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Hard X-rays (hard + x-ray)
Terms modified by Hard X-rays Selected AbstractsHelioseismic analysis of the solar flare-induced sunquake of 2005 January 15MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007H. Moradi ABSTRACT We report the discovery of one of the most powerful sunquakes detected to date, produced by an X1.2-class solar flare in active region AR10720 on 2005 January 15. We used helioseismic holography to image the source of seismic waves emitted into the solar interior from the site of the flare. Acoustic egression power maps at 3 and 6 mHz with a 2-mHz bandpass reveal a compact acoustic source strongly correlated with impulsive hard X-ray and visible-continuum emission along the penumbral neutral line separating the two major opposing umbrae in the ,-configuration sunspot that predominates AR10720. At 6 mHz the seismic source has two components, an intense, compact kernel located on the penumbral neutral line of the ,-configuration sunspot that predominates AR10720, and a significantly more diffuse signature distributed along the neutral line up to ,15 Mm east and ,30 Mm west of the kernel. The acoustic emission signatures were directly aligned with both hard X-ray and visible continuum emission that emanated during the flare. The visible continuum emission is estimated at 2.0 × 1023 J, approximately 500 times the seismic emission of ,4 × 1020 J. The flare of 2005 January 15 exhibits the same close spatial alignment between the sources of the seismic emission and impulsive visible continuum emission as previous flares, reinforcing the hypothesis that the acoustic emission may be driven by heating of the low photosphere. However, it is a major exception in that there was no signature to indicate the inclusion of protons in the particle beams thought to supply the energy radiated by the flare. The continued strong coincidence between the sources of seismic emission and impulsive visible continuum emission in the case of a proton-deficient white-lightflare lends substantial support to the ,back-warming' hypothesis, that the low photosphere is significantly heated by intense Balmer and Paschen continuum-edge radiation from the overlying chromosphere in white-light flares. [source] Principles of Highly Resolved Determination of Texture and Microstructure using High-Energy Synchrotron Radiation,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Helmut Klein Abstract Diffraction imaging with hard X-rays (high-energy synchrotron radiation) using the detector sweeping techniques allows measurement of the texture and microstructure of polycrystalline materials with high orientation- and location-resolution. These techniques provide continuous two-dimensional images of different sections and projections of the six-dimensional "orientation-location" space. For the high orientation resolution case, it is possible to measure the orientation and location coordinates of up to 105 individual grains simultaneously. From these parameters, the grain size and shape can also be obtained, yielding the complete orientation stereology of the polycrystalline aggregate, which is required for its complete characterization. For the high location resolution case, the intensity at any point of the diagrams corresponds to a pole density as a function of the orientation-location space. [source] An algebraic algorithm for generation of three-dimensional grain maps based on diffraction with a wide beam of hard X-raysJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2004T. Markussen A reconstruction method is presented for generation of three-dimensional maps of the grain boundaries within powders or polycrystals. The grains are assumed to have a mosaic spread below 1°. They are mapped by diffraction with a wide beam of hard X-rays, using a setup similar to that of parallel-beam absorption contrast tomography. First the diffraction spots are sorted with respect to grain of origin. Next, for each grain the reconstruction is performed by an algebraic algorithm known as three-dimensional ART. From simulations it is found that reconstructions with a spatial accuracy better than the pixel size of the detector can be obtained from as few as five diffraction spots. The results are superior to three-dimensional reconstructions based on the same data using a variant of the filtered back-projection algorithm. In comparison with layer-by-layer type reconstructions based on the two-dimensional ART algorithm, as introduced by Poulsen & Fu [J. Appl. Cryst. (2003), 36, 1062,1068], the quality of the maps is found to be similar, provided that five to ten spots are available for analysis, while data acquisition with the three-dimensional method is much faster. The three-dimensional ART methodology is validated on experimental data. With state-of-the-art detectors, the spatial accuracy is estimated to be 5,µm. [source] A high sensitivity pinhole camera for soft condensed matterJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003Thomas Zemb A significant improvement in the sensitivity of a Huxley-Holmes design for a small angle X-ray scattering camera is obtained by separating the mirror and the monochromator. The "separated optics" camera described in this paper involves a long X-ray mirror close to a point X-ray source