High Energy Synchrotron Source Research Articles

Spectroscopic Methods in Mineralogy and Materials Sciences

(RIMG vol.78), Grant S. Henderson, Daniel R. Neuville and Robert T. Downs, editors. (2014) Reviews in Mineralogy and Geochemistry, i–xvii + 569 pages. ISBN 0-939950-84-7; ISBN13 978-0-939950-84-3. http://www.minsocam.org/MSA/RIM/rim78.html Spectroscopic techniques for mineralogical analysis are expanding and improving at an extremely rapid pace. Spectroscopic Methods in Mineralogy and Materials Sciences builds on the foundation presented by its predecessor, Reviews in Mineralogy Vol. 18, Spectroscopic Methods in Mineralogy and Geology , presenting both new techniques and updates to some of those presented in the earlier volume. As a whole, the volume is well organized and related chapters by different authors cross-reference one another, providing complementary information without duplicating background information. Most of the chapters provide an overview of the fundamental physics exploited by their respective techniques, the benefits and limitations, and examples of geological problems to which the techniques are applicable. Thus, this book should be helpful both as a general introduction to the array of spectroscopic methods available to mineralogists and materials scientists and as a more rigorous reference volume describing different techniques for those seeking to address a specific scientific problem. Like many of the other RIMG volumes, Spectroscopic Methods in Mineralogy and Materials Sciences is a valuable resource for graduate students and experienced researchers alike. The volume begins with a series of chapters on X-ray techniques. Chapter 1 introduces X-ray diffraction theory, including the characteristics and advantages of different types of X-ray sources available, from lower energy sources used in local laboratories through high-energy synchrotron sources. This general information provides a foundation for both the X-ray diffraction techniques described in this chapter, as well as for later chapters that focus on different X-ray techniques. It goes on to explain the different methods available …

Crambin - record in crystallographic resolution for a biological macromolecule

A couple of years ago a study was presented that set the record for the highest X-ray crystallographic resolution for a biological macromolecule [1]. The structure of the small protein crambin was determined to 0.48 Å resolution - this almost doubled the amount of available experimental data. Crambin is a small protein consisting of 46 amino acids belonging to the thionin family. Although the protein and its structure has long been known, it lacks any obvious enzymatic activity and has a hard-to-guess biological function. The protein crystallizes readily and serves as an excellent specimen for exploring the limits of resolution of the diffraction. The results demonstrated the possibilities that can be offered by a high-energy synchrotron source. The structure refined with Refmac, Shelxl and Mopro revealed a wealth of details. Bonding electron density became visible along the main chain. However, no fundamental additional structural features could be detected in comparison to the previously collected data set to 0.54 Å resolution. The availability of extremely high-resolution data is certainly of great help to drive further software development and methods for data interpretation. The question will always remain as to what the true limits are in terms of what can be seen in a biological macromolecule. Here we will present the results of our recent efforts in interpretation of such ultra-high resolution data.

Comparative study of X-ray charge-density data on CoSb3

CoSb3 is an example of a highly challenging case for experimental charge-density analysis due to the heavy elements (suitability factor of ~0.01), the perfect crystallinity and the high symmetry of the compound. It is part of a family of host-guest structures that are potential candidates for use as high-performance thermoelectric materials. Obtaining and analysing accurate charge densities of the undoped host structure potentially can improve the understanding of the thermoelectric properties of this family of materials. In a previous study, analysis of the electron density gave a picture of covalent Co-Sb and Sb-Sb interactions together with relatively low atomic charges based on state-of-the-art experimental and theoretical data. In the current study, several experimental X-ray diffraction data sets collected on the empty CoSb3 framework are compared in order to probe the experimental requirements for obtaining data of high enough quality for charge-density analysis even in the case of very unsuitable crystals. Furthermore, the quality of the experimental structure factors is tested by comparison with theoretical structure factors obtained from periodic DFT calculations. The results clearly show that, in the current study, the data collected on high-intensity, high-energy synchrotron sources and very small crystals are superior to data collected at conventional sources, and in fact necessary for a meaningful charge-density study, primarily due to greatly diminished effects of extinction and absorption which are difficult to correct for with sufficient accuracy.

Effects of mechanical grinding and low temperature annealing on crystal structure of Er5Si4

The effect of mechanical grinding and subsequent low temperature annealing on the orthorhombic to monoclinic structural transition in the Er5Si4 compound was studied by X-ray powder diffraction using both a conventional laboratory Cu Kα1 radiation and a high-energy synchrotron source. A reversible phase transition from the orthorhombic to monoclinic structure occurs as a result of mechanical grinding. Low temperature annealing reverses the transformation and converts the formed monoclinic phase back to the orthorhombic, evidently by relieving residual stress introduced during the grinding.

