Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session H38: Focus Session: X-ray and Neutron Instruments and Sciences I |
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Sponsoring Units: GIMS Chair: Carolyn MacDonald, State University of New York at Albany Room: Colorado Convention Center 501 |
Tuesday, March 6, 2007 8:00AM - 8:36AM |
H38.00001: Probing Magnetic Materials Using Synchrotron Radiation and Phase Retarding Optics Invited Speaker: Synchrotron radiation has become an essential tool in the study of magnetic materials. The utility of x-ray measurements arises from the fact that the resonant and polarization properties observed near core-level resonances probe the valence-electron spin and orbital properties in an element specific manner. Critical to enabling such studies, however, has been the ability to easily manipulate the polarization of the x-ray beam. Circularly polarized x-rays pay a particularly important role, due to their coupling to the net ferromagnetic moment in a material. This talk will focus on how phase retarding optical elements can be used to tailor the focus on how phase retarding optical elements can be used to tailor the x-ray beam polarization in order to enable various types of magnetic measurements. Examples of magnetic spectroscopy, scattering, and imaging measurements employing such optics will be presented. [Preview Abstract] |
Tuesday, March 6, 2007 8:36AM - 8:48AM |
H38.00002: Probing the breakup of high-speed liquid jet by ultrafast x-ray microimaging. Jin Wang High-pressure high-speed sprays have vast industrial and consumer applications that penetrate to very aspect of the society. Despite their longstanding multitude of uses, the fundamental physics that governs the spray flow formation in high-speed jets is not well understood. Experimentally, the difficulty is due, in large part, to a lack of information about the composition of spray plumes close to the nozzle, such as liquid breakup mechanism and spray mass distribution. Traditional visualization tools like visible-light-based imaging have not been effective. To date, theoretical and computational studies of the sprays have proven to be extremely difficult, if not impossible, to carry out. We report here the development of x-ray-based microimaging technique to visualize the breakup of optically opaque high-speed jets in the near-nozzle region. The quantitative near-nozzle spray characteristics can serve to validate primary liquid breakup models and be used as indispensable initial and boundary conditions for spray atomization processes in further downstream areas. [Preview Abstract] |
Tuesday, March 6, 2007 8:48AM - 9:00AM |
H38.00003: X-ray imaging of nickel-based microstructured superalloys using synchrotron radiation Naji Husseini, Divine Kumah, Codrin Cionca, Roy Clarke, Jianzhang Yi, Christopher Torbet, J. Wayne Jones Nickel-based superalloys are used in harsh environments such as airplane turbines and nuclear power plants for their high temperature stability and resilience to oxidation and corrosion. These superalloys grow via directional solidification along the $<$001$>$ orientation and assume a dendritic morphology along $<$100$>$, concentrating Ni into the dendrites and TaC elsewhere. 200 $\mu $m thick samples of Rene N5 were imaged in a transmission setup at Sector 7 of the Advanced Photon Source with high-intensity synchrotron radiation. The recorded intensity maps contain information about the elemental concentration with sub-micron resolution, enhanced by phase contrast near sharp compositional variations. These maps show vacancies and cracks in addition to linearly decreasing concentrations of Re and W out from the center. Interferences seen while rotating the sample reveal misorientations of the cores and strain between dendrites, while a full rotation permits 3D tomography. One-second exposure times allow observation of \textit{in situ} crack propagation induced by an ultrasonic fatiguer. [Preview Abstract] |
Tuesday, March 6, 2007 9:00AM - 9:12AM |
