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Showing papers on "Synchrotron radiation published in 1997"


Journal ArticleDOI
TL;DR: In this paper, the authors observed that the synchrotron power is observed to peak at hard X-ray energies, a behavior never seen before in this or any other blazar.
Abstract: The BL Lac object Mkn 501, one of the only three extragalactic sources (with Mkn 421 and 1ES 2344+514) so far detected at TeV energies, was observed with the BeppoSAX satellite on 7, 11, and 16 April 1997 during a phase of high activity at TeV energies, as monitored with the Whipple, HEGRA and CAT Cherenkov telescopes. Over the whole 0.1-200 keV range the spectrum was exceptionally hard (alpha =< 1, with F_nu ~ nu^{-alpha}) indicating that the X-ray power output peaked at (or above) ~100 keV. This represents a shift of at least two orders of magnitude with respect to previous observations of Mkn 501, a behavior never seen before in this or any other blazar. The overall X-ray spectrum hardens with increasing intensity and, at each epoch, it is softer at larger energies. The correlated variability from soft X-rays to the TeV band points to models in which the same population of relativistic electrons produces the X-ray continuum via synchrotron radiation and the TeV emission by inverse Compton scattering of the synchrotron photons or other seed photons. For the first time in any blazar the synchrotron power is observed to peak at hard X-ray energies. The large shift of the synchrotron peak frequency with respect to previous observations of Mkn 501 implies that intrinsic changes in the relativistic electron spectrum caused the increase in emitted power. Due to the very high electron energies, the inverse Compton process is limited by the Klein-Nishina regime. This implies a quasi-linear (as opposed to quadratic) relation of the variability amplitude in the TeV and hard X-ray ranges (for the SSC model) and an increase of the inverse Compton peak frequency smaller than that of the synchrotron peak frequency.

288 citations


Journal ArticleDOI
TL;DR: In this article, a comparison of the predicted bulk Compton radiation with the observed soft X-ray fluxes was made and it was shown that these jets must be optically very thin, which eliminates the importance of such processes as Coulomb interactions, pair annihilation, and bremsstrahlung and determines the minimum distance from the black hole where a powerful jet can be fully developed.
Abstract: We use multiwavelength spectra of core-dominated flat spectrum radio-loud quasars (FSRQs) to study properties of jets in active galactic nuclei. From a comparison of the predicted bulk Compton radiation with the observed soft X-ray fluxes, we find that these jets must be optically very thin. This eliminates the importance of such processes as Coulomb interactions, pair annihilation, and bremsstrahlung and determines the minimum distance from the black hole where a powerful jet can be fully developed (accelerated, collimated, and mass loaded). In the case of pair dominated jets, this distance is 100GMBH/c2. Further constraints on the parameters of a jet can be derived from luminosities and positions of spectral peaks of low-energy (IR/optical) and high-energy (γ-ray) radiation components, provided that both are produced by the same population of electrons. Whereas there appears to be a consensus about the synchrotron origin of the low-energy component, there is still debate about the mechanism of production of γ-rays. Most likely, they result from Comptonization of a soft radiation field by the same electrons that produce synchrotron radiation. Such a soft radiation field can be provided by the synchrotron process in a jet, by the accretion disk, and by a fraction of the disk radiation that is reprocessed/rescattered by emission line clouds, dust, and intercloud medium. We show that for FSRQs, the production of the high-energy radiation can be dominated by Comptonization of synchrotron radiation only for jets with moderate bulk Lorentz factors Γj (3) or if external radiation fields are much weaker than those observed in typical quasars. Furthermore, in synchrotron self-Compton (SSC) models, the relativistic plasma producing nonthermal radiation is constrained to be very weakly magnetized (B' < 0.01 gauss) and located at very large distances (r ~ 1019 cm). These can impose problems with jet confinement and with short observed timescale of variability. In the external radiation Compton (ERC) models, the magnetic fields are predicted to be much stronger (B' ~ 100 gauss), and nonthermal radiation can be produced very closely to the black hole (r ~ 1016 cm), which alleviates the problems with plasma confinement and short timescale variability. However, because of the close proximity to the black hole, the constraints imposed by the bulk Compton radiation imply that the plasma must be free of e+e- pairs. Finally, we discuss the difficulties that existing models have in explaining the sharp spectral breaks at MeV energies and postulate a "hot electron" version of the ERC scenario for the production of MeV peaks. We show that appropriate electron "temperatures" (kT ~ 100 MeV) to produce the luminosity peak at MeV energies by Comptonization of external UV radiation are achievable at subparsec distances only for proton-electron plasmas.