Synchrotron strain scanning for residual stress measurement in cold-drawn steel rods

Cold-drawn steel rods and wires retain significant residual stresses as a consequence of the manufacturing process. These residual stresses are known to be detrimental for the mechanical properties of the wires and their durability in aggressive environments. Steel makers are aware of the problem and have developed post-drawing processes to try and reduce the residual stresses on the wires. The present authors have studied this problem for a number of years and have performed a detailed characterization of the residual stress state inside cold-drawn rods, including both experimental and numerical techniques. High-energy synchrotron sources have been particularly useful for this research. The results have shown how residual stresses evolve as a consequence of cold-drawing and how they change with subsequent post-drawing treatments. The authors have been able to measure for the first time a complete residual strain profile along the diameter in both phases (ferrite and cementite) of a cold-drawn steel rod.

Thermal Fractionation and Isothermal Crystallization of Polyethylene Nanocomposites Prepared by in Situ Polymerization

Nanocomposites of high-density polyethylene (HDPE) and carbon nanotubes (CNT) of different geometries (single wall, double wall, and multiwall; SWNT, DWNT, and MWNT) were prepared by in situ polymerization of ethylene on CNT whose surface had been previously treated with a metallocene catalytic system. In this work, we have studied the effects of applying the successive self-nucleation and annealing thermal fractionation technique (SSA) to the nanocomposites and have also determined the influence of composition and type of CNT on the isothermal crystallization behavior of the HDPE. SSA results indicate that all types of CNT induce the formation of a population of thicker lamellar crystals that melt at higher temperatures as compared to the crystals formed in neat HDPE prepared under the same catalytic and polymerization conditions and subjected to the same SSA treatment. Furthermore, the peculiar morphology induced by the CNT on the HDPE matrix allows the resolution of thermal fractionation to be much better. The isothermal crystallization results indicated that the strong nucleation effect caused by CNT reduced the supercooling needed for crystallization. The interaction between the HDPE chains and the surface of the CNT is probably very strong as judged by the results obtained, even though it is only physical in nature. When the total crystallinity achieved during isothermal crystallization is considered as a function of CNT content, it was found that a competition between nucleation and topological confinement could account for the results. At low CNT content the crystallinity increases (because of the nucleating effect of CNT on HDPE), however, at higher CNT content there is a dramatic reduction in crystallinity reflecting the increased confinement experienced by the HDPE chains at the interfaces which are extremely large in these nanocomposites. Another consequence of these strong interactions is the remarkable decrease in Avrami index as CNT content increases. When the Avrami index reduces to 1 or lower, nucleation dominates the overall kinetics as a consequence of confinement effects. Wide-angle X-ray experiments were performed at a high-energy synchrotron source and demonstrated that no change in the orthorhombic unit cell of HDPE occurred during crystallization with or without CNT.

Compressibility of Lattice Parameters of Several LayeredCompounds

The lattice parameters of AlB2, MgB2 and TiB2 under pressures aredetermined with a high-energy synchrotron source in a diamond anvilcell. The experimental results indicate that these three compounds havedifferent mechanical behaviour under pressures, TiB2 is the hardest andMgB2 is the softest among the three materials. The phenomena areexplained in terms of bonding strength in the crystal. Our results maybe helpful for understating the decrease of the superconductingtransition temperature of MgB2 under pressures.

Specific chemical and structural damage to proteins produced by synchrotron radiation

Radiation damage is an inherent problem in x-ray crystallography. It usually is presumed to be nonspecific and manifested as a gradual decay in the overall quality of data obtained for a given crystal as data collection proceeds. Based on third-generation synchrotron x-ray data, collected at cryogenic temperatures, we show for the enzymes Torpedo californica acetylcholinesterase and hen egg white lysozyme that synchrotron radiation also can cause highly specific damage. Disulfide bridges break, and carboxyl groups of acidic residues lose their definition. Highly exposed carboxyls, and those in the active site of both enzymes, appear particularly susceptible. The catalytic triad residue, His-440, in acetylcholinesterase, also appears to be much more sensitive to radiation damage than other histidine residues. Our findings have direct practical implications for routine x-ray data collection at high-energy synchrotron sources. Furthermore, they provide a direct approach for studying the radiation chemistry of proteins and nucleic acids at a detailed, structural level and also may yield information concerning putative "weak links" in a given biological macromolecule, which may be of structural and functional significance.

X-ray generated ultrasound

This letter describes the first observations of x-ray generated ultrasonic signals in materials. The x rays used were the pulsed x-ray beams of continuous energy spectrum taken from a high-energy synchrotron source. The ultrasonic signals were detected with conventional piezoelectric transducers attached to stainless steel specimens.