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Scientific Advances Made Possible by User Facilities - upmc

Scientific Advances Made Possible by User Facilities - upmc

Scientific Advances Made Possible by User Facilities -

Scientific Advances MadePossible by User FacilitiesGordon E. Brown Jr., 1,2 Georges Calas, 3 and Russell J. Hemley 4National scientific user facilities are becoming increasingly available tomany different scientific communities in a number of countries. Earthand environmental scientists are increasingly using these facilities tostudy a broad range of materials and processes under realistic P–T andenvironmental conditions at unprecedented levels of energy and spatialresolution and elemental and isotopic sensitivity. The results of these studiesare providing new insights into biogeochemical processes operating at Earth’ssurface as well as petrological, geochemical, and geophysical processes inEarth’s interior. The availability of national user facilities is changing scientificapproaches and is leading to multidisciplinary studies that were notpossible a decade ago.KEYWORDS: national scientific user facilities, synchrotron radiation sources,neutron sources, Earth sciences research.INTRODUCTIONDiscoveries in most areas of science come from observationsat different spatial scales, ranging from astronomicalto subatomic, using instrumentation that ranges in complexityfrom an optical telescope to a particle accelerator. Inthe Earth sciences, relevant spatial scales extend fromatomic to global, and instrumentation can be as simple as ahand lens and Brunton compass or as complex as a synchrotronlight source. The repertoire of available researchinstruments has expanded greatly during the past 20 to 30years because of the development of large-scale nationaluser facilities in many countries. These facilities, whichinclude synchrotron light sources, neutron sources, particleaccelerators, electron beam microcharacterization facilities,and nanoscale-science research centers, are having a majorimpact on research on materials of all types. Such facilitiesare being used to determine the structures, compositionalvariations, physical properties, and submicron-scale heterogeneitiesof Earth materials. Experiments are carried outunder conditions mimicking those in key geological environments,such as in Earth’s deep interior or at the interfacesbetween mineral particles and aqueous solutions insoils at Earth’s surface, where much of the chemistry relevantto the environment occurs. Many of these advancedtechniques and cutting-edge technologies are not generally1 Department of Geological & Environmental Sciences, StanfordUniversity, Stanford, CA 94305-2115, USA; e-mail:gordon@pangea.stanford.edu2 Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road,MS 69, SLAC, Menlo Park, CA 94025, USA3 Institut de Minéralogie et de Physique des Milieux Condensés,Universités de Paris 6 et 7, IPGP, 140 rue de Lourmel, 75015 Paris,France; e-mail: calas@lmcp.jussieu.fr4 Geophysical Laboratory, Carnegie Institution of Washington, 5251Broad Branch Rd NW, Washington, DC 20015, USA; e-mail:r.hemley@gl.ciw.eduavailable in university or individualinvestigator laboratories, butuser facilities make them availableto many scientific communities.User facilities also make possibleexperimental studies that wereimpossible prior to their existence.This article focuses on the role ofnational user facilities, particularlysynchrotron radiation and neutronsources, in Earth and environmentalsciences research and highlightssome of the discoveries suchfacilities have enabled in thesefields over the past decade.At the atomic scale, 3-D observationsrequire the use of electromagneticradiation of wavelengthssimilar to the bond distances between atoms (0.1–0.5nanometers) in the building blocks (unit cells) of crystals.Short-wavelength radiation, referred to as X-rays (withenergies ranging from about 100 eV to greater than 100keV), was first discovered in 1895 by Wilhelm Conrad Röntgen.Since that time, X-rays and X-ray diffraction (XRD)have revolutionized many areas of science, as demonstratedby the 18 Nobel Prizes in physics, chemistry, and medicineawarded from 1901 through 2005 that are directly linked tothe usage of X-rays. XRD has had a profound impact onmineralogy, having been used over the past 90 years todetermine the atomic structures of the 4000+ known minerals.XRD has also had a major impact on our knowledge of thematerials that comprise Earth’s interior through studies ofthe stability and phase transformations of minerals at pressuresand temperatures representative of Earth’s mantle (~0to 136 GPa and 1200 to 3600K). The high pressures andtemperatures can be generated using diamond anvil cells(DAC) and laser heating, respectively, permitting XRD andspectroscopic studies of mineral phases under in situ conditions(Mao and Hemley 1998; Bass et al. 2004). Large-volumepresses provide access to somewhat lower temperaturesand pressures, but the sample volume is larger than in aDAC. High P–T studies using these devices have revealedphase transformations and changes in mineral densities atpressures and temperatures corresponding to the depths ofmajor discontinuities in seismic wave velocities within thedeep Earth.XRD is not the only means of determining the atomic structureof matter. The elastic scattering of neutrons also providesthis type of information, with some advantages anddisadvantages. Advantages include the ability to distinguishbetween atoms with similar atomic numbers or betweendifferent isotopes of the same element. DisadvantagesE LEMENTS, VOL. 2, PP. 23–30 23FEBRUARY 2006

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