An Australian research group has recently published experimentally obtained X-ray mass attenuation coefficients of zinc for 7.2- 15.2 keV X-rays with an absolute accuracy of 0.044% and 0.197%. For more information, see the paper, "X-ray mass attenuation coefficients and imaginary components of the atomic form factor of zinc over the energy range of 7.2.15.2 keV", N. A. Rae et al., Phys. Rev. A81, 022904 (2010).
Recently in Others Category
So far, it has been understood that the only way to realize hard-X-ray mirrors with near 100% reflectivity is the use of total external reflection at grazing incidence to a surface. Dr. Y. V. Shvyd'ko (Argonne National Lab,
Chandrayaan-1 was a lunar probe launched by the Indian Space Research Organization (ISRO). It was equipped with advanced X-ray spectrometers for investigation. After suffering from several technical problems including failure of the star sensors and insufficient thermal shielding, Chandrayaan stopped sending radio signals on August 29, 2009 shortly after which the ISRO officially declared the mission over. Chandrayaan operated for 312 days from October 2008. For more information, visit the Web page,http://www.isro.org/Chandrayaan/htmls/home.htm
At the Photon Factory, KEK, Japan , Dr. T. Okuda (University of Tokyo
It is well known that nanoparticles often enhance catalytic activity. However, it is still an open question as to whether the metallic or the oxidized state of the particle is the catalytically more active phase. It is therefore significant to study the oxidation/reduction process of metallic nanoparticles. A group led by Professor H. Dosh (Max-Planck-Institut für Metallforschung , Germany
Scanning diffraction microscopy, or ptychography, was first developed for the scanning transmission electron microscope (STEM). In the same way, by using an X-ray nano beam, one can use a STXM. The X-ray beam is focused onto the sample via a lens, and the transmission is measured. The image is obtained by plotting the transmission as a function of the sample position, as it is rastered across the beam. The analysis is straightforward, but its resolution is limited by the beam size. On the other hand, coherent diffractive imaging (CDI) now reaches resolutions below 10 nm, but the reconstruction procedures are not always easy due to the influences of data quality, sample conditions etc. A Swiss research group led by Drs. C. David and F. Pfeiffer (Paul Scherrer Institut) recently demonstrated a ptychographic imaging method that bridges the gap between STXM and CDI by measuring complete diffraction patterns at each point of a STXM scan. The group employed an advanced large-area pixel detector, Pilatus, to obtain the diffraction pattern efficiently. These diffraction data were then treated with an image reconstruction algorithm developed by the team. Several tens of thousands of diffraction images were processed to obtain one super-resolution X-ray image. The algorithm not only reconstructs the sample but also the exact shape of the light probe resulting from the X-ray beam. The 6.8 keV X-ray beam was focused using a zone plate, and the beam size was 300 nm. The spatial resolution achieved was about five times higher. For more information, see the paper, "High-Resolution Scanning X-ray Diffraction Microscopy", P. Thibault et al., Science, 321, 379 - 382 (2008).
Zeolites are microporous crystalline materials, and in the unit cell, the tetrahedrally coordinated Si and Al atoms occupy the so-called crystallographic T-sites. In addition to their pore size, Al's occupancy in the specific T-sites is extremely important in catalytic activity. So far, however, the distribution of Al has remained an unresolved problem. Recently, Professor J. A. van Bokhoven (ETH Zurich , Switzerland
At Brookhaven National Laboratory, United States, researchers have recently found a novel way to generate a very short controllable free electron laser (FEL) pulse, which usually depends on the length of the electron pulse. The main idea is the use of a Ti:Sapphire laser that combines a 150 femtosecond (FWHM) pulse of light with the much longer electron beam. This leads to a femtosecond FEL pulse that keeps growing in intensity and shortening in time duration, which is attributed to a phenomenon called superradiance (for details, see, R. H. Dicke, Phys. Rev. 93, 99 (1954)). The present research is the first to experimentally observe the effects of superradiance in a FEL setup. The output FEL pulse duration was measured to be as short as 81 femtoseconds, a roughly 50% reduction compared to the input seed laser. Understanding how to produce these intense, ultrafast pulses of light could help scientists around the world as they begin to construct the next generation of light source facilities. For more information, see the paper, "Experimental Characterization of Superradiance in a Single-Pass High-Gain Laser-Seeded Free-Electron Laser Amplifier ", T. Watanabe et al., Phys. Rev. Lett. 98, 034802 (2007).
