October 2009 Archives

One of the most important applications of X-ray spectroscopy is chemical state analysis. A research group led by Dr. M. Jaksic (Rudjer Boskovic Institute, Croatia) has recently reported chemical effects observed in high resolution Kβ spectra of Ti oxides and other compounds in the case of 2 MeV proton excitation. In addition to the determination of the oxidation number by the energy differences between Kβ_1,3 and Kβ₅, the sum of the relative intensities of Kβ_2,5 and Kβ" can give information on the length of chemical bonds. The influence of self-absorption for thick samples on X-ray spectra is also discussed. For more information, see the paper, "Chemical effects on the Kβ" and Kβ_2,5 X-ray lines of titanium and its compounds", L. Mandic et al., Phys. Rev. A80, 042519 (2009). Readers might be also interested in the recent synchrotron radiation studies on Ti oxides and other compounds reported by Dr. B. Beckoff's group (PTB, Germany), "Evaluation of high-resolution X-ray absorption and emission spectroscopy for the chemical speciation of binary titanium compounds", F. Reinhardt et al., Anal. Chem. 81, 1770 (2009).

X-ray absorption microscopy is simple, but has low sensitivity in biological samples that are made of light elements. X-ray phase contrast imaging can provide contrast that is 3 orders of magnitude greater than X-ray absorption. However, phase contrast imaging has not been that widely used so far mainly because of the unusual requirements of the experimental setup. Dr. W. Yashiro (The University of Tokyo, Japan) and his colleagues have recently proposed a novel setup that is feasible. The research group simply added a transmission grating to the setup for conventional X-ray absorption microscopy with a Fresnel Zone Plate (FZP) objective lens. Because of the self-imaging phenomenon in Talbot effects, a phase difference image can be produced by the transmission grating placed at the downstream of the back focus of the FZP. The experiment was done at beamline BL20XU, SPring-8. For more information, see the paper, "Hard-X-Ray Phase-Difference Microscopy Using a Fresnel Zone Plate and a Transmission Grating", W. Yashiro et al., Phys. Rev. Lett. 103, 180801 (2009).

A recent edition of Nature News featured the international race to build X-ray free electron laser facilities. At the Linac Coherent Light Source (LCLS), Stanford, USA, scientists have succeeded in lasing 8 keV X-rays and started to use them in their research since April, this year (2009). Meanwhile, soft X-ray laser FLASH, which is a pilot facility for XFEL at the European X-Ray Free-Electron Laser (XFEL), Hamburg, Germany, has been open for scientific use since 2005, and the main XFEL will be completed in 2014. Nature News interviewed various people both in Stanford (Joachim Stohr, Jerome Hastings and John Bozek) and Hamburg (Heinz Graafsma, Helmut Dosch and Massimo Altarelli). For more information, see the article, "X-ray free-electron lasers fire up", Eric Hand, Nature 461, 708-709 (2009).