Probing past and future materials with neutrons

Key text

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

Box 1: Analysing the old and the new

Neutrons can be used to analyse all sorts of materials. Here we describe just a few examples of the use of neutrons to analyse the structure and composition of new materials being developed and old materials dug up from the past.

Lung surfactants

Some premature babies have severe difficulty breathing and suffer from a condition called respiratory distress syndrome. The babies lack a protein that is usually present on the surface of the lung to prevent collapse of the air sacs and keep the lungs inflated.

Researchers at the University of Queensland have used neutrons to study the protein structure and its interaction with other molecules in the liquid at the surface of the lung. They found that the protein changes shape as it is compressed during breathing and hope that this information will lead to therapies to treat the condition.

Geopolymer concrete

Experiments at extremely high pressures and temperatures using neutrons are being done to find out how the composition of geopolymers changes their molecular structure and their physical characteristics. Geopolymers have possible uses as:

• geopolymer concrete to replace Portland cement;

• light weight composites that can tolerate high temperatures;

• materials to encapsulate radioactive waste for safe storage; and

• ceramics that can be cast in moulds.

Researchers at the University of Sydney are looking at the structure and dynamics of a new family of crystal materials that have the novel ability to contract, rather than expand, when warmed. The new crystals have units of molecules connected by bridges. Neutron scattering has shown that heating changes the molecular vibrations across the bridges, providing a possible explanation for the behaviour.

Microstructure of complex fluids

Many everyday household and personal care products are a complex mix of ingredients. The mixes are liquid-like or semi-solid depending on the temperature. Making products such as fabric conditioners, shampoos and shower gels can be more easily controlled if their structure is understood. The results of investigating the behaviour of the molecules at different temperatures have led to time and energy savings during their manufacture.

Genuine or fake?

Neutron diffraction is a new tool to study priceless archaeological artefacts or museum objects without destroying them. Genuine articles can be distinguished from fakes.

Traditionally, researchers have had to sacrifice some of the object for analysis by obtaining a core sample or grinding a sample to fine powder. Neutrons however can easily penetrate thick surface coatings or layers of corrosion of an intact object: the whole sample can be analysed rather than just a portion of it. Neutron diffraction can provide information about the mineral or metal composition, or orientation of crystals in the material. Deformations in the material or its crystal structure can provide valuable information about the objects history such as how it was made by ancient craftsmen.

Related site:

Council for the Central Laboratory of the Research Councils (UK)

• Lung surfactant 'squeeze out'
• Welded aerospace components and structures - taking the stress out of flying
• Flow phenomena in fluids
• Genuine or fake? Neutron diffraction for non-destructive testing of museum objects

Box 2: The development of neutron beam science

In 2002 the Bragg Institute was set up to foster links between academic and commercial research organisations within Australia and overseas. Researchers apply their expertise in the use of neutron beams to a wide range of fields including plastics, minerals, engineering, pharmaceuticals, electronics and biology.

The Institute was named in honour of the father and son team of William and Lawrence Bragg. They were awarded Australia's first Nobel Prize in Physics in 1915 for their work on the analysis of crystal structure using X-ray diffraction. This involves firing X-rays through the crystal lattice of a material. The atoms in the lattice cause the X-rays to scatter and by measuring the pattern of the emerging X-rays – the diffraction pattern – it's possible to calculate the arrangement of the atoms in the material. The Braggs first used X-ray diffraction patterns to determine the crystal structure of common salt, sodium chloride.

Of course, neutron diffraction wasn't available in 1915. Indeed, neutrons hadn't even been discovered. That didn't happen until 1932 when British physicist James Chadwick proved the existence of sub atomic particles found in the nucleus of the atom that were devoid of any electrical charge – neutrons. This discovery earned Chadwick a Nobel Prize in 1935.

The value of this new particle in probing the nature of matter didn't become clear until after 1945 with the development of nuclear reactors and the availability of usable amounts of neutrons, one of the products of nuclear fission. In 1946 the first neutron diffraction experiments were carried out and the field of neutron scattering developed over the following decades.

In recent years neutrons have been used increasingly to study the structure and movement of molecules in solids and fluids. Neutron scattering techniques are used in such widely differing areas as the study of the new ceramic superconductors, catalytic exhaust cleaning, elastic properties of polymers and virus structure.

Related sites:

• Nobelprize.org (Sweden)
  • The Nobel prize in physics 1915
  • The Nobel prize in physics 1935: Presentation speech

• Bragg scattering (Israel Institute of Technology, Department of Physics)

Box 3: Access for all

While Australia is lucky to have the OPAL reactor and neutron beam facilities, such technology is inherently expensive. It's too costly to replicate and maintain in multiple locations. This applies to many of the powerful instruments used to structurally characterise molecules and materials, including the Australian Synchrotron being developed in Melbourne.

The problem of access is now being addressed by recent technological developments in automation and the provision of internet access. The emerging technology will be used to build a collaborative network that provides internet access to instruments. A national database of resources will be available to allow users to interactively display, manipulate, analyse and discuss atomic structures across multiple monitors anywhere in the country.

