March 2011 Archives

RIKEN and the Japan Synchrotron Radiation Research Institute (JASRI) have announced the start-up of the X-ray Free Electron Laser (XFEL) facility in Harima, named "SACLA" (SPring-8 Angstrom Compact Free Electron Laser). For further information, visit the Web page, http://xfel.riken.jp/eng/index.html

A Japanese group led by Professor K. Tsuji (Osaka City University, Japan) recently reported an interesting application of 3D micro X-ray fluorescence (XRF) imaging. One should note that their research employed low-power laboratory X-ray sources (30-50W, Mo tube) instead of synchrotron X-rays. They also used two polycapillary lenses for both incoming and outgoing directions to limit the viewing volume in 3D. The research group measured some forensic samples such as multilayered automotive paint fragments, leather samples etc., which have different color coatings. They analyzed 3D profiles of many elements (Si, S, Cl, K, Ca, Ti, Mn, Fe, Zn, and Ba) and discussed the relationship with the coating. For more information, see the paper, "Depth Elemental Imaging of Forensic Samples by Confocal micro-XRF Method", K. Nakano et al., Anal. Chem., Article ASAP (DOI: 10.1021/ac1033177 Publication Date (Web): March 25, 2011).

In 2009, the U.S. Department of Energy's Brookhaven National Laboratory started construction of the National Synchrotron Light Source II (NSLS-II), which is a new advanced synchrotron X-ray source with a 3 GeV storage ring and around 30 beamlines. Construction has now passed the halfway stage, and magnet installation has just started. The completion of the facility is expected in 2015. For further information, visit the web page, http://www.bnl.gov/nsls2/

It is extremely important to develop new X-ray sources for future X-ray spectrometry. One promising direction is a table-top synchrotron X-ray source, which consists of a high-power pulse laser and an undulator. The method uses acceleration of electrons by pulse laser photons. The idea becomes realistic once the energy reaches GeV and other properties such as stability, emittance etc are improved sufficiently. For such development, it is indispensable to establish the method for quantitatively investigating the structure of the electron beam in time and space. Recently, a German group succeeded in taking snapshots of the magnetic field generated by an accelerated electron bunch and simultaneously of a plasma wave by a combination of two techniques: time-resolved polarimetry and plasma shadowgraphy. For more information, see the paper, "Real-time observation of laser-driven electron acceleration", A. Buck et al., Nature Physics (Published online, March 13, 2011 DOI:10.1038/nphys1942).

As a result of the Tohoku Region Pacific Coast Earthquake in Japan, which took place on March 11, 2011, nearly 30,000 people were killed or are still missing. As can be clearly seen from the map of the magnitude of shaking intensity (see, for example, http://www.scientificamerican.com/article.cfm?id=fast-facts-japan), several research facilities were affected by this disaster. Very strong quakes took place in Tsukuba, Ibaraki prefecture, where the Photon Factory, a synchrotron source, is located. However, first of all, the map does not correspond very well to the loss of lives and damage to buildings, roads, railways and other infrastructure. While the coastal areas of Miyagi, Iwate and Fukushima prefectures were destroyed by the tsunami, many cities and towns in the inland area were quite safe. In spite of the largest earthquake since scientific surveys started, damage was minimal. No lives were lost, and no buildings were completely destroyed in the campus of the Photon Factory. The detailed status of the facility is available in the following Web page, http://pfwww.kek.jp/whats_new/earthquakeinfo/announce_e.html.

All beamtime allocated in the term from May to September has been cancelled. On the other hand, another Japanese synchrotron radiation facility, SPring-8 had no damage, because the location is far from the source of the earthquake. The SPring-8 plans to accept some users of the Photon Factory for experiments. For further information, visit the Web page, http://www.spring8.or.jp/en/urgentnews/110401

A research team led by Professor J. Larsson (Lund University, Sweden) has recently performed time-resolved X-ray reflectivity measurements with 100 picosecond resolution at ID09B, at the European Synchrotron Radiation Facility (ESRF). The experiment is a so-called pump-probe measurement, i.e., the repetition of the measurement with systematic change of the delay time of the pump (laser light) and probe (X-ray) pulses. In their research, amorphous carbon films with a thickness of 46 nm were excited with laser pulses (100 fs duration, 800 nm wavelength, and 70 mJ/cm² fluence). Here, the laser-induced stress caused a rapid expansion of the thin film followed by a relaxation of the film thickness as heat diffused into the silicon substrate. The researchers succeeded in measuring changes in film thickness by X-ray reflectivity with a short X-ray pulse (100 ps duration). It was observed that thermal stress generated by laser excitation causes the film to rapidly expand and increases the surface roughness substantially. The subsequent relaxation of film thickness is governed by heat diffusion into the substrate. For more information, see the paper, "Picosecond time-resolved x-ray reflectivity of a laser-heated amorphous carbon film", R. Nuske et al., Appl. Phys. Lett. 98, 101909 (2011).

One of the hottest topics in X-ray crystallography in the early 21^st century is coherent X-ray diffraction imaging and its application to the determination of atomic structures of non-crystalline materials - the ultimate goal can be a single molecule. The technique appears to require non-ordinary coherent photon sources, such as X-ray free-electron lasers (XFEL), which are now in operation at Stanford. On the other hand, there are several challenging questions basically concerning sample damage, Coulomb explosion, and the role of nonlinearity. Recently, Dr. A. Fratalocchi and his colleague published their calculations showing that XFEL-based single-molecule imaging will only be possible with a few-hundred long attosecond pulses, due to significant radiation damage and the formation of preferred multisoliton clusters which reshape the overall electronic density of the molecular system at the femtosecond scale. For more information, see the papers, "Single-Molecule Imaging with X-Ray Free-Electron Lasers: Dream or Reality?", A. Fratalocchi et al., Phys. Rev. Lett. 106, 105504 (2011).

A French-Belgian joint group led by Dr. V. Rouchon (Centre de Recherche sur la Conservation des Collections, MNHN-MCC-CNRS, France) and Professor K. Janssens (Universiteit Antwerpen, Belgium) recently published an interesting paper on the application of X-ray spectrometry to cultural heritage. For many years, in Europe, iron gall inks have been used for writing manuscripts, and they could damage the paper via two major ways: (i) acid hydrolysis, enhanced by humidity, and (ii) oxidative depolymerization provoked by the presence of oxygen and free Fe(II) ions. The present research aimed to give some quantitative evidence for each contribution by studying depolymerization of cellulose under various environmental conditions, with viscometry and related changes in the oxidation state of iron determined by X-ray absorption near-edge spectrometry. It was found that residual amounts of oxygen (less than 0.1%) promote cellulose depolymerization, whereas the level of relative humidity has no impact. For more information, see the paper, "Room-Temperature Study of Iron Gall Ink Impregnated Paper Degradation under Various Oxygen and Humidity Conditions: Time-Dependent Monitoring by Viscosity and X-ray Absorption Near-Edge Spectrometry Measurements", V. Rouchon et al., Anal. Chem., 83, 2589 (2011).