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23 items found (0 items not approved), displaying 21 to 23.[First/Prev] 1, 2, 3 [Next/Last]

Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS I22-Small angle scattering & Diffraction	Formation of stable uranium(VI) colloidal nanoparticles in conditions relevant to radioactive waste disposal Pieter Bots , Katherine Morris , Rosemary Hibberd , Gareth Law , Fred Mosselmans , Andy Brown , James Doutch , Andy Smith , Sam Shaw Langmuir 30 (48) DOI: 10.1021/la502832j Diamond Proposal Number(s): [5975, 8544] Open Access Show Abstract ▼ Abstract: The favored pathway for disposal of higher activity radioactive wastes is via deep geological disposal. Many geological disposal facility designs include cement in their engineering design. Over the long term, interaction of groundwater with the cement and waste will form a plume of a hyperalkaline leachate (pH 10–13), and the behavior of radionuclides needs to be constrained under these extreme conditions to minimize the environmental hazard from the wastes. For uranium, a key component of many radioactive wastes, thermodynamic modeling predicts that, at high pH, U(VI) solubility will be very low (nM or lower) and controlled by equilibrium with solid phase alkali and alkaline-earth uranates. However, the formation of U(VI) colloids could potentially enhance the mobility of U(VI) under these conditions, and characterizing the potential for formation and medium-term stability of U(VI) colloids is important in underpinning our understanding of U behavior in waste disposal. Reflecting this, we applied conventional geochemical and microscopy techniques combined with synchrotron based in situ and ex situ X-ray techniques (small-angle X-ray scattering and X-ray adsorption spectroscopy (XAS)) to characterize colloidal U(VI) nanoparticles in a synthetic cement leachate (pH > 13) containing 4.2–252 μM U(VI). The results show that in cement leachates with 42 μM U(VI), colloids formed within hours and remained stable for several years. The colloids consisted of 1.5–1.8 nm nanoparticles with a proportion forming 20–60 nm aggregates. Using XAS and electron microscopy, we were able to determine that the colloidal nanoparticles had a clarkeite (sodium–uranate)-type crystallographic structure. The presented results have clear and hitherto unrecognized implications for the mobility of U(VI) in cementitious environments, in particular those associated with the geological disposal of nuclear waste.	Oct 2014
B21-High Throughput SAXS I22-Small angle scattering & Diffraction	The current status of small-angle X-ray scattering beamline at Diamond Light Source Katsuaki Inoue , James Doutch , Nicholas Terrill Bunseki Kagaku 62, 565-570 DOI: 10.2116/bunsekikagaku.62.565 Open Access Show Abstract ▼ Abstract: The small-angle X-ray scattering (SAXS) covers the major disciplines of biology, chemistry and physics delivering structural and dynamic information in nanoscience, mesoscopic architectures, supramolecular structures, and nucleation/growth of crystals. SAXS is also proving to be important in archaeological, environmental, and conservation sciences, and has further indicated its ability to span wide-ranging scientific disciplines. Thus, strong needs for SAXS studies are increasing significantly in a broad range of scientific fields year by year. Based on such a background, the demand for high throughput SAXS experiments is increasing. At the synchrotron facility, Diamond Light Source, one SAXS beamline, Non-crystalline diffraction I22 is now operational and highly automated throughput small-angle X-ray scattering (HATSAXS) beamline B21 is now under construction. I22 is the Undulator beamline and wide varieties of experiments, including time-resolved experiments are attempted. Based on the concept of HATSAXS, the key feature of B21 will focuses on the automation of end-station equipment. A automated sample changer has been purchased for solution SAXS measurements on biomolecules. A robotic-arm-type automated sample changer that is capable of handling several kinds of samples in material science is also being constructed. B21 is expected to successfully provide all users highly automated throughput measurements with the highest possible reliability and accuracy. Construction of this beamline will end in the second half of 2012, and will be open for users in the early summer of 2013 after commissioning.	Jun 2013
I02-Macromolecular Crystallography I03-Macromolecular Crystallography	Challenges of sulfur SAD phasing as a routine method in macromolecular crystallography James Doutch , Michael A. Hough , S. Samar Hasnain , Richard W. Strange Journal Of Synchrotron Radiation 19 (1), 19-29 DOI: 10.1107/S0909049511049004 PMID: 22186640 Show Abstract ▼ Abstract: The sulfur SAD phasing method allows the determination of protein structures de novo without reference to derivatives such as Se-methionine. The feasibility for routine automated sulfur SAD phasing using a number of current protein crystallography beamlines at several synchrotrons was examined using crystals of trimeric Achromobacter cycloclastes nitrite reductase (AcNiR), which contains a near average proportion of sulfur-containing residues and two Cu atoms per subunit. Experiments using X-ray wavelengths in the range 1.9-2.4 Å show that we are not yet at the level where sulfur SAD is routinely successful for automated structure solution and model building using existing beamlines and current software tools. On the other hand, experiments using the shortest X-ray wavelengths available on existing beamlines could be routinely exploited to solve and produce unbiased structural models using the similarly weak anomalous scattering signals from the intrinsic metal atoms in proteins. The comparison of long-wavelength phasing (the Bijvoet ratio for nine S atoms and two Cu atoms is ~1.25% at ~2 Å) and copper phasing (the Bijvoet ratio for two Cu atoms is 0.81% at ~0.75 Å) for AcNiR suggests that lower data multiplicity than is currently required for success should in general be possible for sulfur phasing if appropriate improvements to beamlines and data collection strategies can be implemented.	Dec 2011

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