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What we do at X-Ray Optics

 

 

What do we do in X-Ray and Synchrotron Optics, Atomic and Condensed Matter Science?

We probe fundamental and applied questions about the interaction of light with matter, on an experimental and theoretical basis. How well does relativistic quantum mechanics explain the photoelectric effect in real atoms? How well does it explain solid state near edge structure from synchrotron experiments?

Particular interest relates to

  • Precision tests of QED;
  • Understanding atomic form factors and near-edge structure as seen in XAFS and XANES; Synchrotron development and applications;
  • X-ray detector technology and understanding including backgammon detectors, crystals, photographic emulsions and ion chambers;
  • Powder Diffraction lattice standards;
  • Dynamical diffraction;
  • Mammography;
  • Absolute Intensities in X-ray Diffraction.

A few recent international experiments include precision EBIT tests of QED in hydrogenic and helium-like Vanadium and Titanium. The systematics in EBIT measurements of QED and the statistical quality of possible experiments has been dramatically improved by our techniques.

Other experiments include Atomic Form Factor and XAFS measurements at SRICAT, APS beamline 1BM, Chicago and BESSRC-CAT, APS, beamlines 12BM and 11ID; Synchrotron coherence measurements at SRICAT, APS beamline 2ID, Chicago; a Program Grant on compound XAFS and scattering at ANBF, Tsukuba (now closed); a novel implementation for Stanford SSRL and others. Coherence measurements showed significant coherence in the synchrotron beam in a very clean manner, and serve as a prototype for subsequent experiments.

New Synchrotron Measurements: The form factor experiments at Tsukuba and APS followed major success of the form factor theory of Chantler, addressing observed failures of earlier experimental results reported in the literature. Our new measurements are two orders of magnitude more accurate than earlier experiments, which allow crucial insight and development of theoretical issues. The self-consistency of the data has plunged to around a precision of 0.02%, with the limitation in the final result due to absolute calibration. Current accuracies of the final results are 0.02% to 0.3%, depending upon sample and energy range.

Recent work has developed a Hybrid technique for dilute disordered solutions at room or cryogenic temperatures for transmission and fluorescence. Point accuracies in transmission for 15 mM systems and a simple bending magnet beamline have plunged to 0.01-0.02 % and net accuracies on the active species reach 0.1-0.5%. Expected developments will allow this to attain accuracies of order 0.1% on 1 mM systems.

These accurate data sets permit the measurement of low energy electron inelastic mean free paths and have surprised past conventional theory.

New Theory: There has been a lively international debate and discussion of form factors and approaches throughout the years, resulting in several publications. Major new theoretical publications represent the primary NIST reference standard in the field. Meanwhile the group continues to pursue additional key theoretical developments especially in the near-edge region of XAFS and XANES, with great promise of developing new tools and technology for popular techniques at synchrotrons worldwide.

 

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