What is Synchrotron Radiation?

When charged particles, in particular electrons or positrons, are forced to move in a circular orbit, photons are emitted. At relativistic velocities (when the particles are moving at close to the speed of light) these photons are emitted in a narrow cone in the forward direction, at a tangent to the orbit. In a high energy electron or positron storage ring these photons are emitted with energies ranging from infra-red to energetic (short wavelength) X-rays. This radiation is called Synchrotron Radiation.

Characteristics of Synchrotron Radiation

Synchrotron radiation has a number of unique properties:

• High brightness: synchrotron radiation is extremely intense (hundreds of thousands of times higher than conventional X-ray tubes) and highly collimated.
• Wide energy spectrum: synchrotron radiation is emitted with a wide range of energies, allowing a beam of any energy to be produced.
• Synchrotron radiation is highly polarised.
• It is emitted in very short pulses, typically less that a nano-second (a billionth of a second)

History of X-ray Sources

 
(Click on image for larger jpg)

Since their discovery by Roentgen just over 100 years ago, X-rays have been a powerful tool in research, industry and medicine. All facets of X-ray research have been revolutionised by the use of synchrotron radiation and the high brightness beams now available. The graph shows the rapid increase in the brightness of X-ray beams available for research, since the introduction of synchrotron radiation in the 1960's.

First generation synchrotron sources were high energy physics accelerators, where the synchrotron radiation was an unwanted by-product.

In the 1960s, physicists and chemists began to use the radiation from several of these accelerators in a "parasitic mode". The second generation of synchrotron radiation facilities, such as the Photon Factory in Japan, were constructed expressly to provide synchrotron X-rays for research.

Recently a third generation of facilities is being completed, for example, the 7 GeV Advanced Photon Source in the USA, and are providing even higher brightness X-ray beams, about 10,000 times higher than those of the second generation.

Applications of Synchrotron Radiation

Synchrotron radiation has become an indispensable tool in a wide range of research fields.

Using the intense UV, soft X-ray and hard X-ray beams produced at synchrotron radiation facilities, scientists can: determine the structure of materials and molecules, the electronic (chemical) structure of surfaces and interfaces; analyse tiny trace element concentrations in micron-sized regions; measure local molecular structures in disordered systems eg solutions and catalysts; obtain 3-D CAT scan images with micron resolution, and so on.

One of the first techniques to make use of synchrotron radiation was X-ray crystallography: the determination of atomic structure from X-ray diffraction data.

X-ray crystallography has historically been the primary tool used to investigate the structure of matter: the atomic and crystal structures of most materials have been determined using these techniques.

This structural knowledge is central to the development of many new technologies, e.g. pharmaceuticals and nanotechnology.

Synchrotron radiation, because of the characteristics mentioned above, has not only allowed the extension of conventional crystallographic techniques to the investigation of new materials and macro-molecules, but it has also facilitated major advances in the understanding of the structure and dynamics of ceramics, superconductors, polymers and the structure of surfaces and interfaces, even at the level of single layers of molecules.

Australia possesses outstanding communities of crystallographers and other users of hard and soft X-rays, whose international reputation is very high. Of these, about 120 scientists are currently active users of synchrotron radiation. Key disciplines include protein crystallography, materials characterisation and geoscience using X-ray diffraction, the study of minerals, inorganic chemistry, physics and surface science.

With the high brightness X-ray beams produced by the new third generation synchrotron radiation facilities, a number of totally new capabilities will become possible, further expanding the number of disciplines and research communities making use of synchrotron radiation.

Examples are:

• The high brightness and intensity will make time-resolved crystallography and spectroscopy feasible on a nano-second timescale, e.g. for the study of the dynamics of chemical reactions, which will extend the utilisation of synchrotron radiation by the chemistry, physics and biostructure communities
• The high X-ray energies which will be available at high intensity for the first time will benefit the geoscience community as the higher penetration of the radiation is well suited to high pressure diffraction experiments
• The high brightness of the third generation source is ideally suited to microbeam and imaging applications, including X-ray microscopy, fluorescence micro-analysis and micro-diffraction. For example, the fluorescence X-ray microprobes planned will have detection limits several orders of magnitude lower than current techniques (a few parts per billion for most elements) and a resolution of better than 0.1 microns. These microbeam techniques will be utilised by the environmental science, geophysics and medical physics communities
• Soft X-ray microscopy offers a resolution of about 100 Angstroms and the ability to image wet biological samples. This is finding important applications in biology.

Document details: Original Web document. Author and contact Dr R Garrett

This page was last updated on 4 February, 2004