Comparing results of X-ray diffraction, µ-Raman spectroscopy and neutron diffraction when identifying chemical phases in seized nuclear material,during a comparative nuclear forensics exercise

Journal of Radioanalytical and Nuclear Chemistry - This work presents the results for identification of chemical phases obtained by several laboratories as a part of an international nuclear...     

Electric field effects on nuclear spin�Cspin coupling tensors and chiral discrimination via NMR spectroscopy

Nuclear magnetic resonance spectrometers presently available are unable to recognize the two mirror-image forms of a chiral molecule, because in the absence of a chiral solvent, the NMR spectral parameters (chemical shifts and spin?Cspin coupling constants) are identical for the two enantiomers. This paper discusses how chirality may nevertheless, at least in theory, be recognized in liquid-state NMR spectroscopy by applying strong d.c. electric fields and measuring a pseudoscalar contribution to nuclear spin?Cspin coupling polarizability. Calculations are reported for medium-size chiral molecules, (2R)-N-methyloxaziridine, (R _a )-1,3-dimethylallene, and (2R)-2-methyloxirane. The very small contributions provided by the pseudoscalar of nuclear spin?Cspin coupling polarizability seem rather difficult to detect via NMR experiments in disordered phase.     

Non-supercritically dried silica–silica composite aerogel and its possible application for confining simulated nuclear wastes

The simpler non-supercritical drying approach has been used for the first time for the preparation of silica–silica composite aerogels (CA) and the efficiency of the process being demonstrated by testing the use of the aerogels for simulated high level nuclear waste confinement. Compositions of 5, 10, 20, 30, 40 and 50 wt% of silica (aerosil® 380) in silica–aerogel were prepared by introducing pyrogenic silica in to silica sol derived by hydrolysis of Tetraethoxy silane (TEOS). The silica–silica composite aerogels (CA) possessed very high surface area and low bulk densities. The effectiveness of the prepared composite aerogels as precursor for high level nuclear waste immobilized glass is also presented. Neodymium nitrate dissolved in isopropanol is used to simulate +3 valent actinides. The stability of neodymium in the glass matrix has been found to be extremely high. Transmission electron microscopy (TEM) has been used to characterise the aerogels as well as neodymium incorporated sintered gels. X-ray diffraction (XRD) studies of the sintered samples reveal the formation of neodymium silicates.     

Effect of accelerators on thoria based nuclear fuels for rapid and quantitative pyrohydrolytic extraction of F? and Cl? and their simultaneous determination by ion chromatography

Pyrohydrolysis is a fast, reliable and convenient method for the decomposition of solid refractory samples. Thoria based mixed oxide nuclear fuels requires more than 1,200?°C reaction temperature to lose its structural integrity so as to release the halides. In the present paper, we report WO₃ accelerated pyrohydrolytic extraction technique for the separation of F^? and Cl^? from thoria based fuels along with the feasibility of using MoO₃ and V₂O₅. The mechanism of extraction has been investigated in detail using X-ray diffraction and recovery studies. ThO₂ along with its halides undergo high temperature solid state reaction with WO₃ forming Th(WO₄)₂ and releasing the halides for their subsequent hydrolysis. The quantification was carried out by ion chromatography with suppressed ion conductivity detection. The average recoveries of the spiked samples for F^? and Cl^? were 93?C99%. The method was successfully applied for simultaneous determination of F^? and Cl^? in thorium based nuclear fuel samples at 950?°C.     