In January 2006, the Stardust spacecraft brought back a number of tiny particles from comet Wild 2, which is believed to have originated within a cloud of comets just beyond the orbit of Neptune called the Kuiper Belt. The particles have been analyzed by X-rays at six synchrotron radiation facilities around the world, ESRF (France), APS (Argonne, USA), SSRL(Stanford, USA), ALS (Berkeley, USA), NSLS (Brookhaven, USA) and SPring-8 (Japan). The particles from this comet are important because they are believed to be close to the starting material of the solar system, which is now about 4.5 billion years old. The particles were found to contain a wide variety of minerals and organic materials that look similar to those seen in primitive meteorites found on earth, but the samples also revealed the presence of new materials not previously found in meteorites. It was also discovered that the samples contained minerals similar to Calcium Aluminum-rich inclusions (CAIs), which can be formed at high temperatures, i.e., in the innermost part of the solar nebula, well inside the orbit of Mercury. For more information on the Stardust mission, visit http://stardust.jpl.nasa.gov/home/index.html. Some interesting results have been published as part of a special series of papers in the Dec. 15, 2006, edition of the journal Science.
Professor Weckhuysen (Utrecht University, Netherlands) and his colleagues have recently solved the molecular mechanism for the organic-base-mediated synthesis of zeolites. AlPO4-5 is a typical zeolite, which can be constructed from aluminium-based tetrahedra (AlO4) and phosphorus-based tetrahedra (PO4). The research group compared the formation of the chargeless AlPO4-5 framework with the negatively charged framework (known as ZnAPO-34) that is formed by replacing Al3+ in AlPO4-5 with Zn2+. The former contains one-dimensional channels, but the latter spherical cavities rather than channels. By employing not only small and wide angle X-ray scattering (SAXS and WAXS), but also X-ray absorption spectroscopy, it was possible to observe in real time both the structural changes in the aluminophosphate gel and the conformational features of the organic base (tetraethylammonium hydroxide) used as a template for the crystallization of zeolite. The tetraethylammonium ion was found to form a complex with developing zeolite subunits in the gel, adopting a molecular structure close to that found in the final crystal. This molecular recognition process determines which type of crystal lattice is formed. The principal point here is that molecular organization takes place before crystallization. The experiments were done at BM26A, ESRF (Grenoble, France). For more information, see the paper, "A Combined SAXS/WAXS/XAFS Setup Capable of Observing Concurrent Changes Across the Nano-to-Micrometer Size Range in Inorganic Solid Crystallization Processes", A. M. Beale et al., J. Am. Chem. Soc., 128, 12386 (2006). Another interesting account can also be found in "Physical chemistry: Porous solids get organized", R. A. van Santen1, Nature, 444, 46 (2006).
The appearance of the ultimate X-ray microscope, with atomic-scale resolution and capable of seeing deep inside objects, has long been awaited. Professor I. Robinson (University College London, UK) and his team recently made a significant step towards realizing this dream, using the technique of coherent X-ray diffraction imaging, the possibility of which was first pointed out by Sayre (Acta Crystallogr. 5, 843 (1952)) but not demonstrated until 1999 by Miao et al (Nature 400, 342 (1999)). They observed the growth of nanometer-sized Pb crystals inside the vacuum chamber. The results showed that asymmetries in the diffraction pattern can be mapped to deformities, providing a detailed 3-D map of their location in the crystal. This new method shows that the interior structure of atomic displacements within single nanocrystals can be obtained by direct inversion of the diffraction pattern. The technique is an attractive alternative to electron microscopy because of the superior penetration of materials of interest by the electromagnetic waves, which are often less damaging to the sample than electrons. The experiments were done at beamline 34-ID-C at the Advanced Photon Source (APS) in the United States. For more information, see the paper, "Three-dimensional mapping of a deformation field inside a nanocrystal", Mark A. Pfeifer et al., Nature 442, 63 (2006).