196 citations


Journal ArticleDOI
TL;DR: The emergence of the synchrotron radiation center in the past decade has resulted in a tremendous development of various techniques as discussed by the authors, and XAS is an efficient tool for describing local organization in ma...
Abstract: The emergence of the synchrotron radiation center in the past decade has resulted in a tremendous development of various techniques. XAS is an efficient tool for describing local organization in ma...

122 citations


Journal ArticleDOI
TL;DR: In this paper, the symmetry of the phases in disordered perovskite has been investigated using X-ray and synchrotron radiation, showing that the compound is a monoclinic ferroelectric at 293 K, undergoes a structural transition to another tetragonal state at about 355 K and finally transforms into a cubic form at approximately 376 K.

111 citations


Journal ArticleDOI
TL;DR: In this paper, the design of a synchrotron x-ray liquid surface spectrometer at beamline X19C at the National Synchoretron Light Source is described.
Abstract: The design of a synchrotron x-ray liquid surface spectrometer at beamline X19C at the National Synchrotron Light Source is described. This spectrometer is capable of performing the full range of x-ray surface scattering techniques. A few examples of measurements made using this spectrometer are presented, including studies of organic monolayers on the surface of water and of the structure of strongly fluctuating oil–microemulsion interfaces. The measurements discussed illustrate the accuracy, resolution, and capabilities of the spectrometer.

109 citations


Journal ArticleDOI
TL;DR: In this article, the authors examined the spectra of 11 gamma-ray bursts obtained by the Large Area Detectors on BATSE and found that all of the observed asymptotic spectral slopes lie in the predicted range.
Abstract: Relativistic shock models of gamma-ray bursts may be tested by comparing their predicted low-energy asymptotic spectral indices s to observations. Synchrotron radiation theory predicts that the instantaneous spectrum has s = 1/3, and the spectrum integrated over the radiative decay of the electrons' energies has s = 1/2 with other cases lying between these limits. We examine the spectra of 11 bursts obtained by the Large Area Detectors on BATSE. One agrees with the predicted instantaneous spectrum, as does the initial portion of a second, and three are close to the predicted integrated spectrum. All of the observed asymptotic spectral slopes lie in the predicted range. This evidence for relativistic shocks is independent of detailed models of bursts and of assumptions about their distances. Radiation observed with the predicted instantaneous spectrum has a comparatively smooth time dependence, consistent with the necessarily long radiation time, while radiation observed with the predicted integrated spectrum has a spiky time dependence, consistent with the necessarily short radiation time.

106 citations


Journal ArticleDOI
TL;DR: The application of synchrotron radiation in the field of radiography is now expanding and it is clear that very substantial improvements in image quality and patient dose can be realized.
Abstract: The use of synchrotron radiation is not widespread in the field of medicine and in fact few health-care professionals have even heard of it. It is the purpose of this article to explain what it is and to give some examples of how it can contribute to medical science. X-rays have been used for diagnostic medical imaging for more than 100 years and, whilst new techniques such as computed tomography have been developed, the means of producing x-rays has altered little during that time. Synchrotron radiation sources provide multiple, extremely intense and tuneable beams of photons over a huge range of energies from infrared through to hard x-rays. Their advent has revolutionized many experimental techniques and synchrotron radiation is being applied across many fields from imaging to molecular dynamics. It has spawned several methods for studying live and wet tissue samples, yielding information on both structure and composition on all length scales down to atomic resolution. Such techniques have played a crucial role in the development of molecular biology and the solution of protein structures. The application of synchrotron radiation in the field of radiography is now expanding and it is clear that very substantial improvements in image quality and patient dose can be realized. Following an overview of the production and properties of synchrotron radiation, some of the ways in which this remarkable tool has already been exploited for medical research are reviewed and some potential clinical opportunities highlighted.

