June 2011 Archives

The European XFEL under construction at Hamburg in Germany aims to have the first beam ready in 2015. Very recently, it was found that the design parameters can be further improved. The first revision is to the energy range. This will now be 260 eV - 25 keV, while the 2006 design was 800 eV - 12.4 keV. The second is X-ray pulse duration. This will become of variable duration from a few femtoseconds (fs) to about 100 fs, instead of about 100 fs only. Such upgrades will be realized by improving electron beam quality by building on the experience with the X-ray free-electron laser at Stanford. For further information, visit the Web page, http://www.xfel.eu/news/2011/x_ray_flashes_revised/

Professor K. F. Ludwig (Boston University, USA) and his colleagues have recently reported their real-time X-ray scattering studies on heterogeneous microscale dynamics in the martensitic phase transition of cobalt. During the transformation of the high-temperature fcc phase to the low-temperature hcp phase, first, a rapid local transformation happens, and then, strains are relaxed slowly. The research group employed coherent X-ray scattering measurements to see the latter part of the transformation. It was found that the kinetics is dominated by discontinuous sudden changes - avalanches. The spatial size of observed avalanches varies widely, from 100 nm to 10μm, the size of the X-ray beam. For more information, see the paper, "Direct Measurement of Microstructural Avalanches during the Martensitic Transition of Cobalt Using Coherent X-Ray Scattering", C. Sanborn et al., Phys. Rev. Lett. 107, 015702 (2011).

The Dead Sea Scrolls are a collection of 972 texts from the Hebrew Bible and extra-biblical documents found between 1947 and 1956 at Khirbet Qumran on the northwest shore of the Dead Sea from which it derives its name, in the British Mandate for Palestine, in what is now named the West Bank. Recently, a research group led by Professor B. Kanngiesser (Technische Universität Berlin, Germany) has investigated the feasibility of merging two X-ray techniques, ordinary micro XRF and confocal 3D micro XRF for optimized analysis of highly inhomogeneous samples such as the Dead Sea Scrolls. Ordinary micro XRF lacks information on the depth, but the measurement is efficient and rather quick. On the other hand, confocal 3D micro XRF has depth resolution, but the measurement takes very long. The authors found that the reliability of the analysis of highly heterogeneous samples can be improved by quantitatively combining both data. For more information, see the paper, "3D Micro-XRF for Cultural Heritage Objects: New Analysis Strategies for the Investigation of the Dead Sea Scrolls", I. Mantouvalou et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac2011262 Publication Date (Web): June 29, 2011).

A research group led by Professor L. Vincze (Ghent University, Belgium) has recently reported the interesting analysis of 1-20 μm sized inclusions in natural diamond crystals from Rio Soriso (Juina area, Mato Grosso State, Brazil). The crystals are called ultra-deep diamond, because they were formed in the astenospheric upper mantle, the transition zone (410-670 km), and even the lower mantle (>670 km) of the Earth. The experiment is basically 3D imaging by confocal X-ray fluorescence suing synchrotron radiation. By scanning X-ray energy near the Mn and Fe K absorption edges, the authors obtained chemical information on the inclusion cloud in the crystal. It was found that the observed Fe-rich inclusions were ferropericlase (Fe,Mg)O, hematite and a mixture of these two minerals. Another finding was that significant overprint of inclusions along pre-existing planar features is possible without changing their outer shape. For more information, see the paper, "Three-Dimensional Fe Speciation of an Inclusion Cloud within an Ultradeep Diamond by Confocal μ-X-ray Absorption Near Edge Structure: Evidence for Late Stage Overprint", G. Silversmit et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac201073s Publication Date (Web): June 27, 2011).

Ptychographic X-ray diffraction microscopy is known as an extension of so-called X-ray diffraction microscopy, which is a lensless X-ray imaging technique based on coherent diffraction measurements and iterative phasing methods. The technique employs sample scanning to see a large viewing area, but so far, the spatial resolution has been rather limited mainly because of positioning errors due to the drift between the sample and illumination optics. Recently, Professor Y. Takahashi (Osaka University, Japan) and his colleagues have published an experimental way to resolve the problem. The research group has developed a method of correcting positioning errors, and made it possible to illuminate a highly focused hard X-ray beam at the exact position on the samples. The spatial resolution achieved is as good as 10 nm or even better in a viewing area of larger than 5 μm. For more information, see the paper, "Towards high-resolution ptychographic X-ray diffraction microscopy", Y. Takahashi et al., Phys. Rev. B83, 214109 (2011).

When laser light hits thin solid foil, one can obtain soft X-rays, and this is sometimes called a laser plasma X-ray source. When the peak power of the laser becomes extremely high by shortening the pulse duration, it is also possible to observe hard X-ray spectra including Kα and Kβ emission. A team at Sandia National Laboratory has recently reported some calculations on the efficiency of Kα emission. The conversion efficiency of laser energy into Kα X-ray energy is clearly a critical parameter for designing an X-ray source. Basically the value is fairly small, but the team's simulations indicate that an enhancement of efficiency greater than tenfold over conventional single targets may be possible by introducing a two-phase target concept. For more information, see the paper, "Efficiency Enhancement for Kα X-Ray Yields from Laser-Driven Relativistic Electrons in Solids", A. B. Sefkow et al., Phys. Rev. Lett. 106, 235002 (2011).