Materials Technology

Inside the 40m tower that houses the particle accelerator( during a cleaning and maintenance operation). The accelerator (the centrol column of metal) rises over 20 metres and can generate 15 million volts.

Materials technology
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November 2002

The Heavy Ion Accelerator
Produces speeding particles to probe the nature of matter

ANU's heavy ion accelerator is a towering device that speeds up charged atoms to 10% of the speed of light. These speeding 'bullets' can then be used for a range of studies, including some high powered materials science.

The Heavy Ion Accelerator (or 14 UD accelerator) is one of the world's largest Van de Graaff generators (much like you would have seen at high school only larger, see below for a comparison). It's housed in a 40 metre-tall, steel and cement tower, and is used to generate enormous voltages of 15 million volts and more. This voltage is used to accelerate charged particles (ions) to 10% the speed of light. This is sufficient to overcome the strong electrostatic repulsion between atomic nuclei (which are positively charged so they repel), allowing the study of one of the fundamental but least understood forces - the strong nuclear force.

The Particle Accelerator supplies high energy ions for a variety of purposes ranging from studies on the structure of the nucleus, interactions between nuclei, materials science, global climate change, bio-medicine and archaeology.

Who runs it: The accelerator is operated by the Department of Nuclear Physics (part of the Research School of Physical Sciences and Engineering). It was commissioned in 1974 and has been constantly upgraded since then. Now it forms a part of the Department's Heavy-Ion Accelerator Facility, Australia's top nuclear physics laboratory. The Facility attracts some of the world's top scientists.

How does it work: To investigate the secrets of the nuclei of atoms you need to get them close enough so that they feel the strong nuclear force which only acts at short distances (one trillionth of a mm). The only way to achieve this is by striking them with other nuclei travelling with enormous energy. The accelerator is a machine that provides nuclei with such high energies.

The 14 UD accelerator works on the same principle as a Van de Graaff generator that you might have used in high school. The high school version is basically a metal sphere supported by a plastic tube. Inside the tube is a rubber belt that runs up and down in a closed loop. As the belt turns it generates a static electrical charge which is transferred to the metal sphere. Hold a piece of metal close to the sphere and you can observe a powerful spark jumping from the sphere to the metal. This is the same process of building up a charge by scuffing your feet on the carpet and then touching someone - ouch!!

The ANU's Van de Graaff generator is a bit more powerful. Instead of the rubber belt it contains three chains of nylon and stainless steel pellets. Each chain is over 20 metres long and whirs around at speeds over 50 km/hr. This generates electrical voltages in excess of 15 million volts. Working with such enormous voltages is tricky. The entire generator is housed in a massive steel tank filled with high-pressured, insulating sulphur hexafluoride gas.

Running down through the centre of the accelerator is an evacuated tube through which charged particles travel. Negative ions (negatively charged atoms) are injected into the top of the accelerator. They are accelerated (pulled) towards the positive terminal (positioned half way down). Here the speeding particles pass through a thin carbon foil which strips away the electrons around the nucleus. The atom is now positively charged and is repelled away from the positive terminal to the bottom of the accelerator gaining further energy.

A beam of speeding nuclei emerges from the bottom of the accelerator for use in a range of investigations. Magnets steer the beam of nuclei into one of several beam lines, each equipped with different devices and detectors for different experiments.
Many of the beamlines are involved in studies of the nucleus. One beam line passes through a second accelerator, a superconducting LINAC, which further increases the energy of the particles. These nuclei are travelling fast enough to fuse with heavier nuclei, providing a window into the sub-atomic world of the nucleus.

Another major area of research that uses the speeding bullets being produced by the particle accelerator is materials science. There are two broad areas of materials science being pursued:
Characterising semiconductors

Accelerator Mass Spectrometry

So the accelerator is actually only one component in a long line of sophisticated devices that together make up the Heavy Ion Facility.

More information: ANU Department of Nuclear Physics: Accelerator Facilities