105 citations


Journal ArticleDOI
TL;DR: In this article, the design of a beamline for circularly polarised radiation from an elliptical double undulator to be built at BESSY II has been presented, which can achieve high energy resolution from 6000 to 13 000 at a flux between about 10 10 and 10 12 photon/s, respectively.
Abstract: We present the design of a beamline for circularly polarised radiation from an elliptical double undulator to be built at BESSY II. The UE56 undulator of Sasaki type will emit simultaneously two angularly separated circularly polarised beams of opposite helicities. The undulator will, through emissions in first, third and fifth harmonics, provide circularly polarised radiation in the energy range 89–1328 eV. The beamline essentially consists of a plane grating monochromator (PGM) working with collimated light and employing only one set of optical elements for steering and monochromatising the two beams. A high energy resolution from 6000 to 13 000 can be achieved at a flux between about 10 10 and 10 12 photon/s, respectively. The helicity of circular polarisation can be switched dynamically in the beamline at a high rate (>100 Hz) by use of a suitable chopper. The degree of circular polarisation of the source ranging from 78 to 100% is well preserved by the beamline. In the worst case — at the lowest energy — the degree of polarisation is reduced by 5%. In the higher energy range above 357 eV the input degree of circular polarisation can even be increased by the beamline.

99 citations


Journal ArticleDOI
TL;DR: In this paper, a combination of elemental selectivity and magnetic sensitivity is achieved by using circularly polarized soft X-rays and exploiting the effect of magnetic circular dichroism, which obtains information about the magnetic state of individual chemical components within the sample.

97 citations


Journal ArticleDOI
TL;DR: The accuracy of detector calibration in the UV, vacuum-ultraviolet, and soft-x-ray spectral ranges could be significantly improved by the use of the synchrotron radiation electrical substitution radiometer (SYRES) as the primary detector standard.
Abstract: The accuracy of detector calibration in the UV, vacuum-ultraviolet, and soft-x-ray spectral ranges could be significantly improved by the use of the synchrotron radiation electrical substitution radiometer (SYRES) as the primary detector standard. The SYRES radiometer is optimized for use with spectrally dispersed synchrotron radiation as supplied by two monochromator beam lines in the radiometry laboratory of the Physikalisch-Technische Bundesanstalt at the Berlin electron-storage ring (BESSY). Wavelength ranges from 0.8 to 25 nm and from 35 to 400 nm are covered. The typically available radiant power of approximately 1-10 microW can be measured with the SYRES radiometer with a standard relative uncertainty of less than 0.2%. The spectral responsivity of qualified photodiodes for use as secondary detector standards is determined by direct comparison with the primary detector standard at an arbitrary wavelength. At present, the scale of spectral responsivity is realized with a standard relative uncertainty of well below 1% in the spectral ranges 0.8-3.5 nm, 5-25 nm, and 120-400 nm. We provide a comprehensive description of the SYRES radiometer and of the two facilities for detector calibration in the UV and vacuum-ultraviolet spectral ranges and in the soft-x-ray spectral range, respectively, and we discuss the achievable uncertainties in the calibration of detectors.