Corrosion detracts some 3% from global GDP. From a positive point of view, however, chemical attack of metal surfaces may result in surface nano-structures with interesting technological applications such as catalysts and sensors. Professor H. Dosch (Max Planck Institute) and his colleagues have recently clarified a self-organization process on the surface of Cu3Au(111) single crystal alloy in a sulphuric acid solution, by means of a sophisticated X-ray diffraction technique with the aid of a brilliant synchrotron beam at ESRF, Grenoble, France. They observed many interesting phenomena. In the initial moments of corrosion, an extremely thin gold-rich layer, which had an unexpected crystalline and well-ordered structure, was formed. As the corrosion proceeded, this alloy layer was transformed into gold nano-islands of 20 to 1.5 nm. These islands eventually developed into a porous gold metal layer. For more information, see the paper, "Initial corrosion observed on the atomic scale", F. U. Renner et al., Nature, 439, 707-710 (2006).
The sketch for View on the Stour near Dedham, painted by Constable in 1822, has been analyzed by X-rays prior to Tate Britain's exhibition, Constable: the Great Landscapes, which opens on 1 June 2006. The sketch is the 4th of the 6 large River Stour paintings that Constable exhibited at the Royal Academy during 1819-1825. As with the other River Stour scenes, Constable made a preliminary full-scale compositional sketch in oils when planning the exhibition picture. The X-ray investigation clearly shows that the sketch originally included two boys fishing by the water's edge and a little girl close to one of the wooden beams marking the edge of a boat-building yard in the foreground. These figures were then painted out of the sketch by Constable and replaced by two young boys sitting on the edge of the river bank. In the finished exhibition painting, View on the Stour near Dedham, Constable altered the composition again and did not include the two boys from the sketch. X-ray analysis has successfully revealed a number of such alterations that are not visible on the surface of the work. For more information, contact Helen Beeckmans/Patricia O'Connor, Tate Press Office, Millbank, London SW1P 4RG, Phone: +44-20-7887-8730/32, Fax: +44-20-7887-8729, pressoffice@tate.org.uk
A team of scientists from the Technical University in Vienna, the Technical University in Berlin and the ESRF have combined tomography and diffraction using 80 keV X-rays to observe creep void evolution and the correlation to texture and microstructure development, which are important parameters for understanding the lifetime of components subjected to high temperature loading. The studies were carried out for a brass alloy, CuZn40Pb2, which contains three phases: -brass, s-brass, and Pb. They developed a specifically designed creep device in order to avoid artifacts during the tomography, and therefore the path of the incoming and the emerging X-rays over a complete 360 deg turn of the sample is identical. A tensile load of 25 MPa was applied by using a spring in order to avoid vibrations, and the sample was heated to 375 ºC by an induction-heated loop around the bottom of the sample. The results reveal that void growth versus time follows an exponential growth law and that the formation of large void volumes coincides with texture evolution and a steady state in the development of dislocation density. The in-situ determination of void evolution in bulk samples opens up new ways toward the assessment of creep damage to the strength of materials and subsequently towards lifetime predictions of samples and components subject to high temperature loading. For more information, see the paper, "Simultaneous Tomography and Diffraction Analysis of Creep Damage", A. Pyzalla et al., Science, 308, 92-95 (2005).
Super conducting devices are promising as high energy-resolution detectors for soft X-ray and/or mass spectrometry. As the device size is quite small, e.g., several hundred microns squared, arraying has been one of the most important technical targets for enhancing detection efficiency. So far, it has been difficult to increase the number of arrays, because of the incoming heat problem when connecting wires from devices operated at 0.3 K to electronic circuits at normal temperature. Dr. M. Ohkubo and his colleagues at the National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan recently succeeded in developing a novel technology using thin co-axis wires of 0.33mm in dia. They also attached great importance to material selection. As a result, it has become possible to connect more than 100 arrays, yet the incoming heat is extremely small at 5.4 x 10-6 W. The increase in temperature has effectively been suppressed to 15 mK. For more information, contact Dr. M. Ohkubo, Phone, +81-29-861-5685, Fax +81-29-861-5730, m.ohkubo@aist.go.jp, http://unit.aist.go.jp/riif/srg/index.htm
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