Some of the theoretical developments in the computation of form factors have resulted in significant deviations from earlier work, which can be tested by suitable experiments. Here the atomic scattering factor is given for Uranium at medium X-ray energies (keV). Click the figure for the corresponding attenuation coefficients.

Welcome to X-ray Optics

X-ray optics is concerned with the interaction of photons with matter. High energy (X-ray) photons are of direct interest, because this often reflects the dominant atomic structure and atomic physics. However VUV photons and gamma-rays are also subjects of investigation.

Quantum Electrodynamics is one of the two best-tested theories in physics and science, and lies at the heart of atomic physics. Yet certain problems in its formulation lead people like Roger Penrose to assume that there are fundamental flaws in the theory which may be revealed by an appropriate experiment. The type of experiment pursued here may reveal such an inadequacy, by being more sensitive to important terms and interactions than other available tests. QED is the primary explanation of the interaction of light and charge, and is fundamental to much of the physics which we assume and rely on in the world today.

The beauty of (X-ray) optics and atomic physics is that they are among the most accessible to simultaneous theoretical and experimental investigations. This means that honours-level projects in this field can be predominantly theoretical or experimental, without losing sight of the direct link to the other. Doctorates involve linking those two threads together into a coherent whole.

What do we do in X-ray Optics?

Our group at the University of Melbourne is exploring the interaction of light with matter, on an experimental and theoretical basis. Particular interest relates to Precision tests of QED; Understanding atomic form factors and near-edge structure; X-ray interactions with detectors including photographic emulsions, ion chambers, backgammon detectors and crystals; Dynamical diffraction; Mammography; The Lobster-eye telescope; Phase Retrieval and the development of X-ray phase imaging; X-ray focussing using Capillary Optics; Absolute Intensities in X-ray Diffraction; and Coherence issues at high-brightness sources.

A few international experiments include Atomic Form Factor measurements at SRICAT, APS beamline 1BM, Chicago, 4th ­17th February 1999; Synchrotron coherence measurement at SRICAT, APS beamline 2ID, Chicago, 20th ­28th August 1999; Atomic Form Factor measurements at ANBF, Tsukuba, 30th November ­ 5th December, 1999; others are in progress.

APS and ANBF were major successes, yielding major publications. A Ph.D. thesis on QED investigations has been completed and has lead to the first precision absolute QED measurement on an EBIT, and the first precision QED measurement of hydrogenic vanadium. The systematics in EBIT measurements of QED and the statistical quality of possible experiments has been dramatically improved by our techniques. The coherence measurements showed significant coherence in the synchrotron beam in a very clean manner, and serves as the prototype for subsequent experiments.

New Measurements: The form factor experiments at Tsukuba and APS followed on from the major success of the form factor theory of Chris. Chantler and the pilot experiment in 1998 at Tsukuba, and observed failures of earlier experimental results reported in the literature. Our new measurements are two orders of magnitude more accurate than earlier experiments, which will 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 limits on the absolute calibration are 0.3%.

New Theory: There has been a lively international debate and discussion of form factors and approaches throughout the year, resulting in several publications. The major new theoretical publication [400 pp] was accepted in 1999, and a major development of this has been published on the web in 2003. This has highlighted inadequacies of other experimental and theoretical approaches. Further theoretical developments by the author have shown great promise in particularly difficult theoretical regimes.

Who's here?

Areas of interest in x-ray optics at the University of Melbourne

Precision tests of QED

Theoretical computation of Atomic Form Factors

Experimental measurement of the atomic form factors, attenuation and scattering in matter

Novel High-energy Sources for QED tests

Synchrotron Beamline Developments / Studies

Interaction of X-rays with photographic emulsions

Improved densitometry/characterisation of X-ray emulsions

Multi-channel X-ray Optics and The Lobster-eye Satellite

For references and publications, see the home pages (e.g. Chantler).

Facilities available

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