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College Park, Maryland      June 6 - 10 , 2004

M2-D3 (11:15 AM): High-Pressure Neutron Scattering and the SNAP Instrument at the SNS (Invited)

R. J. Hemley (Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA), John Parise (Departments of Geosciences and Chemistry, State University of New York, Stony Brook, NY 11794) Chris Tulk (Spallation Neutron Source and Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831) and Ho-Kwang Mao (Geophysical Laboratory)

Research on materials under pressure is experiencing impressive growth in a number of new areas. The SNAP (Spallation Neutrons And Pressure) facility, the high-pressure instrument at the Spallation Neutron Source (SNS), is poised to capitalize on the many recent developments in the study of materials under pressure. The project involves the creation of a unique instrument that will utilize the high neutron flux of the SNS together with state-of-the-art high-pressure devices and advance the current pressure range of neutron studies well beyond present limits (tens of GPa), making possible many new classes of experiments. The facility will enable studies of a wide variety of new scientific problems involving matter under a broad range of pressures and spanning physics, chemistry, geoscience, planetary science, materials science, and bioscience. The instrument will be designed for single-crystal and powder diffraction measurements, with a flexible detector system and space for focusing optics, ancillary on-line measurements, and sufficient area downstream for a second station. An important recent advance is the development of new K-B focusing optics for neutrons that can now produce beam sizes down to 100 x 100 μm. Moreover, the creation of the SNS is taking place just at a time when radically new pressure cell designs will vastly broaden the number of techniques available for routine studies of materials over a broad P-T range, to well above megabar (> 100 GPa) pressures, while allowing unprecedented resolution, accuracy, and sensitivity at all conditions. A new generation of large volume gem-anvil devices based on moissanite (SiC) and single crystal diamond, including new single crystal diamonds produced by chemical vapor deposition, is becoming available. In the intermediate pressure range (< 30 GPa), devices such as the Paris-Edinburgh and ZAP cells will be used, and high-precision measurements at lower pressures (~ 1 GPa range) will be done with gas apparatus. These high-pressure devices will be coupled with the high-pressure instrument to give maximum performance, with the high-pressure facility also providing core support for high-pressure activities at other instruments at the SNS.

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