teacher notes
2.2 What is a synchrotron?
Overview
This document provides information on what a synchrotron is, how they work, and why Australia has
invested in one.
What is a synchrotron?
An aerial photo of the Australian Synchrotron
Image courtesy: Australian Synchrotron, State of Victoria
A synchrotron is a particle accelerator that produces very bright light (electromagnetic waves) in the
region from infrared through to X-rays. There are currently about 50 synchrotrons in use in the world.
The development of the Australian Synchrotron cost $206.3 million. Given that the Telstra Dome cost
$250 million, and the fact that there are approximately 20 million people in Australia, it is a
comparatively small price per person considering the technological advances this new scientific tool
will facilitate.
The Australian Synchrotron is 216 meters in circumference and is located near Monash University,
Victoria. It became active in mid 2007.
Why are synchrotrons useful?
X-rays produced by a synchrotron are 108 times brighter than the X-rays from a conventional X-ray
machine in a hospital.
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Brightness of the light produced by the Australia Synchrotron
Image courtesy: Australian Synchrotron, State of Victoria
Conventional X-rays can only be used to look at hard tissue (such as bones or teeth). Synchrotron Xray images have a much higher resolution than conventional X-rays which means they have the
advantage of also being able to reveal fine details of soft tissue.
The synchrotron in France provides exceptionally clear angiograms of heart tissue while the Italian
Synchrotron is developing a mammography capability for breast cancer detection. Other applications
include detection of flaws and cracks in composite materials used in aerospace applications.
A conventional X-ray image of a
human finger joint
A synchrotron X-ray image of a
human finger joint
A synchrotron phase contrast Xray image of a human finger joint
Image courtesy: Australian Synchrotron, State of Victoria
The experiments or measurements that can be carried out using a synchrotron fall into four main
categories:
•
Diffraction/scattering for crystallography, including protein crystallography.
•
Spectroscopy for analysis of chemical compositions.
•
Polarimetry for measuring the shape of complex molecules, in particular proteins, and the
properties of magnetic materials.
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•
Imaging from highly detailed imaging of small animals, and ultimately humans, down to the
substructure of biological and physical material, using light from infrared through to hard X-rays.
Why invest in a $206 million synchrotron for Australian researchers?
When Wilhelm Roentgen discovered X-rays in 1895, the benefits to mankind were not immediately
apparent. At the time people could not begin to imagine the benefits that would become apparent as a
result of the discovery.
Wilhelm Roentgen
Image courtesy: AIP Emilio Segrè Visual Archives
When Michael Faraday discovered how to generate electricity by moving a magnet near a coil of wire
he was asked “What use could it possibly have?” to which he responded, “What use is a new born
baby?”
The same philosophy can be applied to the discoveries made with the very powerful light from a
synchrotron. Their potential use is currently unknown.
In addition to having a high intensity, the synchrotron light has other properties useful to researchers:
•
It is produced in the range of wavelengths ( ) from 10-11 m (hard X-rays) to10-6 m (infrared light).
•
It is emitted in short pulses (~100 ps wide spaced at 2 ns).
•
It arrives in parallel rays (collimated).
•
It is partially coherent.
•
It is highly polarised (limited to a single plane for direction of wave vibration), and can, for some
types of undulators, be circularly or elliptically polarised.
•
Specific wavelengths can be isolated using diffraction gratings or crystal gratings. These are
monochromators and are useful for examining objects whose structural dimensions are similar to
the single wavelength, or for exciting states at well defined energies.
•
Light is released as a very narrow cone from the undulators and this is then focussed to provide a
very narrow beam at the work station. Bending magnets are now rarely used for light sources.
The diverse uses of synchrotrons
Synchrotrons have a diverse range of uses. Some of the areas that synchrotrons are useful in are;
•
•
•
•
•
•
•
medical imaging and therapy,
materials engineering,
environment,
forensics,
manufacturing,
medicine and pharmaceuticals,
agriculture,
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•
•
minerals,
micromachining.
Materials Engineering
The Australian Defence Force has used synchrotron light
to assist in the development of improved ceramic coatings
for jet engines. These coatings allow for greater thrust by
protecting the engines.
Image courtesy: Australian Synchrotron, State of Victoria
Environment
Synchrotrons are being used to investigate
the sources of pollutants in water supplies.
This has resulted in cleaner drinking water in
developing countries.
Air samples collected in New York after the
collapse of the World Trade Centre were
analysed at a United States synchrotron. The
results showed how the debris pile acted like
a chemical factory and emitted toxic metals,
acids and organics, all with potential health
impacts.
Image courtesy: Australian Synchrotron, State of Victoria
Forensics
Extremely small samples from crime scenes can be analysed using synchrotron technology. Forged
documents and counterfeit money can be detected using synchrotron techniques.
Manufacturing
Cadbury UK wanted to produce the most stable, smooth and best-tasting chocolate. They utilised the
synchrotron to investigate the manufacturing process at the molecular level to optimise the production
conditions.