Ab initio calculations of oxygen nuclear quadrupole coupling constants and oxygen and silicon NMR shielding constants in molecules containing SiO bonds

Ab initio coupled Hartree—Fock perturbation theory (CHFPT) calculations employing large gaussian basis sets have been used to evaluate the electric field gradient at O, q^o, and the NMR shieldings at O and Si, σ^o and σ^Si, in the molecules SiO, SiO₂, Si₂O₂, H₂SiO, SiO⁻⁴₄, Si(OH)₄ and (H₃Si)₂O. Species containing Si bonded to three or fewer atoms have small NMR shieldings at both O and Si while those with four-coordinate Si have systematically larger O and Si shieldings. A significant positive correlation is observed between calculated O and Si NMR shieldings. Reduction of the SiO distance in SiO⁴⁻₄ and H₃SiOSiH₃ gives a significant reduction in the magnitude of q^o and a small increase in σ. Anisotropies in σ^Si are large for two- and three-coordinate Si (200–900 ppm) but for (H₃Si)₂O the σ^Si anisotropy is only ≈60 ppm. Anisotropies in σ^o are generally larger than those in σ^Si, with values larger than 200 ppm for both SiO⁻⁴₄ and (H₃Si)₂O. Values of q^o for SiO⁴⁻₄ and (H₃Si)₂O are in qualitative agreement with experimentally determined values for nesosilicates and SiO₂ polymorphs, respectively, but all the q^o values appear to be exaggerated at the Hartree—Fock level. Also, q^o values are not greatly different for the exotic species SiO, Si₂O₂, etc. compared to the typical silicate models SiO⁴⁻₄ and (H₃Si)₂O. Calculated isotropic chemical shifts yield good values for the Si chemical shift differences of SiF₄, SiO⁴⁻₄ and (H₃Si)₂O and for the O chemical shift difference of SiO⁴⁻₄ and H₂O. For SiO⁴⁻₄ the paramagnetic contribution to the Si shift, σ^pSi is dominated by contributions from the t₂ symmetry SiO bonding orbital and σ^pO is dominated by contributions from the t₂ symmetry O 2p non-bonding orbital.     

Photonic Lab-on-a-Chip analytical systems for nuclear applications: optical performance and UV–Vis–IR material characterization after chemical exposure and gamma irradiation

Journal of Radioanalytical and Nuclear Chemistry - The use of microfluidics technology and the miniaturization of analytical techniques is of high interest for the chemical and nuclear industries....     

The effective nuclear charge model—IX. On the transferability of effective nuclear charges defined from homonuclear diatomic molecules

Effective nuclear charges of many triatomic molecules have been calculated inversely by the least squares method (Jacobian matrix method) from the experimental force constants which are determined by normal coordinate analyses using the observed vibrational data. The values of effective nuclear charges thus obtained are compared with those defined from homonuclear diatomic molecules. The results show that the transferability of effective nuclear charges from homonuclear diatomic molecules to triatomic molecules is moderately good. This gives support to the utility of the effective nuclear charge model.     

George de Hevesy (1885–1966): discoverer of hafnium,founder of radioanalytical chemistry and X-ray fluorescence analysis and father of nuclear medicine

George de Hevesy known as discoverer of hafnium, founder of radioanalytical chemistry and X-ray fluorescence analysis and father of nuclear medicine has done important research work in inorganic, physical and radioanalytical and physiological chemistry as well as in geochemistry, radiation biology and medicine. When he must flee for political reasons from a country he must change his colleagues, his equipments, and the topic of his work. It is extremely surprising that he could receive important results under such circumstances even at an advanced age.     

13C nuclear magnetic resonance spectroscopy and lifetime studies of the solution photoreactivity of 1,4-bis(β-pyridyl-2-vinyl)benzene and 2,5-distyrylpyrazine

The photoreactivity of 1,4-bis(β-pyridyl-2-vinyl)benzene and distyryl-pyrazine has been investigated using lifetime, Shpol'skii and carbon-13 nuclear magnetic resonance (¹³C NMR) techniques. Our study shows that long-lived emitting species exist in concentrated solutions indicating excited state aggregation that could lead to bimolecular processes in concentrated solutions. It is confirmed that the photoproducts do not emit in the spectral region studied by using the Shpol'skii technique.¹³C NMR has been performed only for concentrated solutions, revealing the formation of cis isomers in addition to the occurrence of the previously reported photochemical processes.     

