Precision tests of QED
A summary of recent tests of the theory of Quantum Electrodynamics
in medium-Z ions. Accelerators, Tokamaks, Electron Beam Ion Traps and other devices are used
in these studies.
Theoretical computation
of Atomic Form Factors
How can relativistic quantum mechanics predict absorption and scattering coefficients, and are the results accurate?
Atomic form factors determine photoelectric cross-sections, elastic and inelastic
scattering cross-sections and X-ray (Bragg-Laue) coherent diffraction profiles.
Our Web database has been receiving 10000-20000 hits per month for over five years since
it’s electronic installation as one of the three major references for
atomic form factors and attenuation coefficients. Reliable knowledge of these
factors is required for conventional fields such as crystallography and radiography,
and also for the new fields of X-ray Anomalous Fine Structure (XAFS) and
Multiple-wavelength Anomalous Dispersion (MAD).
Experimental measurement
of the atomic form factors, attenuation and scattering in matter
Looks at the importance of careful attenuation measurement in differentiating
between different theories. Our recent experiments are two orders of magnitude more accurate than earlier work
and reveal new physics, new processes and new applications. Major questions remain.
Novel High-energy Sources for
QED tests
A problem in most X-ray QED measurements is the presence of
satellite contamination and Doppler shifts and broadening from fast
beam sources. Recently, sources known as Electron Beam Ion Traps
(pictured) have been shown to avoid much of these problems, and still
allow desired charge states to be produced and measured.
Synchrotron
Beamline Developments and XAFS
Diagnostics used to measure flux and energy in synchrotrons are in
a state of development.
XAFS and Solid State Physics: Theory and Experiment
Some third or more of Australian synchrotron research uses XAFS (and the related technique called XANES) to indentify band distances,
chemical valence, nearest neighbour coordination and geometry, and local structure.
Powder Diffraction and X-ray Crystallography
Powder Diffraction is often required for structural determination of biologically active molecules, viruses,
proteins or enzymes as well as for small inorganic molecules, especially where the samples cannot be grown into large crystals.
Applications
These issues impact upon X-ray diffraction theory and the interaction
of X-rays with photographic emulsions. Applications of these ideas have led to new calibration devices for
radiography and mammography, now patented in the US as part of the Quantum Metrology Group effort in the
Atomic Physics Division at the National Institute for Standards and Technology, USA.
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