Next-Generation Neutron Sources
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Next-Generation
Neutron Sources
Thomas E. Mason, Masatoshi Arai, and Kurt N. Clausen Abstract This article gives an overview of current neutron-scattering facilities and illustrates the capabilities of third-generation sources that are now under development. The new science that is driving this development has been illustrated in the articles in this issue of MRS Bulletin and in a previous issue published in 1999 [MRS Bull. 24 (12) (1999) p. 14]. The scale of these facilities is such that only three of them are envisaged worldwide, in the Asia Pacific region, Europe, and America. Two construction projects, the spallation neutron sources in the United States (SNS) and in Japan (J-PARC), are now well under way, while the European proposal for a spallation source (ESS) is still awaiting a decision to start construction. Keywords: materials science, neutron scattering, neutron sources.
pare the new-generation spallation sources with present leading facilities, the capabilities of key instruments such as powder diffractometers, time-of-flight spectrometers, or small-angle neutron scattering devices were evaluated and assessed in depth. Source and instrument gains were considered separately. As a result, instrumentdependent gains in effective source strength ranging from a factor of 5–60 were identified.1 This is the biggest jump in source power, relative to leading facilities, ever experienced and will beyond doubt transform neutron scattering and revolutionize the use of the technique. The existing major sources for neutron scattering are shown in Table I, along with Web addresses from which more information can be obtained, including available instrumentation, instructions for obtaining research time, and recent progress reports on scientific accomplishments. Additional information on smaller sources can be found at www.neutron.anl.gov or www.neutron-eu.net. These Web sites comprise the most comprehensive description of the instrumentation and scientific opportunities available today.
The New Megawatt Neutron Spallation Sources Introduction Neutrons are one of the most powerful probes for making the arrangement of atoms visible and for measuring the forces between them. The potential performance of a neutron source is basically the product of two quantities—the source strength, which measures the flux of useful neutrons produced in the source, and the instrumentation factor, which measures how efficiently we can detect the scattered neutrons. The first neutron sources were research reactors, and a rapid progression in neutron-source performance followed the reactor developments in the 1940s, 1950s, and 1960s. At the end of the 1960s, this technology was fully mature, and since then, advances in the scientific utility of the technique have been derived mainly from improvements in instrumentation. Neutrons can also be produced by spallation, that is, through bombardment of a heavy atom with intense beams of highenergy protons (GeV or velocities 90% of the velocity of light). During the 1990s, accelerator technolog
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