New Measurements Using Neutrons: Benefits of the Spallation Neutron Source
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The Spallation Neutron Source (SNS) proposed by the Department of Energy for ORNL will be a world-class measurement tool for scientists and engineers. It is slated to begin operating in 2006. Several ORNL neutron scientists recently commented on the potential benefits of the SNS.
“Neutron scattering at neutron sources,” says John Hayter, “turns out to be the best, often the only, and sometimes the lowest cost, tool that scientists have to study the structure of and interactions among atoms in ‘real-life’ materials. The SNS is expected to fill gaps in our knowledge because its pulsed neutron beams will be the most intense in the world, providing more neutrons per pulse than any other source.”
To make measurements using neutron scattering, neutron detectors are needed to measure the angles and energies of neutrons deflected from experimental targets. Work is under way at the Laboratory to develop improved neutron detectors using fiber-optic and semiconducting technologies. Led by Thomas Mason, SNS scientific director, ORNL researchers are working with Argonne National Laboratory researchers to design state-of-the-art neutron spectrometers and diffractometers that will be used at the SNS.
Because the SNS will be the world’s brightest source of neutrons, it will allow scientists to study very small samples that cannot be examined using current technologies. “Sometimes only small samples are available,” says Hayter. “A material may be so new that little is available. Or it might take too long and cost too much to generate a larger sample.”
“The ability of neutrons to precisely locate light atoms, particularly hydrogen, in small quantities of samples containing large biological molecules, such as proteins, should be important to the pharmaceutical industry,” says Gerard Bunick. “The SNS will be useful for studying mechanisms of protein activity and understanding how to design drugs to combat diseases by blocking critical protein functions in disease-causing bacteria and viruses.”
The SNS will allow scientists to follow the movements of molecules in a lubricant when it is repeatedly heated and squeezed on a bearing. It will enable studies of other complex fluids, such as blood, and soft materials, such as the permeable walls of body cells. “Understanding these materials at the molecular level using the SNS could speed the development of time-released drug-delivery systems that target specific parts of the body,” says Bill Hamilton. “Such drugs might be contained in vesicles, or membrane sacs within sacs, whose walls would be broken down by body chemicals, gradually releasing the drug in precise doses when and where it is needed. SNS studies also could speed development of artificial blood made of vesicles that mimic the action of human blood cells.” Knowing how atoms are arranged in new crystalline compounds with known properties is the key to understanding how to modify materials to make them work in desired ways. Such specially tailored materials could be used to make a faster electronic device or a longer-lasting artificial hip or knee joint.
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| Nobel Laureate Clifford Shull was among the ORNL researchers who pioneered neutron scattering by using neutrons from the Laboratory’s Graphite Reactor. |
“Neutron scattering is a powerful tool for determining crystal structure,” says Bryan Chakoumakos. “It also reveals changes in structure while a material is exposed to changing temperatures, pressures, or other environmental influences. It could help a ceramic engineer design a new material for cookware that won’t break when heated up. It could help geologists develop more accurate computer models for understanding large-scale earth processes, such as earthquakes, crustal tectonics, and the geomagnetic field.”
Thanks to neutron studies of atoms in magnetic materials, the world is benefiting from credit cards, audiotapes, videotapes, computer disks, and compact discs. “The SNS will help researchers continue to develop smaller, lighter, and stronger magnets and create useful magnetic materials as small as thin films and single files of atoms,” says Herb Mook, head of the Neutron Scattering Section in ORNL’s Solid State Division. “It will also enable scientists to determine the structure of high-temperature superconducting materials and the effects and behavior of magnetic fields in respect to these materials. SNS neutron data will be useful in developing high-current superconducting materials for underground transmission lines and very high-field magnets for particle accelerators and medical imaging devices.”
Because of environmental concerns and other barriers to commercializing new polymers, the plastics industry is increasingly blending existing polymers to form a material with the best possible properties. “By using small-angle neutron scattering at the SNS or ORNL’s High Flux Isotope Reactor,” says George Wignall, “we will be able to determine quickly how well polymers will mix, how long they should be ground and compressed, at which temperature they should be melted together to get the best mixing, and which mixtures will form the best products.”
If interest picks up in recycling plastics to slow the need for new landfills and to recover resources, the SNS could be particularly useful for practical polymer research. “It could help scientists understand which polymers can be melted down and mixed—and which can’t—to form useful polymer blends,” Wignall says. “It can help us determine how compatible different plastic components are, design strategies for reprocessing waste plastic, and evaluate the usefulness of the resulting blend material.”
Neutrons can be used to map an engine part or boiler material for residual stresses that predispose it to cracking, wear, accelerated chemical attack, and even failure during use. “Engineers want to know when a part is likely to fail and whether use of different materials and manufacturing processes, such as heat treatment, would produce a part that will last longer,” says Steve Spooner. “Neutron scattering results combined with computer models can provide these answers. The SNS will allow effective measurements of residual stresses in composites, which are being used increasingly to make cutting tools, aircraft structures, and engine parts because they are stronger and lighter than other materials. Neutron measurements of microscopic stresses in samples made different ways will help identify the manufacturing processes that produce the strongest composites.”
“The SNS will be a very sensitive tool for locating embrittling hydrogen atoms in weldments and turbine blades, imaging the location and density of hydrocarbons in fuels and lubricants in operating engines, and characterizing the migration of water in cements and rock,” says Cam Hubbard. “It will permit measurement of temperature in difficult-to-reach locations, such as the crown of a piston in an operating engine.”
To build a large engineering marvel such as a safer, more efficient turbine jet engine, researchers will rely on information from the SNS. It will help them better understand how metallic alloys in turbine blades behave under extreme stress at a microscopic level.
“Neutron scattering began at ORNL in the late 1940s with the pioneering research of Ernie Wollan and Clifford Shull, work for which Shull received the 1994 Nobel Prize in Physics,” says Bill Appleton, former associate director for the SNS and now ORNL’s deputy director for science and technology. “The Laboratory has continued and expanded that work ever since. Now, a worldwide community of scientists and engineers use neutron scattering. Their contributions have given us marvelous new materials, new knowledge, new drugs, and new products that have boosted the American economy. To continue these extraordinary advances, we need precise measurements of materials at the molecular level—measurements that only an extraordinary tool like the SNS can provide.”
Neutrons have a neutral charge, but their impact on the world should continue to be positive.
| The Joint Institute for Neutron Sciences will consist of meeting facilities, laboratories, a communication center, and housing for researchers from university, industrial, and government laboratories using the SNS. | Shampoo is one of many complex fluids studied with neutrons whose molecular structure changes as a one-directional force is applied, making the thick liquid thin enough to spread through hair. | Healthier, low-fat foods (like certain types of ice cream) that have better taste and texture will be made with guidance from neutron scattering. |
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