H38.00004: Full-Field Microscopy with Synchrotron Radiation Christoph Rau, Vasilica Crecea, Wenjun Liu, Ian Robinson A full-field X-ray microscope has been built at the UNICAT-beamline 34 ID-C at the Advanced Photon Source (APS), working with a Kirkpatrick-Baez mirror (KB) as condenser and a micro-Fresnel-zone plate (FZP) as objective lens. 50~nm-features have been resolved in a Nickel structure operating the microscope at a photon energy of 9keV. The KB system used as a condenser focuses approximately 63{\%} of the incoming intensity onto the sample spot, matching the aperture of the objective lens. For the latter we have a choice of gold micro-FZP having outer zone widths from 40 to 70~nm. Under these conditions the X-ray microscope provides 50-85~nm resolution and short exposure times due to the high efficiency of the KB-system. A field of view of 20x40 micron$^{2}$ can be imaged within a minute by scanning the condenser optic. First tomography experiments have been performed. We will also discuss other techniques such as cone and in-line phase contrast imaging. [Preview Abstract] |
Tuesday, March 6, 2007 9:12AM - 9:24AM |
H38.00005: Quantitative strain analysis of single crystals using x-ray topography Y. Zhong, Y.S. Chu, A. T. Macrander, S.F. Krasnicki The x-ray topography technique images diffraction intensity variations of a crystal. The use of a CCD camera enables the measurement of different spatial resolutions. Currently an x-ray topograph with spatial resolution of 1 micron has been achieved, but the quantitative data analysis has not been explored widely. Quantitative strain analysis on these images extends new capabilities in crystal study. We have developed methods to quantify strain information through topography data. We will present these methods and discuss related practical issues, such as advantages, sensitivities, and limitations. We first introduce the azimuthal rotation method, suitable for strain components along the surface normal direction. The analysis requires accurate image registration; therefore we use the cross correlation method. Next we introduce a method to obtain quantitative strain tensor using bright field lattice refinement. The application of these methods on materials study is shown. [Preview Abstract] |
Tuesday, March 6, 2007 9:24AM - 9:36AM |
H38.00006: Absorber Materials for Transition-Edge Sensor X-ray Microcalorimeters Ari-David Brown, Simon Bandler, Regis Brekosky, James Chervenak, Fred Finkbeiner, Naoko Iyomoto, Richard Kelley, Caroline Kilbourne, Frederick Porter, Enectali Figueroa-Feliciano, Tarek Saab, John Sadleir Arrays of superconducting transition-edge sensors (TES) can provide high spatial and energy resolution necessary for x-ray astronomy. High quantum efficiency and uniformity of response can be achieved with a suitable absorber material, in which absorber x-ray stopping power, heat capacity, and thermal conductivity are relevant parameters. Here we compare these parameters for bismuth and gold. We find that the thermal conductivity of these materials is highly dependent upon the thin film deposition technique. Furthermore, we briefly discuss the performance of our x-ray detectors when they possess cantilevered evaporated Bi/Au, electroplated Bi/Au, and electroplated Au absorbers. [Preview Abstract] |
Tuesday, March 6, 2007 9:36AM - 9:48AM |
H38.00007: Electronic Structure Studies of Ce-doped Gamma Detector Materials Andrew Canning, Rostyslav Boutchko, Stephen Derenzo, Lin-Wang Wang, Marv Weber Cerium doped materials such as the Lanthanum Halides represent some of the brightest known scintillators for the detection of gamma rays. The scintillation process in Cerium doped materials corresponds to the transition from a 5d to 4f state on the Cerium atom where the 5d and 4f states must lie in the gap of the host materials. We have performed electronic structure calculations for many different Cerium doped materials using density functional based methods to determine the positions of the 5d and 4f states relative to the valence and conduction bands of the host materials. We find good agreement with experimental results for the systems studied in particular for the Lanthanum Halides. Our theoretical calculations will be used as a first step screening for candidate new detector materials. This work is funded by the Dept. of Homeland Security, Domestic Nuclear Detection Office. [Preview Abstract] |
Tuesday, March 6, 2007 9:48AM - 10:00AM |
H38.00008: Gamma-Ray Compton Light Source Development at LLNL Frederic Hartemann, Scott Anderson, David Gibson, Chris Hagmann, Micah Johnson, Igor Jovanovic, Mike Messerly, Jason Pruet, Miro Shverdin, Aaron Tremaine, Dennis McNabb, Craig Siders, Chris Barty A new class of tunable, monochromatic gamma-ray sources capable of operating at high peak and average brightness is currently being developed at LLNL for nuclear photo-science and applications. These novel systems are based on Compton scattering of laser photons by a high brightness relativistic electron beam produced by an rf photoinjector. Key technologies, basic scaling laws, and recent experimental results will be presented, along with an overview of future research and development directions. [Preview Abstract] |
