Probing past and future materials with neutrons
Key text
This topic is sponsored by the Australian Research Council Molecular and Materials Structure Network.
Over a hundred years after the Kelly gang were captured, researchers have been able to say how the famous armour was made.
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You will get more from this topic if you have mastered the basics of atoms and molecules – these links will take you to an annotated list of sites with helpful background information. |
The key to finding out how the armour was made lies in the temperature the metal was heated to. Probing the intact armour with x-rays and neutron beams revealed details about the structure of the molecules and its composition. The analyses suggest that the steel was heated to about 750 degrees Celsius and what type of steel it is (more about the armour later).
The same type of analysis that was used on the Kelly gang armour can be used to study all sorts of new and old materials. How are neutrons and x-rays used to study materials?
Complementary ways of probing molecules and materials
While most people have heard of X-rays being used to probe the atomic structure of materials and molecules, the use of neutron beams is not so well appreciated. This is in part because the most common ways of producing a beam of neutrons is through nuclear fission inside a nuclear reactor. It's a difficult and expensive process, and not one that is easily set up in the back of the lab. By contrast, it's relatively easy to produce and work with many forms of X-rays. Consequently, there are far fewer places around the world equipped for neutron studies than there are for X-ray analysis.
However, because neutrons interact with matter differently from X-rays there are enormous advantages in using both techniques. And now that Australia is establishing a world-class neutron beam facility in Sydney there are new opportunities opening up for neutron studies on molecules and materials (Box 1: Analysing the old and the new).
Why is molecular and atomic structure important?
Understanding the arrangement and type of atoms in molecules is the key to unlocking their potential. That's because the behaviour of the molecule is governed by its three dimensional structure and its composition. For example, understanding the structure of molecules is vital in working with proteins, viruses and DNA. It's the basis of rational drug design and has been used in the creation of the first anti-flu drug Relenza and in the HIV protease inhibitors.
Understanding the arrangement and type of atoms is also central to our understanding of the behaviour of many materials. Our ability to develop and work with many advanced materials such as micro-magnets, hydrogen storage materials, novel metal oxides, superconductors, photonic devices, molecular switches and sensors is based on our ability to determine and model their fine atomic structure.
The science of analysing the structure of molecules has come a long way in the past 100 years (Box 2: The development of neutron beam science). It began with the use of X-rays to probe the crystal structures of materials, but another way is with beams of neutrons.
Neutron beams versus X-rays
Neutrons are sub-atomic particles that have no electric charge – they're neutral – and this allows them to interact with the nucleus of an atom. Neutrons can reveal the position of the nucleus itself, which makes up a tiny fraction of the volume of an atom. X-rays, on the other hand, are a form of electromagnetic radiation. They are scattered by electrons and reveal the position of the electron cloud surrounding the nucleus of an atom.
Advantages of neutron analysis
When a neutron beam hits a sample, 80 to 90 per cent of the neutrons pass through the sample, some 'scatter' and a very small number are absorbed. The angle at which the neutron beam hits the sample and its energy affect the 'scattering' and the type of information that can be gained. The scattering of neutrons can be elastic or inelastic. Elastic scattering means the neutrons change direction but not speed. Elastic neutron scattering is used to study atomic and molecular structures. Neutrons can also scatter inelastically, which means they change both speed and direction. Inelastic scattering is used to study the motion of atoms inside materials.
Heavy atoms scatter X-rays more effectively than light atoms, and when light atoms like hydrogen are close to heavy atoms it is difficult to determine their exact position. Neutron scattering varies from one nucleus to another and is much better at picking up lighter atoms.
Because neutrons scatter from collisions with nuclei they penetrate further into materials than X-rays. This makes it possible to study samples inside large pieces of equipment such as aircraft engines or under more extreme pressures and temperatures.
Neutrons also behave like tiny bar magnets and can be used to investigate the magnetic properties of materials such as superconductors.
And, if all that wasn't enough, because neutrons have an energy similar to the vibrational energy of atoms in solids and liquids, they can be used to measure in detail the motion of atoms in molecules.
Australia's new research reactor
Related site: ANSTO’s nuclear research reactor
Presents a series of questions and answers about the OPAL research reactor.
(Australian Nuclear Science and Technology Organisation)
New opportunities in neutron beam science are opening up for Australian researchers with the commissioning of the OPAL research reactor by the Australian Nuclear Science and Technology Organisation at Lucas Heights in Sydney. The first uranium fuel was loaded into the reactor in August 2006. The neutron beam research facility at the OPAL reactor will be one of the world's best and researchers are building a communication network to ensure that the data provided by the facility's instruments can be accessed from all over the country (Box 3: Access for all).
Science with neutrons at the Bragg Institute
The Bragg Institute was established in 2002 to coordinate the scientific use of the OPAL reactor. Researchers at the Institute are developing nine neutron beam instruments that will use neutrons produced by the OPAL reactor. Each is named after an Australian native animal and records a different aspect of the interaction between a sample and the beam of neutrons. Some instruments record how many neutrons pass through the sample, while others measure neutrons being reflected by the sample.
Back to the armour
So what did the analysis of the armour reveal? The x-ray analysis indicated that it was heated to 750 degrees Celsius. This is significant because it suggests that the armour was made on a bush forge, not by a professional blacksmith who had equipment that could heat the metal to about 1000 degrees. And the neutron diffraction analysis indicated that it was made from a type of steel available in the 1880s, so the armour is likely to be the genuine article.
Boxes
1. Analysing the old and the new
2. The development of neutron beam science
3. Access for all
Related Nova topics
Synchrotrons – making the light fantastic
It's an advanced material world
Page updated July 2007.