Since the earliest experiments defining the properties of the neutron, accelerators have played an important role in providing neutrons for research and applications. Various researchers described specific examples of how neutrons are used for engineering magnetic materials, for measuring stress in machine parts, and for studying polymer processes in real-time during a Sunday morning session at the APS/AAPT Spring Meeting in Washington, DC. The session was jointly organized by the APS Division of Physics of Beams and the APS Forum on Industrial and Applied Physics.
Neutrons have provided an incisive tool for investigating the structure and morphology of materials ranging from complex fluids to magnetic multilayers to superconductors. Virtually every microscopic-level detail that is known about magnetic materials has been learned by scattering neutrons from them. For example, little would be known about excitations in quantum fluids, the spin-density- wave state of chromium, electronic back-donation in the bonding of organometallic compounds, or the conformation of proteins and DNA in nucleosomes without neutron scattering. This is because neutrons not only can penetrate deeply into materials, but they also have a magnetic moment which can probe an object's magnetic properties.
For many years, neutrons produced at accelerator facilities have complemented capabilities available from reactor-based sources. Now, however, according to James B. Ball (Oak Ridge National Laboratory), with the declining availability of reactor facilities, upgrades of existing accelerator facilities and proposed new, more powerful accelerator-based sources will be called upon to provide the necessary neutron capabilities. In April 1997, the APS Council issued a statement that expressed concern about an impending shortage of state-of-the-art neutron source facilities in the U.S. The text of this statement may be found on the APS home page under the Governance button.
Argonne's IPNS and the ISIS facility at Rutherford Appleton Laboratory in the U.S. are the two most powerful existing sources. The addition of another target is under discussion for ISIS, but Ball reported that the prognosis for approval was "not too promising." Over the next few years, several new neutron scattering spectrometers will be built at the Los Alamos Neutron Science Center (LANSCE), with plans to increase the neutron flux by a factor of three. Ball also discussed plans for next-generation facilities, namely the European Spallation Source, and the National Spallation Neutron Source, a next-generation facility at Oak Ridge proposed to be constructed by 2004.
According to Thomas Russell of the University of Massachusetts, Amherst, unique insight into the characteristics of bulk materials can also be gained by neutrons. More recently, neutron reflectivity has emerged as a premiere tool for the study of surfaces and interfaces. However, the flux limitations of current reactor and spallation sources have limited studies to the static, equilibrium behavior of materials. The next generation of neutron sources will increase neutron flux levels by more than an order of magnitude, leading to unprecedented advances in understanding not only the static behavior, but also kinetic and dynamic responses of materials.
Increasingly in recent years, neutrons are being applied to strategic or applied research, and product development. Roger Pynn of Los Alamos National Laboratory described several recent experiments conducted at LANSCE in temperature and particle velocity measurement in reacting high explosives; radiographic imaging with protons; chemical bonding in metal-dihydride complexes; and the structure of thin adhesive layers. These experiments have found many diverse applications, from the manufacture of beer cans, the development of new ceramic-reinforced metallics for the aerospace industry, and dynamic imaging of weapons hydrotests.
Joel McKeown of AECL Accelerators reported on recent advances in linac-based technology for industrial radiation processing, including applications such as sterilization and food irradiation. There are currently three such machines in operation, two of which are being used commercially.