Tuesday, March 6, 2007 10:00AM - 10:12AM |
H38.00009: Design and characterization of a compact multi-detector gamma array for studies of induced gamma emission: spontaneous decay of 178m2Hf as a test case P. Ugorowski, R. Propri, S.A. Karamian, D. Gohlke, J. Lazich, N. Caldwell, R.S. Chakrawarthy, M. Helba, H. Roberts, J.J. Carroll Recent scientific attention has focused on the m2 isomeric state of Hafnium, 178m2Hf. The spontaneous decay of 178m2Hf takes the form of a cascade of gamma photons, totaling 2.4 MeV of energy per nucleus, or approximately 1.3 GigaJoules/gram. If all the decays were simultaneous, exawatt (10$^18$) energy outputs could be realized. A class of isomers called ``K-isomers'' has been studied to determine the possibility of xray-induced decay of the excited isomeric state. The purpose of the ``miniball'' detector system was to separate out possible induced cascades from the spontaneous decay cascades using nuclear calorimetry, in order to settle a recent scientific controversy involving claims of induced decay and counter-claims of null results. [Preview Abstract] |
Tuesday, March 6, 2007 10:12AM - 10:24AM |
H38.00010: Submicron Resolution Neutron Radiography R. Gregory Downing Imaging diverse materials such as biological and electronic samples at nanometer scales is of current importance; however, capable analytical tools are few. An entirely novel position sensitive neutron detector was conceived based upon illumination of a thin converter causing reactions that diametrically emitted two particles. The converter is carefully aligned between facing position-sensitive particle detectors. The neutron-induced reaction particles strike both detectors in near temporal unison. The nanosecond difference in arrival time uniquely reveals the energy of each particle. Knowing the initial energies of the particles from fundamental physics, the geometry of the system, and the residual energy of the particles then the precise spatial coordinates of the neutron reaction are determined. The data are deconvolved to form a temporal and spatial map of the neutron field illuminating the area of the converter. This detector promises spatial resolution that ranges from a few micrometers to tens of nanometers, an improvement 10 to over 100 times existing systems. Applications for the detector include radiography and tomography for a host of organic and inorganic material studies. A trial demonstration at the NCNR will utilize an intense conditioned neutron beam and high speed data processing capabilities. [Preview Abstract] |
Tuesday, March 6, 2007 10:24AM - 10:36AM |
H38.00011: Scientific Opportunities at OPAL, the New Australian Research Reactor Robert Robinson Australian physics is entering a new ``golden age,'' with the startup of bright new neutron and photon sources in Sydney and Melbourne, in 2006 and 2007 respectively. The OPAL reactor and the Australian Synchrotron can be considered the greatest single investment in scientific infrastructure in Australia's history. They will essentially be ``sister'' facilities, with a common open user ethos, and a vision to play a major role in international science. Fuel was loaded into the reactor in August 2006, and full power (20MW) achieved in November 2006. It is our plan to commence the formal user program in mid 2007, but commissioning experiments will have taken place well before then. The first three instruments in operation will be a high-resolution powder diffractometer (for materials discovery), single-crystal diffractometer (for small-molecule crystallography) and a strain scanner (for mechanical engineering and industrial applications). These will be closely followed by four more instruments with broad application in nanoscience, condensed- matter physics and other scientific disciplines. Instrument performance will be competitive with the best research-reactor facilities anywhere. To date there is committed funding for 9 instruments, with a capacity to install a total of $\sim$18 beamlines. An update will be given on the status of OPAL, its thermal and cold neutron sources, its instruments and hopefully the first data. [Preview Abstract] |
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