Synchrotrons – making the light fantasticThe Victorian Government is building a $206 million synchrotron in Melbourne. Why invest so much money in a machine that most people have never heard of?
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Back to basics You will get more from this topic if you have mastered the basics of atoms and molecules and electromagnetic radiation – these links will take you to an annotated list of sites with helpful background information. Key text
The nature of synchrotron radiation Synchrotron radiation – also referred to as synchrotron light – is a type of electromagnetic radiation – energy that travels in the form of electromagnetic waves.
What’s more, the intensity of light being produced is staggering – a million times brighter than sunlight and a billion times greater than the radiation from a typical laboratory X-ray source. This makes synchrotron radiation possibly the most powerful light produced by humans. The emerging beams are extremely fine – just a few thousandths of a millimetre across – and are emitted in extremely short pulses, typically 10-100 picoseconds in length (a picosecond is a trillionth of a second). Uses of synchrotron radiation The uses of synchrotron X-rays are many and range from designing drugs to making micromachines. Let’s explore some of these applications.
Currently the most important use of synchrotron X-rays is X-ray crystallography, a technique first developed by William and Lawrence Bragg. With this technique, X-rays are fired through crystals and the resulting patterns reveal the atomic content and molecular structure of the crystal – often a protein. Studies using synchrotron X-rays for protein crystallography can help scientists understand and imitate complex structures – from cellulose fibre to spiders' silk.
Analysing viral proteins
Investigating cell structure
Lithography for computer chips
Materials science The powerful penetrating characteristics of synchrotron light also allow researchers to probe below the surface of electronic devices or to check the integrity of metal joining processes such as welding.
The first particle accelerators were built in the 1930s by physicists who were interested in finding out about the elementary particles that make up atoms. These machines – atom smashers – accelerated particles to tremendous speeds then collided them into an atom, thus breaking the atom into its component parts. In some accelerators the particles were propelled around a circular track, and when the particles were forced to move around the circle, they lost energy by emitting a beam of synchrotron radiation. This beam made the experiments of the particle physicists difficult to perform (Box 1: The first particle accelerators and synchrotrons). But researchers soon realised that synchrotron radiation was a valuable research tool, and began to use these machines as a source of radiation. They became known as first-generation synchrotrons. Second-generation synchrotrons were built solely for their ability to generate synchrotron radiation. They were basically circular rings with ports arranged around the outside through which the intense synchrotron radiation passed. In the last two decades, synchrotron technology has reached new heights. Magnetic devices are now installed within the ring, causing the stream of speeding electrons to oscillate as it passes by. This greatly increases the intensity of the beam. This type of facility is known as a third-generation synchrotron. Using synchrotron radiation
The Australian synchrotron, which is a third-generation machine, will initially have nine beamlines but will have the capacity to increase to 35 beamlines in the future, making it possible for 35 completely different experiments to be conducted at the same time. The Australian synchrotron is due to open in 2007 with the first nine beamlines. Is it worth the cost? There are few areas of modern research and development where synchrotron light doesn’t have some potential role to play. But is it worth several hundred million dollars of investment? Most Australian research institutions believe it is. A national facility means we won’t have to rely on limited access to overseas facilities. We’ll have a greater capacity to develop our own projects and provide local industry with dedicated, cutting-edge synchrotron support. And we’ll give our own top scientists a better reason for staying in Australia, while attracting top researchers from overseas.