92 citations


Journal ArticleDOI
TL;DR: Vacuum ultraviolet radiation was generated from an undulator at the Advanced Light Source Synchrotron facility and used for photoionization detection of reaction products in a new universal crossed molecular beams machine.
Abstract: Vacuum ultraviolet radiation was generated from an undulator at the Advanced Light Source Synchrotron facility and used for photoionization detection of reaction products in a new universal crossed molecular beams machine. A description of the machine and its performance is presented. Initial experiments on the photodissociation of methylamine (CH3 NH2), ozone (O3), oxalyl chloride [ (OCCl)2] as well as the reactive scattering of Cl with C3 H8 show many of the advantages of photoionization in comparison to electron impact ionization, which has been exclusively used in such instruments in the past. “Momentum matching” of reaction products is much more easily accomplished than in electron impact studies due to suppression of dissociative ionization. The tunability of the vacuum ultraviolet radiation can be used to suppress background from residual gases especially when it is desired to detect free radical reaction products. Even when the tunability cannot be used to suppress background, the fact that little...

Journal ArticleDOI
TL;DR: In this article, the authors review the time structure of synchrotron radiation and its use for fast time-resolved diffraction experiments in macromolecular photocycles using flash photolysis.
Abstract: We review the time structure of synchrotron radiation and its use for fast time-resolved diffraction experiments in macromolecular photocycles using flash photolysis to initiate the reaction. The source parameters and optics for ID09 at ESRF are presented together with the phase-locked chopper and femtosecond laser. The chopper can set up a 900 Hz pulse train of 100 ps pulses from the hybrid bunch-mode and, in conjunction with a femtosecond laser, it can be used for stroboscopic data collection with both monochromatic and polychromatic beams. Single-pulse Laue data from cutinase, a 22 kD lipolic enzyme, are presented which show that the quality of single-pulse Laue patterns are sufficient to refine the excited state(s) in a reaction pathway from a known ground state. The flash photolysis technique is discussed and an example is given for heme proteins. The radiation damage from a laser pulse in the femto and picosecond range can be reduced by triggering at a wavelength where the interaction is strong. We propose the use of microcrystals in the range 25–50 μm for efficient photolysis with femto and picosecond pulses. The performance of circular storage rings is compared with the predicted performance of an X-ray free electron laser (XFEL). The combination of micro beams, a gain of 105 photons per pulse and an ultrashort pulse length of 100 fs is likely to improve pulsed diffraction data very substantially. It may be used to image coherent nuclear motion at atomic resolution in ultrafast uni-molecular reactions.

Proceedings ArticleDOI
01 Nov 1997
TL;DR: In this paper, an x-ray long trace profiler (XLTP) was proposed to measure surface slope errors with precision and accuracy better than 25 nrad (rms) and 50 nrad(mis), respectively, with alateral resolution of 5 mm in the meridional and less than I mm in a sagittal direction.
Abstract: In this paper we describe an x-ray long trace profiler (XLTP) that takes an x-ray synchrotron beam as a wavefrontreference. According to results of experiments conducted on the Optics Beamline at the ESRF, this instrument allows us tomeasure surface slope errors with precision and accuracy better than 25 nrad (rms) and 50 nrad (mis), respectively, with alateral resolution of 5 mm in the meridional and less than I mm in the sagittal direction.A very similar technique was developed to figure in situ mirrors mounted on mechanical benders into a stigmatic shape formicrofocusing purposes. Micron spot sizes were achieved without difficulty and submicron precision should be possible.The technique is particularly useful if energy tunability is needed. The emphasis has been put on automation and speed ofthe measurement.Keywords: Surface metrology, x-ray mirrors, active optics, microfocusing, synchrotron radiation, multilayers. 1. INTRODUCTION In the light of recent experiments using coherence it became evident that x-ray mirrors for synchrotron radiation are still notgood enough"2. The quality of mirrors and of multilayer substrates must be extremely high to preserve the coherence ofthird generation synchrotron sources. This also applies to focusing and spherical waves. For example, in microdiffractionexperiments applied, e.g., to high pressure studies, the microimage of the source, regarding both the small size and thepurity, should not be degraded by the focusing optics. Whereas highly perfect single crystals do not affect coherence, theslope errors of the best presently available mirrors and multilayer imperfections have shown to deteriorate the phasecontrast significantly. In the following we will briefly recall what are the requirements for mirror quality.A height error Lz of a surface reflecting x-rays at a grazing angle generates a peak-to-valley (PV) phase distortion Ltp