Medicine and pharmaceuticals
By modelling virus proteins, medicines can be created to
block these proteins. Relenza which blocks flu virus lifecycles was created by CSIRO scientists using a
synchrotron.
Image courtesy: Australian Synchrotron, State of Victoria
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Agriculture
Scientists created Optim, a commercial fibre made from wool that mimics the structure of silk. The
synchrotron was used to confirm its structure in comparison to silk.
Minerals
Using synchrotron light, scientists have studied nickel and cobalt during extraction. Using these studies
production conditions have been optimised. This has resulted in extraction rates increasing from 60%
up to 95%.
Micromachining
Synchrotron light is used to manufacture tiny machine parts. Inkjet printer heads are an everyday
example of this micromachining.
Image courtesy: Australian Synchrotron, State of Victoria
2003 Nobel Prize for chemistry
Biochemists Peter Agre and Roderick MacKinnon used a United
States synchrotron as part of their research which led to winning
2003 Nobel Prize for Chemistry. They studied how water flows
across cellular membranes and how cells communicate. The
work will help understand the molecular pathways of disease.
Image courtesy: Australian Synchrotron, State of Victoria
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Synchrotron Facts
•
Whenever a charged particle accelerates it emits electromagnetic waves. An excellent animation of
accelerated charged particles in a synchrotron emitting electromagnet waves can be found at
www.isa.au.dk/animations/Finalmovie/astrid_ total_ v2.mov
•
The power in the waves is proportional to the square of the acceleration of the particle.
•
The electrons in a synchrotron have a speed that approaches 99.9997% of the speed of light.
•
The large speed implies a large centripetal acceleration, a =
v2
and therefore large quantities of
r
electromagnetic waves are produced.
•
The electromagnetic radiation released by charged particles in accelerators was originally regarded
as a nuisance, however it was realised that the electromagnetic waves could be put to good use.
•
Oscillatory electric fields are used to accelerate the electrons.
•
Magnetic fields cannot change the speed of the electron; they can only change the direction of the
velocity. Magnetic fields are used in bending magnets to make the electrons move in curved paths,
and in wigglers and undulators to cause sinusoidal oscillations of the electrons along their primarily
linear trajectories.
A diagrammatic representation of the beamlines within the Australian Synchrotron
Image courtesy: Australian Synchrotron, State of Victoria
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The electromagnetic waves (such as high energy X-rays) emitted from a fast particle travelling in a
circular path are emitted in the forward direction along the direction of motion of the particle. The
beam of electromagnetic waves produced sweeps around like a train’s headlight as the particle travels
along the curved path.
A diagrammatic representation of a bending magnet
Image courtesy: Australian Synchrotron, State of Victoria
Bending magnets, like the one shown left, cause the
electrons to move in a curved path.
The intensity of the electromagnetic waves produced is increased by inserting magnets in arrangements
that are called ‘wigglers’ and ‘undulators’. Both serve to cause the electron to undergo rapid oscillatory
motion superimposed on its primarily linear path. This rapid acceleration causes the electron to release
intense electromagnetic radiation in the direction of travel. The acceleration is largest at the extreme of
the oscillations, ie at the turning points of the sinusoidal oscillatory motion.
A diagrammatic representation of a wiggler
Image courtesy: Australian Synchrotron, State of Victoria
Wigglers (above) are designed to produce more intense electromagnet waves than bending magnets.
The electrons take a sinusoidal path through a wiggler and a cone of light is emitted at each turning
point in the sinusoidal trajectory. The final intensity increases with the number of oscillations in the
magnetic field. The beam appears as a broad beam of incoherent (random phase) radiation in the
direction of the straight section of the storage ring containing the wiggler.
A diagrammatic representation of an undulator
Image courtesy: Australian Synchrotron, State of Victoria
Undulators (above) use less powerful magnets to produce gentler undulations in the electron beam.
Careful matching of the transverse motion to the transit speed of the electrons through the device can
cause the amplitudes of the cones of light emitted in this manner to interfere constructively. The
optimal wavelengths can be changed by altering the gap between the component magnets, so that the
synchrotron light is tuneable to specific wavelength bands. The beam produced by an undulator is
narrow and coherent.
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Technical data for the Australian Synchrotron
Energy:
Circumference:
Number of straights:
Length of straights:
Current:
Bending magnet field:
Electron speed:
3.0 GeV
216 m
12
5.397 m
200 mA
1.300 T
99.9997% of the speed of light
‘First Light’ (the sustained generation of synchrotron light in the Australian Synchrotron facility) was
observed early on the morning of 14 July, 2006, when a 1 mA current was stored for a period of
several minutes and X-rays were detected by the X-ray Diagnostic Beamline.
Why are modern synchrotrons so large?
For the sections in a synchrotron that curve the path of the electrons, the key physical principle is that
the magnetic force provides the centripetal force:
Fcentripetal = Fmagnetic
mv 2
= qvB
r
r=
mv
qB
Producing maximum radiation requires a large speed and hence large centripetal acceleration. Early
particle accelerators had a small radius.
