Neutron scattering applied to materials problems

Abstract

Neutron scattering techniques for studying materials have been applied for more than 50 years, in part led by Clifford G. Shull and Bertram N. Brockhouse, who shared the 1994 Nobel Prize in physics. The award was given for their developments in studying both the structure and dynamics of materials. The application of neutron scattering to materials has received significantly greater attention in the last few years, due to the construction of the Spallation Neutron Source (SNS) at the Oak Ridge National laboratory. The SNS will provide unprecedented access to a wide variety of instruments designed for materials research. The idea for this series of articles originated during the 2005 TMS Annual Meeting. Two symposia were devoted to neutron scattering: Neutron Scattering in Materials Research; and Neutron Diffraction Characterization of Mechanical Behavior. the goal of these articles is to introduce techniques for studying materials using neutrons, particularly to answer what are considered traditional materials problems. The first article discusses structure and phase analysis. Neutrons may be used for diffraction, similar to x-rays. However, in certain circumstances, they bring particular advantages. For example, x-rays have difficulty 'seeing' light elements, particularly when heavier elements are present, whereas neutrons may scatter effectively from elementsmore » such as hydrogen and its isotopes. The scattering strength of neutrons is sensitive to the isotopic composition. This can be used to examine the influence of a particular element. Neutrons also interact magnetically, allowing their use for studying magnetic order in materials. Because neutrons are highly penetrating, in-situ investigations under special sample environments (e.g., temperature, magnetic field, high pressure) have become routine. The second article describes applications for studying residual stress and mechanical deformation. neutrons are better able to penetrate engineering components compared to x-rays so neutron diffraction is used to examine the spatial distribution of stress and texture. In-situ loading studies have allowed for a sensitive, nondestructive study of the deformation mechanisms. More recently, neutrons have been used to analyze the dislocation and subgrain structures due to deformation. neutrons are also well suited for the study of composite materials, as diffraction peaks from each phase are separated. The author describes the fundamentals and applications of inelastic neutron scattering. By measuring not only the change in wave vector, but also the change in energy, neutrons can probe the dynamics in materials. This is used for examining elastic properties, magnetic excitations, and other dynamics that affect both the response of materials to applied driving forces and the thermodynamic properties of materials. The last article discusses facilities. The user facilitates are almost as varied as the applications, with many different instruments at each major facility. The article discusses the various facilities and instruments, as well as how to apply for access to these facilities.« less