associated with a curved focusing crystal located close to the sample. The sample area is located at half the distance between the source and detector planes. Diffuse scattering produced by the mirror is not incident on the focusing crystal, thus reducing the background signal. Complete elimination of hard X-rays allows precise calibration and hence absolute determination of sample cross-section by means of a semi-transparent beam-stop. In pinhole geometry, the flux corresponds to a ca. 107 photons/s through the sample, collimated to q=10 -2 Å -1 in scattering vector range. This allows determination of scattered intensities of the order of 10 -3 cm -1, corresponding to the scattering related to isothermal compressibility of less than 0.1 mm of pure water. Values of absolute intensities for water as well as convenient widespread buffer solutions are shown, in order to be usable for calibration as secondary standards. As solid reference sample, the widely studied Lupolentm, a semi-crystalline polymer- is calibrated. The high- q limit (q, 4.5 nm,1 ) of a porous calcite sample can be used as a secondary standard for specific area determination of solid/solid or solid-liquid dispersions. [source] X-ray fluorescence microprobe imaging in biology and medicineJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 6 2006Tatjana Paunesku Abstract Characteristic X-ray fluorescence is a technique that can be used to establish elemental concentrations for a large number of different chemical elements simultaneously in different locations in cell and tissue samples. Exposing the samples to an X-ray beam is the basis of X-ray fluorescence microscopy (XFM). This technique provides the excellent trace element sensitivity; and, due to the large penetration depth of hard X-rays, an opportunity to image whole cells and quantify elements on a per cell basis. Moreover, because specimens prepared for XFM do not require sectioning, they can be investigated close to their natural, hydrated state with cryogenic approaches. Until several years ago, XFM was not widely available to bio-medical communities, and rarely offered resolution better then several microns. This has changed drastically with the development of third-generation synchrotrons. Recent examples of elemental imaging of cells and tissues show the maturation of XFM imaging technique into an elegant and informative way to gain insight into cellular processes. Future developments of XFM,building of new XFM facilities with higher resolution, higher sensitivity or higher throughput will further advance studies of native elemental makeup of cells and provide the biological community including the budding area of bionanotechnology with a tool perfectly suited to monitor the distribution of metals including nanovectors and measure the results of interactions between the nanovectors and living cells and tissues. J. Cell. Biochem. 99: 1489,1502, 2006. © 2006 Wiley-Liss, Inc. [source] A novel epitaxially grown LSO-based thin-film scintillator for micro-imaging using hard synchrotron radiationJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2010Paul-Antoine Douissard The efficiency of high-resolution pixel detectors for hard X-rays is nowadays one of the major criteria which drives the feasibility of imaging experiments and in general the performance of an experimental station for synchrotron-based microtomography and radiography. Here the luminescent screen used for the indirect detection is focused on in order to increase the detective quantum efficiency: a novel scintillator based on doped Lu2SiO5 (LSO), epitaxially grown as thin film via the liquid phase epitaxy technique. It is shown that, by using adapted growth and doping parameters as well as a dedicated substrate, the scintillation behaviour of a LSO-based thin crystal together with the high stopping power of the material allows for high-performance indirect X-ray detection. In detail, the conversion efficiency, the radioluminescence spectra, the optical absorption spectra under UV/visible-light and the afterglow are investigated. A set-up to study the effect of the thin-film scintillator's temperature on its conversion efficiency is described as well. It delivers knowledge which is important when working with higher photon flux densities and the corresponding high heat load on the material. Additionally, X-ray imaging systems based on different diffraction-limited visible-light optics and CCD cameras using among others LSO-based thin film are compared. Finally, the performance of the LSO thin film is illustrated by imaging a honey bee leg, demonstrating the value of efficient high-resolution computed tomography for life sciences. [source] A monolithic Fresnel bimirror for hard X-rays and its application for coherence measurementsJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2007Ullrich Pietsch Experiments using a simple X-ray interferometer to measure the degree of spatial coherence of hard X-rays are reported. A monolithic Fresnel bimirror is used at small incidence angles to investigate synchrotron radiation in the energy interval 5,50,keV with monochromatic and white beam. The experimental set-up was equivalent to a Young's double-slit experiment for hard X-rays with slit dimensions in the micrometre range. From the high-contrast interference pattern