The surface characterization and corrosion resistance of 11 % Cr ferritic/martensitic and 9–15 % Cr ODS steels for nuclear fuel reprocessing application

In spent fuel nuclear reprocessing plant, nitric acid is the main medium used in PUREX method. The passive film compositions and corrosion resistance of 11 % Cr ferritic/martensitic and 9–15 % Cr oxide dispersion strengthened steels in different nitric acid concentrations were studied. The open circuit potential is shifted toward more noble potential as the concentrations increased from 1 M HNO₃ to 9 M HNO₃ in all the investigated alloy steels. The results of the potentiodynamic polarization plots also exhibited a shift in corrosion potential as the concentrations increased from 1 M to 9 M HNO_3. This shift is undesirable because of risk of overshooting the potential beyond passive region and may result into transpassive corrosion. The X-ray photoelectron spectroscopy results of the passive film analysis are composed mostly of Fe₂O₃, Cr₂O₃, and Y₂O₃, and the depth profile of Fe and Cr concentrations vary depending upon the nitric acid concentration. The surface morphology after the corrosion test does not show intergranular corrosion attack at the nitric acid concentrations studied. It is desirable that materials for use in nitric acid service are resistant to such corrosion induced degradation.     

A future for nuclear analytical techniques? Why not?

The choices of universities and national research institutions in supporting scientific research are increasingly justified on the basis of, amongst others, the relevance that has to be reflected by external, preferably sustainable funding of the research programs. Many traditional fields of application such as environmental sciences do not offer a promising outlook in this respect. As a consequence, university research reactors face closure because of reallocations of university funds to more contemporary sciences such as molecular biology and nanotechnology. Therefore, laboratories operating nuclear analytical techniques (NAA, (TR)XRF, and PIXE) need to use their creativity in finding ways for participation in, for example, nanotechnology, cancer research, or genomics. This requires an open mind in terms of the opportunities, strengths, and weaknesses of the techniques, and a departure of technique-oriented research towards problem-oriented research in which other nuclear techniques can be used. The unique features of radiotracers, nuclear imaging, and nuclear beam techniques are discussed in view of the new areas mentioned above. Some examples of opportunities for nuclear analytical techniques in the above-mentioned fields are given.     

LCAO Xα calculations of nuclear magnetic shielding in molecules

On the basis of the four-current density functional formalism, a method to calculate chemical shifts is developed, allowing the use of Xα wavefunctions in computations of magnetic properties of molecules. First results of calculated nuclear magnetic shielding constants and diamagnetic susceptibilities in small molecules using a LCAO Xα scheme within a minimal basis set are presented and compared with values obtained by CHF, UCHF, and FPT methods and with experiment. The CHF results show better agreement with experiment than our calculations, but our results are of the quality of UCHF data.     

The role sol–gel process for nuclear fuels-an overview

The paper reviews the sol–gel methods used for the preparation of nuclear fuel materials in the form of microspheres. It also discusses how these microspheres can be fabricated into nuclear fuels for reactors such as High Temperature Gas Cooled Reactors and Fast Reactors. The performance of these microsphere-based fuels is reviewed. More recent applications, such as the transmutation of minor actinides, (Np, Am and Cm) and hydrogen production, are also briefly covered.     

Ab initio study of the nuclear spin—spin coupling constants and magnetic shielding constants in silicon derivatives via the equations-of-motion method

Non-empirical equations-of-motion calculations of the nuclear spin—spin coupling constants and magnetic shielding constants in a representative series of molecules featuring siliconsilicon or siliconcarbon single, double and triple bonds are presented. The EOM results, which include the main portion of the electron correlation effects, are in resonable agreement with the available experimental data. On passing from single to double and triple bonding situation the pattern for the ¹J(SiY) parameters resembles that exhibited by ¹J(CY) in the structurally related carbocompounds, whereas an inversion in the relative position of the triply bonded atom is predicted in the case of the ²⁹Si resonance relative to the ¹³C sequence.