Journal ArticleDOI
TL;DR: In this paper, it was shown that wide-angle X-ray scattering patterns can be obtained from single polymeric fibers with a 2 μm synchrotron radiation beam in a few seconds per pattern.
Abstract: It is shown that wide-angle X-ray scattering patterns can be obtained from single polymeric fibers with a 2 μm synchrotron radiation beam in a few seconds per pattern. Preferred orientation was obs...

Journal ArticleDOI
TL;DR: In this article, the authors examined the spectra of 11 gamma-ray bursts obtained by the Large Area Detectors on BATSE and found that all the observed asymptotic spectral slopes lie in the predicted range.
Abstract: Relativistic shock models of gamma-ray bursts may be tested by comparison of their predicted low energy asymptotic spectral indices s to observations. Synchrotron radiation theory predicts that the instantaneous spectrum has s = - 1/3 and the spectrum integrated over the radiative decay of the electrons' energies has s = 1/2, with other cases lying between these limits. We examine the spectra of 11 bursts obtained by the Large Area Detectors on BATSE. One agrees with the predicted instantaneous spectrum, as does the initial portion of a second, and three are close to the predicted integrated spectrum. All the observed asymptotic spectral slopes lie in the predicted range. This evidence for relativistic shocks is independent of detailed models of bursts and of assumptions about their distances. Radiation observed with the predicted instantaneous spectrum has a comparatively smooth time dependence, consistent with the necessarily long radiation time, while that with the predicted integrated spectrum has a spiky time dependence, consistent with the necessarily short radiation time.

Journal ArticleDOI
TL;DR: In this paper, a detailed photon energy-dependent and angle-dependent SRXPS study was performed in the 120 ÷ 175 eV photon energy range and the compatibility of the experimental findings with models of the current literature was examined.
Abstract: Synchrotron radiation X-ray photoemission spectroscopy (SRXPS), used with an optimized surface and interface sensitivity, is a unique tool to determine the chemical composition and spatial extension of the suboxide layer present at the Si/SiO2 interface. The bonding at ‘thermal interfaces’ appear to be essentially dependent on the Si crystal orientation. For Si(001)/SiO2 a detailed photon energy-dependent and angle-dependent. SRXPS study (in the 120 ÷ 175 eV photon energy range) has been performed. Previous results on higher-oxidation states cross-section resonances around hv = 130 eV are re-examined. The various oxide states do not present photoelectron diffraction peaks, when polar scans are performed in the (110) azimuthal plane. On the other hand, there is evidence that substrate silicon atoms close to the interface retain orientational order. Limits in the vertical distribution of the suboxides are given. The compatibility of our experimental findings with models of the current literature — in particular the so-called ‘dimerized interface’ model — is examined.