Particle physics In the 1930s, scientists observed that when cosmic rays (highly energetic protons) from outer space hit atoms of lead, many smaller particles were sprayed out – particles that were much smaller than neutrons, protons and electrons. These were the elementary particles from which all matter is ultimately constructed. The hunt was on to find out what they were and how they worked. To study them in a controllable way, scientists needed to collide highly energetic particles with atoms. To do this, they built machines called particle accelerators, sometimes referred to as atom smashers. In these devices, particles – usually electrons – are accelerated to tremendous speeds using electromagnetic force, and then slammed into target atoms. The resulting collision produces a shower of tiny particles and radiation. By analysing the results of these collisions, particle physicists are able to build models of what these elementary particles are and how they interact. The greater they can accelerate the initial speeding electron, the more violent the collision, and the more they can learn about the elementary particles that get thrown out. The size of accelerators increased The first particle accelerators were small affairs that could comfortably sit on the lab bench. However, as the technology for accelerating electrons progressed, the size of the machines grew. They quickly became great metal monsters consisting of vast arrays of magnets, conductors and sensors strung together in ever increasing complexity. And because the speeding electron has to travel in a vacuum – if it travels through air it will interact with the atoms in the surrounding gas – keeping a long tube evacuated of air for long periods takes a lot of machinery, further adding to the size of the apparatus. Circular accelerators In the early 1960s a new type of accelerator proved to be quite popular with researchers. These circular accelerators send electrons whizzing around in a giant vacuum tube in the shape of an enormous circular ring, which is usually over 50 metres in diameter. The electrons are held in this circular path by powerful magnets. Once or twice in each orbit the electrons are hit with synchronised pulses of microwaves to accelerate them. In a cyclotron, as the electrons approach the speed of light they are released from their circular orbit and allowed to fly off at a tangent to strike a target. In a synchrotron, the electrons continue to orbit within the ring, passing through magnetic fields and releasing beams of synchrotron radiation. Accelerating the electrons To understand how the electrons are accelerated, think of the biblical story of David and Goliath. David killed Goliath with a stone thrown from his sling. The sling was a leather strap with a stone at one end. David whirled the sling around his head, accelerating the stone to an enormous speed. He then released the stone with precision timing. It flew off at a tangent from its circular path striking Goliath in the head, killing him instantly. The stone is like the electrons in the cyclotron. The sling is like the magnets that hold the electrons on a circular path. When David synchronised his movements with the cycle of the stone, each orbit of the sling caused the stone to move faster and faster. So synchrotrons are like enormous slings that swing electrons around in a circular path giving them more and more energy with each orbit. But there’s a major limitation with this process. When electrons (or any charged particles) are accelerated to keep them in a circular path they will emit electromagnetic radiation in a narrow beam in front of them (which is at a tangent to the circular path along which they’re moving). What’s more, the more energy you try to put into the electrons, the more electromagnetic radiation they emit. This proved to be a real nuisance for particle physicists because it meant that they could only accelerate an electron to a certain level inside a synchrotron. Beyond this point it didn’t matter how much energy they pumped into the electron, it was simply emitted as intense electromagnetic radiation. So, it seemed, synchrotrons may have had their day because they could only achieve so much in particle physics. Using the radiation from synchrotrons But then scientists started wondering if the electromagnetic radiation being emitted by the accelerating electrons might actually serve some useful purpose. This radiation was known as synchrotron radiation – or synchrotron light – and it was quickly realised that the intensity of the radiation and the fact that it could be precisely controlled made it extremely valuable. And so it was that through the 1960s and 70s, the synchrotrons that had been built to study sub-atomic particle physics began to be used for the synchrotron radiation that was produced as a by-product. These are known as first-generation synchrotrons. Related sites
Australasian Science July 2008, page 48 The synchrotron environment Provides information on environmental applications of synchrotrons.
April 2008, page 48 Soft X-rays: The Swiss Army knife of synchrotron light Discusses the new soft X-ray beamline at the Australian synchrotron.
September 2007, pages 16-18 Synchrotron scientists unpack their suitcases (by Stephen Luntz) Provides information on the new synchrotron facilities in Melbourne.
May 2007, page 26-28 Brightest Aussie light set to probe matter (by Peter Pockley) Explains the remarkable capacity of the synchrotron to unravel the innermost structure of stuff.
August 2006, page 13 Sychrotron spins for the first time Reports that a full circle of synchrotron light has been achieved for the first time.
July 2002, pages 25-28 What is a synchrotron and why does Australia need one? (by Keith Nugent) Explains how a synchrotron produces X-rays and how researchers can use them.
The Helix August-September 2005, pages 14-17 Synchronicity – Australia's first synchrotron (by Philippa Rowlands) Describes the features of a synchrotron, the types of light produced and the uses of synchrotron light.
New Scientist 27 July 2002, page 18 Extreme laser sheds light on nanoworld (by Jeff Hecht) Explains that features of nanostructures are now measured by light from synchrotrons, and that new laser technology may be able to do the same thing.