Ernest Lawrence holding a ‘cyclotron’ (circa 1931) with a diameter of 12.7 cm
Image courtesy: Ernest Lawrence Berkeley National Laboratory, courtesy AIP Emilio Segrè Visual Archives
Ernest Lawrence, shown above, is holding one of the first particle accelerators (the cyclotron), that was
only 12.7 cm in diameter. Lawrence not only used his knowledge of cyclotrons for chemistry and
physics but also for biomedicine. He believed in the promised of particle accelerators as a possible
weapon against cancer. In 1937, Lawrence bought his mother (who had been diagnosed with
inoperable cancer) to San Francisco for treatment with a colleague’s X-ray tube which used high
energy charged particles from an accelerator. After this treatment her condition improved dramatically.
For further information on this visit http://www.aip.org/history/lawrence/radlab.htm
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Synchrotron light (located within the circle)
Image courtesy: Advanced Light Source
Synchrotron radiation was discovered in 1947 coming from a particle accelerator called a synchocyclotron (later shortened to synchrotron).
For a personal account of the discovery see: http://en.wikipedia.org/wiki/Synchrotron_radiation
Modern day particle accelerators have a much larger radius to create larger electron speeds, such as the
synchrotron in France which has a radius of almost two kilometres.
European Synchrotron, Grenoble, France –
one of world’s largest at ~2km circumference
Image courtesy: European Synchrotron Radiation Facility
The electrons in a synchrotron cannot travel faster than the speed of light. Why?
The electrons in a synchrotron travel at 99.9997% of the speed of light. Einstein’s expression for the
relativistic increase in mass with velocity needs to be considered:
m=
mo
2
1 v2
c
where
m = mass (kg)
mo = rest mass (kg)
v = speed (m s-1)
c = speed of light (300,000,000 m s-1)
We see that as the velocity approaches the speed of light, the denominator in the above equation
approaches zero, thus the mass tends towards infinity.
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Albert Einstein
Image courtesy: The Albert Einstein Archives, The Hebrew University of Jerusalem, Israel
Facts on how the synchrotron light is used
The Australian Synchrotron opened in mid 2007 and will be used by more than 1200 Australian
scientists. Many experiments can be run at the same time, some taking several days. Initially there will
be nine beam lines, with a capacity for more than 30 individual beamlines in the future.
The light source will enable crop research, drug design, forensic analysis, new material development,
food technology research and advanced manufacturing.
Time on beamlines will be purchased by industry and available ‘free of charge’ to university
researchers.
The very intense hard X-rays (small wavelength) will be useful in diffraction experiments to determine
structural features of a diverse range of materials and complex molecules (ie proteins).
Protein crystal - Using tiny
protein crystals, biologists from
the Max Planck working group
are able to investigate the
protein's exact structure
Image courtesy: HASYLAB and Max
Planck working groups, Hamburg
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X-ray diffraction is a key technique that is used by many researches to determine the structure of
complex molecules and materials.
How water flows through a cell membrane
Image courtesy: Australian Synchrotron, State of Victoria
Biochemists Peter Agre and Roderick MacKinnon used a United States synchrotron as part of their
research leading to their 2003 Nobel Prize for Chemistry on how water flows across cellular
membranes and how cells communicate. The work will help understand the molecular pathways of
disease.
Biophysicist Dr Tim St Pierre at the University of Western Australia (UWA) uses X-ray diffraction
techniques with X-rays from a synchrotron to analyse the amount of iron deposited in living tissue
affected by ‘iron-overload’ disease.
Physicist Dr Peter Hammond at UWA uses ultra-violet light from a synchrotron to study how long, on
average, atoms stay in an excited state – this is called the lifetime of the state. To do this special
techniques have to be developed so that signals from experiments can be recorded on very short
timescales. Each light pulse from the synchrotron is about 100 picoseconds long and the pulses are
spaced 2 nanoseconds apart. The diagram below shows the number of electrons counted (one by one!)
in a detector as a function of time with respect to a light pulse from the synchrotron and includes
electrons arising from a subsequent light pulse. Each electron is released from an atom when the atom
absorbs a photon of light which ionizes the atom.
Note the time scale: 1 picosecond = 1 ps = 10-12 s
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Electron Yield
0
500
1000
1500
Picoseconds
2000
The number of electrons counted in a detector as a function of time with respect to a light pulse from
the synchrotron. The experiment was performed at Sincrotrone Trieste in Italy in January 2007.
Image courtesy: Peter Hammond
Investigating atomic states: The infrared, visible and UV light produced by a synchrotron can be used
to probe the outer shell (low energy) processes in atoms and molecules. The X-rays produced by a
synchrotron can be used to probe the inner shell (high energy) process in atoms and molecules.
Further reading and resources
•
An excellent animation showing the production of X-rays in a synchrotron can be viewed at
www.isa.au.dk/animations/Finalmovie/astrid_ total_ v2.mov
•
The Australian Synchrotron website has more material www.synchrotron.vic.gov.au
•
The Canadian Synchrotron website contains resources www.lightsource.ca
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