July 2015 Archives

Dr. F. Dorchies (Universite Bordeaux, CNRS-CELIA, France) and his colleagues have recently developed a laser-base X-ray absorption spectrometer covering 0.5-4.0 keV with a time resolution of around 3.3 pico second. The spectrometer uses bremsstrahlung caused by the extremely high impact of laser pulses on the metallic target. To perform time-resolved X-ray spectroscopic studies, there have been quite a few challenges. For most research, it is crucial to avoid damaging/destroying samples, and the measuring time should not be very long. In addition, scientists don't like to compromise the signal-to-background ratio of spectral data taken at each time point, even though the quality is not the same as that of ordinary X-ray absorption spectra. The authors seem to believe that they are getting some breakthroughs. Their setup is a combination of a table-top laser (Ti: Sapphire, 800nm, 150mJ, 10Hz) and a Johan spectrometer equipped with a CCD camera. A set of polycapillary optics were employed as a beamline transport between the X-ray source and the sample (1 m distance) to maintain a clean, independent and flexible environment for the sample. The X-ray intensity near the Al K edge and Cu L edges is 1.3 × 10⁶ photons/eV/pulse. For more information, see the paper, "Experimental station for laser-based picosecond time-resolved x-ray absorption near-edge spectroscopy", F. Dorchies et al., Rev. Sci. Instrum. 86, 073106 (2015).

Since the development of EPMA (electron probe micro analysis) by Castaing's PhD thesis in 1951, great efforts have been made to improve the technique. It was believed that the use of standard samples is absolutely indispensable to the determination of the concentration of each element. This can be a limit for some fields, such as nuclear materials application, where the quantification of minor actinides in fresh or spent fuel is demanded with no availability of any standard samples. In France, Dr. A Moy (Universite de Montpellier) and his colleague have recently reported successful standardless analysis of Pb and U in PbS, PbTe, PbCl₂, Pb₅(VO₄)₃Cl (vanadinite), and UO₂, by measuring absolute Mα and Mβ X-ray intensity by a wavelength dispersive spectrometer. Experimentally obtained X-ray intensity was converted into absolute X-ray yields by evaluating the detector efficiency and then compared with calculated background X-ray intensity based on Monte Carlo simulations. For more information, see the paper, "Standardless quantification of heavy elements by electron probe microanalysis", A. Moy et al., Anal. Chem. 114, 255501 (2015).