the degree of coherence was determined. [source] On the feasibility of large-aperture Fresnel lenses for the microfocusing of hard X-raysJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2006Werner Jark Like visible light, X-rays can also be focused by refraction in transmission lenses. For visible light this requires convex lenses while for X-rays one needs to use concave lenses instead. Both lens types can be lightened by the material removal strategy introduced by Fresnel, which results in a lens subdivided into zones. Until now, for the focusing of X-rays, stacks of standard lenses and of Fresnel lenses have mostly been produced. The first are dubbed compound refractive lenses, abbreviated as CRL. State-of-the-art systems of this kind now achieve almost theoretical performance for the focus size and the transmission. On the other hand, the latter Fresnel systems, which promise to provide larger apertures, are still in their infancy. This report discusses systematically the properties of two possible schemes for their realisation. It then compares the optimized apertures of these two schemes with those for CRLs. The best Fresnel lenses in this study are found to provide experimentally more than 50% of the expected refraction efficiency at 8.5,keV photon energy. The photon flux in their focus is then almost identical to that of perfect Be CRLs with the same focal length. This report will also interpret experimental data reported previously for other Fresnel lenses. [source] Small-gap insertion-device development at the National Synchrotron Light Source , performance of the new X13 mini-gap undulatorJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2004J. M. Ablett The National Synchrotron Light Source (NSLS) 2.8,GeV electron storage ring continues to set high standards in insertion-device research and development. The Chasman,Green NSLS lattice design provides for dispersion-free long straight sections in addition to a very small vertical , function. As the electron beam size is proportional to the square root of this function, a program to exploit this feature was undertaken more than a decade ago by implementing short-period small-gap insertion devices in the NSLS storage ring. The possibility of utilizing existing moderate-energy synchrotron radiation electron storage rings to produce high-brightness photon beams into the harder X-ray region have been realised using in-vacuum undulators. In this article the operation of a 1.25,cm-period mini-gap undulator, operating down to a gap of 3.3,mm within the NSLS X13 straight section, is reported. It is the brightest source of hard X-rays in the energy range ,3.7,16,keV at the NSLS, and replaces an in-vacuum undulator which had a more limited tunability. [source] X-ray magnetic circular dichroism imaging with hard X-raysJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2001K. Sato X-ray polarization-contrast images resulting from X-ray magnetic circular dichroism (XMCD) in the hard X-ray region have been successfully recorded for the first time. The apparatus used consisted of an X-ray polarizer, double X-ray phase retarders, and a high-spatial-resolution X-ray charge-coupled-device detector. The sample used was a hexagonal-close-packed cobalt polycrystal foil having a thickness of about 4,µm. The X-ray polarization-contrast image resulting from XMCD was observed at a photon energy of 10,eV above the cobalt K -absorption edge (7709,eV). The observed contrast in the image was reversed by inversion of the magnetic field. Furthermore, the contrast was reversed again at a photon energy of 32,eV above the cobalt K -absorption edge. [source] Imaging of cochlear tissue with a grating interferometer and hard X-raysMICROSCOPY RESEARCH AND TECHNIQUE, Issue 12 2009Claus-Peter Richter Abstract This article addresses an important current development in medical and biological imaging: the possibility of imaging soft tissue at resolutions in the micron range using hard X-rays. Challenging environments, including the cochlea, require the imaging of soft tissue structure surrounded by bone. We demonstrate that cochlear soft tissue structures can be imaged with hard X-ray phase contrast. Furthermore, we show that only a thin slice of the tissue is required to introduce a large phase shift. It is likely that the phase contrast image of the soft tissue structures is sufficient to image the structures even if surrounded by bone. For the present set of experiments, structures with low-absorption contrast have been visualized using in-line phase contrast imaging and a grating interferometer. The experiments have been performed at the Advanced Photon Source at Argonne National Laboratories, a third generation source of synchrotron radiation. The source provides highly coherent X-ray radiation with high-photon flux (>1012 photons/s) at high-photon energies (5,70 keV). Radiographic and light microscopy images of the gerbil cochlear slice samples were compared. It has been determined that a 20-,m thick tissue slice induces a phase shift between 1/3, and 2/3,. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc. [source] An additional soft X-ray component in the dim low/hard state of black hole binariesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2010C. Y. Chiang ABSTRACT We test the truncated disc models using multiwavelength (optical/ultraviolet/X-ray) data from the 2005 hard state outburst of the black hole Swift J1753.5,0127. This system is both fairly bright and has fairly low interstellar absorption, so gives one of the best data sets to study the weak, cool disc emission in this state. We fit these data using models of an X-ray illuminated disc to constrain the inner disc radius throughout the outburst. Close to the peak, the observed soft X-ray component is consistent with being produced by the inner disc, with its intrinsic emission enhanced in temperature and luminosity by reprocessing of hard X-ray illumination in an overlap region between the disc and corona. This disc emission provides the seed photons for Compton scattering to produce the hard X-ray spectrum, and these hard X-rays also illuminate the outer disc, producing the optical emission by reprocessing. However, the situation is very different as the outburst declines. The optical is probably cyclo-synchrotron radiation, self-generated by the flow, rather than tracing the outer disc. Similarly, limits from reprocessing make it unlikely that the soft X-rays are directly tracing the inner disc radius. Instead they appear to be from a new component. This is seen more clearly in a similarly dim low/hard state spectrum from XTE J1118+480, where the 10 times lower interstellar absorption allows a correspondingly better view of the ultraviolet/extreme ultraviolet (EUV) emission. The very small emitting area implied by the relatively high temperature soft X-ray component is completely inconsistent with the much larger, cooler, ultraviolet component which is well fit by a truncated disc. We speculate on the origin of this component, but its existence as a clearly separate spectral component from the truncated disc in XTE J1118+480 shows that it does not simply trace the inner disc radius, so cannot constrain the truncated disc models. [source] The first broad-band X-ray study of the Supergiant Fast X-ray Transient SAX J1818.6,1703 in outburstMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2009L. Sidoli ABSTRACT The Supergiant Fast X-ray Transient (SFXT) SAX J1818.6,1703 underwent an outburst on 2009 May 6 and was observed with Swift. We report on these observations which, for the first time, allow us to study the broad-band spectrum from soft to hard X-rays of this source. No X-ray spectral information was available on this source before the Swift monitoring. The spectrum can be deconvolved well with models usually adopted to describe the emission from HMXB X-ray pulsars, and is characterized by a very high absorption, a flat power law (photon index ,0.1,0.5) and a cut-off at about 7,12 keV. Alternatively, the SAX J1818.6,1703 emission can be described with a Comptonized emission from a cold and optically thick corona, with an electron temperature kTe= 5,7 keV, a hot seed photon temperature, kT0, of 1.3,1.4 keV and an optical depth for the Comptonizing plasma, ,, of about 10. The 1,100 keV luminosity at the peak of the flare is 3 × 1036 erg s,1 (assuming the optical counterpart distance of 2.5 kpc). These properties of SAX J1818.6,1703 resemble those of the prototype of the SFXT class, XTE J1739,302. The monitoring with Swift/XRT reveals an outburst duration of about 5 d, similar to other members of the class of SFXTs, confirming SAX J1818.6,1703 as a member of this class. [source] The pulsar synchrotron: coherent radio emissionMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2009I. Contopoulos ABSTRACT We propose a simple physical picture for the generation of coherent radio emission in the axisymmetric pulsar magnetosphere that is quite different from the canonical paradigm of radio emission coming from the magnetic polar caps. In this first paper, we consider only the axisymmetric case of an aligned rotator. Our picture capitalizes on an important element of the magnetohydrodynamic (MHD) representation of the magnetosphere, namely the separatrix between the corotating closed-line region (the ,dead zone') and the open-field lines that originate in the polar caps. Along the separatrix flows the return current that corresponds to the main magnetospheric electric current emanating from the polar caps. Across the separatrix, both the toroidal and poloidal components of the magnetic field change discontinuously. The poloidal component discontinuity requires the presence of a significant annular electric current which has up to now been unaccounted for. We estimate the position and thickness of this annular current at the tip of the closed line region, and show that it consists of electrons (positrons) corotating with Lorentz factors on the order of 105, emitting incoherent synchrotron radiation that peaks in the hard X-rays. These particles stay in the region of highest annular current close to the equator for a path-length of the order of 1 m. We propose that, at wavelengths comparable to that path-length, the particles emit coherent radiation, with radiated power proportional to N2, where N is the population of particles in the above path-length. We calculate the total radio power in this wavelength regime and its scaling with pulsar period and stellar magnetic field and show that it is consistent with estimates of radio luminosity based on observations. [source] | |||||||||||||