Activities

• Access Excellence (USA)
  • Determining the structure of a molecule – students create a simple molecular model, draw it, and then try to reconstruct it. This shows students the difficulty in determining the structure of molecules from X-ray diffraction patterns.

• Earth Science Educational Resource Center (Stony Brook University, USA)
  • Bragg's law and diffraction: How waves reveal the atomic structure of crystals – provides a diagram showing two rays shining on two atomic layers of a crystal so that diffraction occurs. Students change angles and the distance between layers then click on 'Details' to determine if diffraction still occurs.

• The MATTER Project (UK)
  • Why diffraction? – an interactive tutorial showing different diffraction patterns and how a wave interacts with a single particle and a solid material. Also provides an exercise asking students to match the appropriate wavelength of radiation with the objects being studied.

• Science NetLinks (American Association for the Advancement of Science)
  • Carbon: Structure matters – students explore the molecular structure of matter and how it can affect the physical characteristics of a material.
  • Splitting the atom – students use the Internet to research the history of the splitting of the atom, and use that research to prepare a presentation on an aspect of that topic.
  • Dangers of radiation exposure – students learn about sources of high-energy radiation and calculate their exposure to ionizing radiation over the past year.
  • What do scientists do? – students develop an understanding of the diversity and nature of various science disciplines.

• MicroWorlds (Advanced Light Source, University of California, USA)
  Each of these modules provides background information and an activity relating to the atomic structure of materials.
  • Exploring the material world: Is carbon hard or soft?
  • Kevlar – the wonder material: I wonder what makes Kevlar so strong?

• Australian Nuclear Science and Technology Organisation
  • Nuclear science in society – provides an introduction to nuclear technology in Australia. Includes activities on the themes 'About radioactivity', 'The nuclear age', 'Using radiation' and 'Choosing nuclear futures'.

• Careers in science (Australia)
  • Choose your own adventure – illustrates to students how important and relevant scientific knowledge is to their future careers.

Further reading

Useful sites

The Bragg Institute (Australian Nuclear Science and Technology Organisation)

• What is neutron scattering?
  An introduction to the use of neutron scattering in different areas of science.
  http://ftp.ansto.gov.au/ansto/bragg/education/what.html

• Neutron scattering at ANSTO – neutrons are amazing!
  Provides answers to the following questions:
  • How can neutrons do all these things?
  • How are neutrons made?
  • How does ANSTO use neutrons?
  • How do neutrons help you?
  http://old-www.ansto.gov.au/ansto/bragg/education/neut_main.html

Australian Nuclear Science and Technology Organisation

• About OPAL
  Provides information about the OPAL reactor.
  http://www.ansto.gov.au/opal/home/about_opal.html

• OPAL research reactor – community version
  Profiles the OPAL reactor and the work of some of the researchers at ANSTO. A science–business version of the brochure is also available.
  http://www.ansto.gov.au/__data/assets/pdf_file/0020/3557/OPALlr.pdf

Nobelprize.org (Sweden)

• Press release
  Announces the 1994 Nobel Prize in Physics, awarded to Professor Bertram Brockhouse for the development of neutron spectroscopy and Professor Clifford Shull for the development of the neutron diffraction technique.
  http://nobelprize.org/nobel_prizes/physics/laureates/1994/press.html

• The Nobel Prize in Physics 1994
  Explains how neutrons reveal structure and dynamics, see more than X-rays and reveal inner stresses.
  http://nobelprize.org/nobel_prizes/physics/laureates/1994/illpres/

Uranium Information Centre Ltd, Australia

• Research reactors
  Describes the types of research reactors around the world, their uses, fuel used and spent fuel created by research reactors.
  http://www.uic.com.au/nip66.htm

• Australian research reactors
  Describes Australia's only research reactor, HIFAR, and its replacement OPAL.
  http://www.uic.com.au/nip31.htm

International Atomic Energy Agency

Provides a brochure, 'Research reactors purpose and future brochure', which includes the following sections:

• Research reactor applications
  http://www-naweb.iaea.org/napc/physics/ACTIVITIES/Research_Reactor_Applications.htm

• Science with neutrons
  http://www-naweb.iaea.org/napc/physics/ACTIVITIES/Science_with_Neutrons.htm

Australian Broadcasting Corporation

• George Dracoulis (In Conversation, 26 January 2006 ABC)
  An interview with George Dracoulis.
  http://www.abc.net.au/rn/science/incon/stories/s1550794.htm

• Lucas Heights new nuclear reactor (The Science Show, 30 August 2003)
  Looks at some of the concerns about the new research reactor at Lucas Heights in Sydney.
  http://www.abc.net.au/rn/scienceshow/stories/2003/921316.htm#

• Kelly gang armour (Catalyst, 21 August 2003)
  Reports on research showing how the famous armour was made.
  http://www.abc.net.au/catalyst/stories/s929067.htm

• Australia's new nuclear reactor: Do we need it? (Earthbeat, 23 February 2002)
  Questions the need for a new research reactor in Australia.
  http://www.abc.net.au/rn/science/earth/stories/s489492.htm

• New reactor (Catalyst, 14 February 2002)
  Asks why Australia is buying a new nuclear reactor.
  http://www.abc.net.au/catalyst/stories/s476001.htm

Glossary

alloys. Metal mixtures with greater strength, hardness or malleability than their component metals. The ratio of each component determines the properties of the alloy. Modern alloys may be created by adding just a few per cent of another metal.

