April 2011 Archives

The International Union of Crystallography (IUCr) has announced that Professor E. Dodson (Department of Chemistry, University of York, UK), Professor C. Giacovazzo (Institute of Crystallography-CNR, Bari, Italy) and Professor G.M. Sheldrick (Lehrstuhl fur Strukturchemie, Gottingen, Germany) have been awarded the ninth Ewald Prize for the enormous impact they have made on structural crystallography by designing new methods and providing these in algorithms and constantly maintained, renewed and extended user software. Their invaluable contributions to the computational side of the field have led to leadership with the program suites CCP4, SIR and SHELX, respectively. The presentation of the prize will be made during the Madrid Congress Opening Ceremony in August 2011. The Ewald Prize consists of a medal, a certificate and an award of USD 30,000. Former recipients are D. Sayre (USA, 2008), P. Coppens (USA, 2005), M. M. Woolfson (UK, 2002), G. N. Ramachandran (India, 1999), M. G. Rossmann (USA, 1996), N. Kato (Japan, 1993), B. K. Vainshtein (Russia, 1990), J. M. Cowley (USA) and A. F. Moodie (Australia) in 1987.

Phase contrast X-ray imaging is a promising method for low Z samples which cannot always be properly imaged by conventional absorption and scattering imaging. Recently Professor R. D. Speller (University College London) and his colleagues reported a novel way using a laboratory X-ray source outfitted with a pair of coded apertures; one in front of the sample for imaging and one behind it. They were offset slightly to remove scattering background. Readers might be aware that the method is quite similar to X-ray Talbot interferometry (for example, see the previous news article, "Micro-structure imaging using visibility contrast", No.5, Vol. 39 (2010)), when a 2D grating is used as a coded-aperture. The technique could open up many interesting opportunities through its application to a wide range of fields, such as nano-bio technologies, because the experiments can be done with an ordinary incoherent X-ray source. For more information, see the paper, "Noninterferometric phase-contrast images obtained with incoherent x-ray sources", A. Olivo et al., Appl. Optics, 50, 1765 (2011).

In most cases, rocks and geomaterials are chemically and structurally inhomogeneous. The use of X-ray absorption spectro-microscopy is one promising solution, but the very long measuring time for scanning large samples with a tiny beam poses a limit for detailed analysis. At the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, scientists recently performed much more efficient and feasible experiments by coupling near-edge X-ray absorption spectroscopy and full-field transmission radiography with a large X-ray beam. The method basically consists of the repeated acquisition of X-ray images as a function of X-ray energy near the absorption edge (in the present case, iron K edge). The research group also combines this with polarization contrast imaging. By looking at the Fe³⁺/Fe(total) image, some redox variations were found in the single mineralogical phase of complex metamorphic rocks. The research group also analyzed bentonite analogue by separating the spectra into those of 5 simple minerals. The material is a candidate for the storage of nuclear waste and CO₂, and the information is helpful in designing such applications. For more information, see the paper, "Submicrometer Hyperspectral X-ray Imaging of Heterogeneous Rocks and Geomaterials: Applications at the Fe K-Edge", V. De Andrade et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac200559r Publication Date (Web) April 18, 2011).

A group led by Professor C. Chang (University of Pennsylvania, USA) has recently reported a quantitative X-ray phase imaging method that can be readily implemented on existing facilities. This technique utilizes Fresnel zone plates both as imaging optical elements for magnification and as second-order grating structures for phase-shifting interferometry. For more information, see the paper, "Quantitative x-ray differential-interference-contrast microscopy with independently adjustable bias and shear", T. Nakamura et al., Phys. Rev. A83, 043808 (2011).

A German group led by Professor U. Panne (Humboldt University, Berlin) has recently reported the successful application of the micro X-ray diffraction technique to the evaluation of the durability of cements against reaction with sodium sulfate. The experiments were done with a Debye-Scherrer camera equipped with a large-size CCD camera (3072×3072) and monochromatic micro beam (11.6 keV, 10 μm). By moving the sample along the X-ray path, it is possible to obtain information at different depths, and the team could therefore eventually reconstruct the profile of each crystalline phase along the depth from the surface. It was found that phase transformations proceeded during damage caused by penetration of sulfates. For more information, see the paper, "Deciphering the Sulfate Attack of Cementitious Materials by High-Resolution Micro-X-ray Diffraction", M. C. Schlegel et al., Anal. Chem., 83, 3744 (2011).

Recently, a research group led by Professor N. Kallithrakas-Kontos (Technical University of Crete, Greece) reported successful total-reflection X-ray fluorescence (TXRF) analysis of perchlorate. In the present research, perchlorate anions were concentrated on anion-selective membranes prepared on a mirror-polished quartz substrate. Then the quartz reflectors were taken out of the solution and analyzed by measuring Cl Kα intensity under the total-reflection condition, using a copper X-ray tube and helium atmosphere. The effects of many experimental parameters were discussed in detail, and even the possible capability of discrimination between chloride and perchlorate anions was suggested. The minimum detection limit was lower than 1 ng/mL. For more information, see the paper, "Determination of Trace Perchlorate Concentrations by Anion-Selective Membranes and Total Reflection X-ray Fluorescence Analysis", V. S. Hatzistavros et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac103295a Publication Date (Web): April 4, 2011).