NBS is Completing New Cold-Neutron Source
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For the past 10 years, U.S. scientists could participate in research using high intensity — •* "cold-neutron" sources only by traveling to the Institut Laue Langevin in Grenoble, —^ France. There, they were able to take advantage of open time available on the ' joint French-German-British reactor—but ., only after the research needs of scientists from the sponsoring European nations had J.^ been met. In recent years, however, "increased (European) demand for the most ! frequently used experimental instruments has virtually frozen out the U.S. scientists," —•* notes Lyle H. Schwartz, director of the National Bureau of Standards' (NBS) In~'*""/ stitute for Materials Science and Engi, neering, in Gaithersburg, MD. Butadaptations to the NBS research reactor, which -v should be completed within a few months, will provide U.S. researchers with a major —•» new domestic source of cold neutrons. Coupled with a recent doubling of the —~J r e a c t o r ' s p o w e r (to 20 m e g a w a t t s ) , Schwartz says "the elements are now in * place for establishment of a world-class cold-neutron research facility which would bring to U.S. scientists the capabilities for studying advanced materials now primarily reserved to Europeans."That is, in fact, the —< Reagan administration's plan. A $10 million request in the FY 1987 budget that the President sent to Congress would go to initiate construction of a new $27 million - * facility to make more efficient use of the «--( new NBS cold-neutron source. Why Cold Neutrons? To make precise structural measurements with neutrons, one should try to match as closely as possible the wavelength of the radiation to the structure being studied. The atomic-scale wavelengths of neutrons usually emanating from the NBS research reactor make them best forstudy.,V ing atomic structure. Neutrons cooled to temperatures approaching absolute zero, however, have longer wavelengths, making them better suited for studying such things as the molecular structure of polymers, defects in advanced ceramics, protein conformations in biomolecules, the motion of molecules on chemical catalysts, defects causing metallic structures to fail, and sensitive, nondestructive depth profiling of defect concentrations in semiconductor devices. In fact, Schwartz says, such studies "cannot be properly made by any other means." The new NBS cold-neutron facility will "chill" neutrons to this longer-wavelength regime. "In many instances," Schwartz says, "the expected results will allow the developmentof primary reference materials which
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will be used for calibration of secondary test methods." In the 1970s, small-angle neutron scattering (SANS)—a technique best done with very cold neutrons—"stimulated dramatic advances in our understanding of the structure of polymers and biomolecules," according to Schwartz. Although a modest cold-neutron source has existed at Brookhaven National Laboratory since 1980, most of the experimental work with cold neutrons has been conducted in Europe, where there are extensive cold-neutron faciliti
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