October 2012 Archives

Professor Chi-Chang Kao has been named as the fifth director of the SLAC National Accelerator Laboratory, USA, which is one of the world's largest facilities for experimental particle physics. This reflects its change of mission from a dedicated particle physics lab to a multipurpose laboratory with an emphasis on X-ray studies. Similar policy can be a world trend - at DESY, Germany, Prof. Helmut Dosch, who is a world leader in X-ray surface physics and condensed matter physics, has already been a director since 2009. For more information, visit the Web page,

http://www6.slac.stanford.edu/news/2012-10-24-DirectAnnounce-CCK.aspx

Scientists at the National Institute of Standards and Technology, USA, have recently discussed some fundamental problems in quantitative electron probe X-ray micro analysis (EPMA). The main arguments center on two significant sources of uncertainty in the quantitative matrix correction models; the mass absorption coefficient and the backscatter coefficient. For more information, see the paper, "Uncertainty Estimates for Electron Probe X.ray Microanalysis Measurements", N. W. M. Ritchie et al., Anal. Chem., Article ASAP, Publication Date (Web): 22 Oct 2012.

A research team led by Professor K. Janssens (Antwerp University, Belgium) has published several interesting results from their series of analytical work on Van Gogh's paintings. They were able to give more detailed insights on the chemical forms of cadmium yellow and chromium yellow, as well as the role of lead in the pigment. For more information, see the following 3 papers, "Combined use of Synchrotron Radiation Based Micro-X-ray Fluorescence, Micro-X-ray Diffraction, Micro-X-ray Absorption Near-Edge, and Micro-Fourier Transform Infrared Spectroscopies for Revealing an Alternative Degradation Pathway of the Pigment Cadmium Yellow in a Painting by Van Gogh", G. Van der Snickt et al., Anal. Chem., Article ASAP, Publication Date (Web): 30 Aug 2012., "The Degradation Process of Lead Chromate in paintings by Vincent van Gogh studied by means of Spectromicroscopic methods. Part III: Synthesis, characterization and detection of different crystal forms of the chrome yellow pigment", L. Monico et al., Anal. Chem., Just Accepted Manuscript. Publication Date (Web): 10 Oct 2012, and "The Degradation Process of Lead Chromate in paintings by Vincent van Gogh studied by means of Spectromicroscopic methods. Part IV: Artificial ageing of model samples of co-precipitates of lead chromate and lead sulfate", L. Monico et al., Anal. Chem., Just Accepted Manuscript. Publication Date (Web): 10 Oct 2012.

One of the remarkable instances of progress in soft-X-ray spectroscopy recently is the successful high-resolution measurement of O-K edge absorption spectra of liquid water and ice, which have some disordered hydrogen-bonds. Professor R. Car (Princeton University) and his colleagues have recently reported their theoretical studies into the quantum dynamics of the nuclei and inhomogeneous screening effects. They found that the inclusion of quantum disorder is essential to bring the calculated spectra in close agreement with the experiment. In particular, the intensity of the pre-edge feature, a spectral signature of broken and distorted hydrogen bonds, is accurately reproduced, in water and hexagonal ice, only when quantum nuclei are considered. The effect of the inhomogeneous screening is less important but non-negligible, particularly in ice. For more information, see the paper, "Roles of quantum nuclei and inhomogeneous screening in the x-ray absorption spectra of water and ice", L. Kong et al., Phys. Rev. B86, 134203 (2012).

An Argentinean group has reported the experimental determination of cross sections for K-shell ionization by electron impact for Al, Si, and Ti and their oxides deposited on carbon substrates, for incident energies between 2.5 and 25 keV. For more information, see the paper, "Experimental determination of cross sections for K-shell ionization by electron impact for C, O, Al, Si, and Ti", S. P. Limandri et al., Phys. Rev. A86, 042701 (2012).