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).

ceramics. Are inorganic, non-metallic solids processed or used at high temperatures. A ceramic is made by combining metallic and non-metallic elements. Traditional ceramic products such as clay pots and chinaware are hard, porous and brittle. Modern ceramics are used to create bones and teeth, cutting tools or to conduct electricity. For more information see Advanced ceramics (A to Z of Materials) and About ceramics (The American Ceramic Society).

colloids. Particles dispersed in a different phase, so that they do not easily filter or settle. The simplest case of particles dispersed in water is known as a colloidal dispersion. Examples of colloids include smoke (fine liquid droplets or solid particles in a gas), homogenised milk (fine droplets of fat in an aqueous phase) and paint (fine solid particles in a liquid).

composites. Composite materials are formed by combining two or more materials that have quite different properties. The different materials work together to give the composite unique properties, but within the composite you can easily tell the different materials apart – they do not dissolve or blend into each other. One material (the matrix or binder) surrounds and binds together a cluster of fibres or fragments of a much stronger material (the reinforcement). For more information see our Nova topic Putting it together – the science and technology of composite materials.

DNA (deoxyribonucleic acid). The nucleic acid forming the genetic material of all organisms with the exception of some viruses which have RNA. DNA is present in the nucleus and other organelles such as mitochondria and chloroplasts.

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.

emulsions. Small droplets of oil dispersed in water or small droplets of water dispersed in oil. Since oil and water don't mix, emulsifiers are added to produce the small droplets and to prevent the oil and water phases from separating. Emulsifiers work by changing the surface tension between the water and the oil, thus producing a homogeneous product with an even texture. Examples of emulsions include butter and mayonnaise.

membrane. A thin, pliable sheet or layer. Biological membranes consist of a double layer of lipids – organic molecules that are not soluble in water – and associated proteins. Biological membranes are selectively permeable – not all molecules can pass through the membrane. For more information see Structure of plasma membranes (British Broadcasting Corporation, UK) and Cell membranes (Kimball's Biology Pages, USA).

neutron. A particle having no charge that is a constituent of an atom. It has a mass similar to a proton.

nuclear fission. Also referred to as atomic fission. The process by which large nuclei are split into two parts, by bombarding them with neutrons, in order to release large amounts of energy.

polymer. Polymers are large molecules that are made up of many units (monomers) linked together in a chain. There are naturally occurring polymers (eg, starch and DNA) and synthetic polymers (eg, nylon and silicone). More information can be found at The basics – polymer definition and properties (Plastic Resource, USA), Introduction to polymers (Case Western Reserve University, USA) and History of polymers and plastics for teachers (Hands On Plastics, American Plastics Council).

protease inhibitors. Molecules that block the function of enzymes that degrade proteins. They are classified either by the type of protease they inhibit or by their mechanism of action. Protease inhibitors are used in the treatment of HIV, where they prevent the activity of a protease that makes the active form of an enzyme used to make more viral particles. For more information see Disarming a deadly virus: Proteases and their inhibitors (National Academy of Sciences, USA).

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).

Relenza. The commercial name for an anti-influenza drug (zanamivir) that binds to and inactivates an enzyme, preventing the formation of new viral particles. For more information see CSIRO research leads to effective treatment against the flu virus (CSIRO, Australia).

superconductor. A substance that has no resistance to the flow of an electric current. Superconductors currently require very low temperatures to function. They can be used for energy storage, storing and retrieving digital information, medical imaging machines and friction free transport. For more information see What is superconductivity? (How Stuff Works, USA) and Superconductor information for the beginner (Superconductors.org).

uranium. A radioactive heavy metal. The natural element is a mixture of different isotopes or atomic forms. The isotope uranium-235 is used in nuclear non-breeder reactors.

virus. A submicroscopic infectious agent consisting of a nucleic acid (DNA or RNA) molecule surrounded by a protein coat. Viruses cannot replicate outside a living cell. More information can be found at How viruses work (How Stuff Works, USA).

X-ray. A high energy form of electromagnetic radiation with very short wavelengths (less than 1 x 10^-8 metres). For more information see How X-rays work (How Stuff Works, USA) and From X-rays to synchrotron light (ELETTRA Synchrotron Light Laboratory, Italy).

X-ray crystallography. X-ray crystallography involves firing X-rays through the crystal of a molecule to produce a diffraction pattern. This pattern provides information on the structure of that crystal. For example, X-ray crystallography helped scientists discover that the DNA molecule exists as a double helix. For more information see Introduction to crystallography (Matter, UK).