Although one of the most fascinating aspects of the Spallation Neutron Source is its creation of neutron beams, the big payoff for scientists when it comes on line in 2006 will be the arrival of those neutrons at a suite of state-of-the-art instruments. The SNS, which will offer 10 times more neutrons per second per unit area than comparable sources, will be an unparalleled resource for materials scientists around the world. Thanks to its instruments, SNS will be betterby factors of even hundredsthan any neutron research facility currently available.
“The high intensity of neutron beams is important, because it will allow researchers more flexibility with their analytical tools,” says Kent Crawford, an Argonne National Laboratory researcher assigned to the SNS Project’s Experimental Facilities Division. “Also, the more intensity we have, the higher resolution we can attain.”
Crawford says the 10- to 12-times improvement in beam intensity will grow into, in some cases, an exponential improvement in instrumentation that will be available to materials researchers. “We can take advantage of the most current technology in instrument design,” he says. “Some of the instruments will perform from 100 to several thousand times more effectively than instruments available now.”
That means that for the first time researchers will be able to solve problems and explore areas that have up to this point been out of the reach of existing instruments. Here are six of them:
What are the underlying mechanisms in technologically important materials properties such as ferroelectricity, piezoelectricity, and magnetorestriction? Stroboscopic diffraction studies on the SNS powder diffractometer, with a time resolution of 0.5 milliseconds or better, will allow detailed, time-resolved investigations of a wide range of metal-oxide displacive transitions. Such transitions are at the heart of these technologically important properties, and this detailed understanding may lead to the development of new materials with properties tailored for specific applications.
What are the physical processes responsible for high-temperature superconductivity? Neutron scattering studies have identified many features of high-temperature superconductors, such as charge and spin ordering. However, the relationship between these features and superconductivity is far from understood. The wide-angle and high-resolution chopper spectrometers at SNS together provide an ideal energy and resolution range to study the dynamics in these systems, and the increased intensity will expedite the observation of these features.
How are proteins organized and how do they move and function in biologically important systems such as cell membranes? Time-resolved experiments on the SNS’s small-angle neutron scattering instrument may provide important information about the dynamics of such molecules. The SNS reflectometers will enable depth-resolved studies of two-dimensional structures such as proteins embedded in cell-membrane analogues. Similar types of measurements could probe the organization of arrays of nano-structures deposited on substrates.
How can component processing be improved to provide more useful engineering properties? Localized stresses introduced into materials and components during processing can significantly affect their performance. The SNS engineering materials diffractometer will incorporate greatly improved capabilities for mapping such localized stresses. The new capabilities will enable studies of fabrication processes that are impractical using current instruments. In-situ measurements to investigate how stresses change when the component is in use will also be possible for the first time.
What are the structural and dynamic properties of materials under such extreme conditions as those found deep in the earth, at the depths of the ocean, or in the cores of planets or other interstellar bodies? Material properties at the earth’s core-mantle boundary are very poorly understood. The mega-bar initiative planned in conjunction with the SNS ultrahigh-pressure diffractometer should make it possible to do neutron diffraction at pressures of 100 Gpa, enabling detailed structural studies in those conditions.
The other planets in our solar system are composed mostly of ice at very high pressures. Although very-high-pressure phases of ice are currently poorly understood, the SNS ultrahigh-pressure diffractometer may enable new understanding of the mineralogy and petrology of non-terrestrial planets. Studies at SNS should also help explain effects on icy interstallar bodies during decomposition and impact by objects in the cosmos.
How can the magnetic properties of thin films be optimized to improve the performance of magnetic memories and magnetic recording media? A polarized-beam reflectometer, part of the initial instrument suite at SNS, will allow the nanoscience community to investigate magnetic and chemical density properties in surfaces, thin films, interfaces, and multilayer systems. Fundamentally new scientific insights will be important to the development of future thin-film-based applications, such as new magnetic memory technologies, magnetic recording media, and magnetic sensors for computers.B.C.
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