, La, Ce, Pr, Nd exceeds the true concentration by 2500–3000 times. Therefore, determination of these elements is not possible by RNAA. This technique allowed to use the determination of 26 impurity elements with detection limit 10⁻⁵–10⁻⁹% by mass. This developed technique may be used for the determination of impurities in uranium and its compounds.     

Interferences in uranium oxidation states during dissolution of solid phases

The effects of iron on uranium oxidation states during sample dissolution were studied. A mineral acid mixture in anaerobic conditions was used for the dissolution the sample and the uranium oxidation states were determined by ion exchange. The first experiments were performed with pure iron chloride compounds. In the second stage, study was made of common iron-containing minerals. Uranium oxidation states were affected when the content of iron compound was as low as 10^-5M. In the case of the natural minerals, pyrite caused uranium to change to an increasingly reduced state, whereas goethite caused it to change to an increasingly oxidized state as the amount of mineral was increased. The interferences of the silicates fell between those of pyrite and goethite. The results indicate that a wide range of common bulk rocks with less than 20 wt% of iron-containing minerals can be reliable chemically analyzed for uranium oxidation state.     

Neutron activation determination of the uranium content of the primary coolant of water-water nuclear reactors

A neutron activation method for determination of uranium dissolved in the coolant of the first cycle of nuclear power stations is proposed. The method is based on preliminary concentration on activated carbon, irradiation with epithermal neutrons and gamma-spectrometry of²³⁹Np. The detection limit amounts to 1,3·10^–8 U/l. The method was sucessfully applied for the determination of uranium in the coolant of a nuclear power station.     

ESR studies of radical breakdown for di-t-butyl trioxide

ESR data show thermal breakdown of the title trioxide into peroxy and alkoxy radicals ROO^. and RO^., respectively. Equilibrium constants were calculated for the formation of tetroxide ROOOOR from two peroxy radicals. Their thermodynamic parameters were determined at temperatures ranging within 193–173 K.     

Neutron scattering studies of syndiotactic polystyrene crystals

Neutron scattering experiments are reported on solution grown crystals of syndiotactic polystyrene (sPS) at small and large q, in order to investigate the chain conformation within the lamellar crystals. From the results in both the Guinier and the intermediate ranges, we come to the following conclusions: The chain folds in one or several sheet depending on the molecular weight, comparison between measured and calculated intensity plots give strong indication that a is the fold direction. The statistical model recently built for the spatial arrangement of stems in a sheet-like structure is successful again, and demonstrate a strong statistical preference for adjacent re-entry.     

Neutron powder diffraction study of tetragonal crystal structures of cerium-neodymium dicarbides

The three ternary cerium-neodymium dicarbides Ce_xNd_1−xC₂ (x = 0.25, 0.50, 0.75) and the two binary dicarbides CeC₂ and NdC₂ have been prepared and their room temperature crystal structures examined by neutron powder diffraction by the Rietveld profile analysis method. The five compounds are isostructural, with tetragonal unit cell dimensions changing monotonically over the range a = 3.881(2), c = 6.487(3) Å to a = 3.827(2), c = 6.407(2) Å and they contain discrete acetylenic CC groups with carbon-carbon bond lengths close to 1.29(1) Å.     

Experimental evaluation of uranium ion signal intensity enhancement of TIMS using graphite powder deposition on uranium samples

Journal of Radioanalytical and Nuclear Chemistry - This study shows that the effectiveness of ultra-trace-level uranium isotopic analysis by thermal ionization mass spectrometry can be increased by...