4 May 2002, page 8 Going straight (by Eugenie Samuel) Particle physicists are proposing a new linear accelerator, in which beams of electrons and positrons would collide at extremely high energies.
RTD Info February 2007 Life through the eye of the synchrotron Looks at the use of synchrotron radiation as a tool by biologists.
Welcome to the Australian synchrotron (Australian Synchrotron)
Gives background information on synchrotrons, synchrotron radiation, case studies of synchrotron research and up-to-date coverage of the Australian synchrotron.
Canadian light source virtual tour (Canadian Light Source Inc., Canada)
A virtual tour of the Canadian synchrotron and explanation of points of interest.
The Advanced Light Source – A tool for solving the mysteries of materials (Lawrence Berkeley National Laboratory, USA)
Describes one particular synchrotron – the ALS. Explains how synchrotron light is produced and what it is used for.
Australian Broadcasting Corporation (transcripts)
Australian Academy of Technological Sciences and Engineering The following papers describe specific applications of synchrotron radiation:
atom. The fundamental unit of all matter, consisting of a nucleus of protons and neutrons surrounded by orbiting electrons (or in the case of hydrogen, just one electron). For more information see Back to Basics: Atoms and molecules (Australian Academy of Science). electromagnetic force. One of the four forces – gravity, strong force, electromagnetic force, weak force – that act on particles. Electromagnetic force acts on charged particles and is made up of electric and magnetic forces (eg, moving magnets produce electric forces and moving electric charges produce magnetic forces). The electric charge that is the source of electromagnetic force can either be positive or negative. Because there are two types of charge, the electromagnetic force can be either attractive or repulsive. Opposite charges attract, like charges repel. Physics theory explains that electromagnetic force is carried by photons (packets of electromagnetic radiation). For more information see Electromagnetic force (Argonne National Laboratory, USA). electromagnetic radiation. Electromagnetic radiation is simply energy which travels through space at about 300,000 kilometres per second – the speed of light. We imagine radiation moving like a wave. The distance between two adjacent wave crests is called a wavelength. The shorter the wavelength, the more energetic the radiation is said to be. Also, the shorter the wavelength, the greater the frequency of the radiation. Other than wavelength, frequency and energy there is no difference between a radio wave, an X-ray and the colour green. They all possess the same physical nature. For more information see Back to Basics: Electromagnetic radiation (Australian Academy of Science) and Electromagnetic Spectrum (NASA Goddard Space Flight Center, USA). electron. A negatively charged particle that is a constituent of an atom. Electrons can move from atom to atom. When they do, they produce an electric current. elementary particle. A particle that cannot be subdivided into component parts. These particles are also referred to as fundamental particles. For more information see Theory – fundamental particles (Stanford Linear Accelerator Center, USA). infrared light. A form of electromagnetic radiation with wavelengths between 0. 7 micrometres (0.0007 millimetres) and 1 millimetre. These wavelengths are longer than those of visible light, but shorter than those of microwaves. (The prefix 'infra' means 'below; infrared refers to radiation below the frequency of red light.) Infrared light is primarily thermal radiation, and we can think of this as being heat. microwaves. The highest frequency radio waves, with wavelengths between about 1 millimetre and 30 centimetres and frequencies between about 300 gigahertz and 300 megahertz. Microwaves are a type of electromagnetic radiation. neutron. A particle having no charge that is a constituent of an atom. It has a mass similar to a proton. protein. A large molecule composed of a linear sequence of amino acids. This linear sequence is a protein's primary structure. Short sequences within the protein molecule can interact to form regular folds (eg, alpha helix and beta pleated sheet) called the secondary structure. Further folding from interaction between sites in the secondary structure forms the tertiary structure of the protein. Proteins are essential to the structure and function of cells. They account for more than 50 per cent of the dry weight of most cells, and are involved in most cell processes. Examples of proteins include enzymes, collagen in tendons and ligaments and some hormones. More information can be found at Protein structure and diversity (Molecular Biology Notebook, Rothamsted Research, UK). protons and neutrons. Small particles that form the nucleus of an atom. Protons have a small positive charge; neutrons have no charge. X-ray. A high energy form of electromagnetic radiation with very short wavelengths (less than 1 x
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