Journal ArticleDOI
TL;DR: In this article, the authors examined four electron-dominated flares, two from the GRS instrument on 1989 March 6, and two from EGRET and BATSE instruments on 1991 June 30 and 1991 July 2.
Abstract: We examine four electron-dominated flares, two from the GRS instrument on 1989 March 6, and two from the EGRET and BATSE instruments on 1991 June 30 and 1991 July 2. Their photon spectra, which are almost all caused by electron bremsstrahlung radiation, show significant deviations from a simple power-law form. These are attributed to the deviations in the spectra of the accelerated electrons. We develop three stochastic acceleration models to explain the shape of the photon spectra: the hard sphere model, the whistler wave model, and a more general, but still simplified, stochastic acceleration model. For photon emissions, we use a simple sum of the thin target emission from the trapped electrons at the acceleration site near the loop top and the thick target emission from the escaping electrons which travel along the magnetic field lines and radiate in the denser chromosphere at the footpoints. We find that the hard sphere model does not fit any of the flares and can be ruled out. The other two models show that the high-energy cutoff in the two GRS flares can be attributed to synchrotron radiation losses in the presence of a 500 G magnetic field at the acceleration site. The observed break in the photon spectra of all four flares around 1 MeV is attributed to a combination of the energy dependence of the escape time of particles out of the acceleration region and the change in the energy dependence of the bremsstrahlung cross section between the nonrelativistic and relativistic regimes. Further steepening of the spectrum at even lower energies is caused by Coulomb losses at the acceleration site. We find that acceleration timescales as low as ~1 s are possible with a ratio of turbulent to the magnetic field energy densities of ~10-4. We also set limits on the plasma density, the size of the acceleration region, and the spectrum of the plasma turbulence.

Journal ArticleDOI
TL;DR: In this article, a steradiancy-type zero kinetic energy photoelectron (ZEKE-PE) analyzer and the high resolution monochromatized vacuum ultraviolet (VUV) undulator synchrotron radiation of the chemical dynamics beamline at the advanced light source (ALS) were used to filter prompt electrons and by employing a proper voltage pulsing scheme adapted to the timing structure of the ALS, they achieved a resolution of 0.5 meV (FWHM).
Abstract: We have demonstrated a resolution of 0.8 meV [full width at half-maximum (FWHM)] for threshold photoelectron measurements using a steradiancy-type zero kinetic energy photoelectron (ZEKE-PE) analyzer and the high resolution monochromatized vacuum ultraviolet (VUV) undulator synchrotron radiation of the chemical dynamics beamline at the advanced light source (ALS). Using this high resolution ZEKE-PE energy analyzer to filter prompt electrons and by employing a proper voltage pulsing scheme adapted to the timing structure of the ALS, we have achieved a resolution of 0.5 meV (FWHM) for pulsed field ionization photoelectron (PFI-PE) measurements with little contamination from prompt photoelectrons produced from direct photoionization and autoionizing processes. The experiment scheme presented here is generally applicable to PFI-PE studies using multi-bunch VUV synchrotron radiation at other synchrotron radiation facilities.

Journal ArticleDOI
TL;DR: In this paper, an undulator-based synchrotron source and a tunable x-ray monochromator were used to produce a beam with a flux of 4×108 photons in an energy bandwidth of 920±110μeV (ΔE/E≈6.2×10−8) at a photon energy of 14.4 keV.
Abstract: With an undulator-based synchrotron source and a tunable x-ray monochromator, we produce an x-ray beam with a flux of 4×108 photons/s in an energy bandwidth of 920±110 μeV (ΔE/E≈6.2×10−8) at a photon energy of 14.4 keV. The tunability of the monochromator allows for a measurement of lattice excitations in α-Fe using the technique of inelastic nuclear resonant scattering from 57Fe. The phonon density-of-states are extracted from the measurement and compared to the calculated phonon density-of-states derived from neutron-scattering measurements.

Journal ArticleDOI
TL;DR: An apparatus for measuring time-dependent x-ray diffraction is demonstrated, which measures the duration of 5-keV pulses from the Advanced Light Source synchrotron to be 70ps and in the averaging mode, trigger jitter results in 2-ps temporal resolution.
Abstract: We demonstrate an apparatus for measuring time-dependent x-ray diffraction. X-ray pulses from a synchrotron are diffracted by a pair of Si(111) crystals and detected with an x-ray streak camera that has single-shot resolution of better than 1 ps. The streak camera is driven by a photoconductive su itch, which is triggered by 100-fs laser pulses at a repetition rate of 1 kHz. The laser and the streak camera are synchronized with the synchrotron pulses. In the averaging mode, trigger jitter results in 2-ps temporal resolution. We measured the duration of 5-keV pulses from the Advanced Light Source synchrotron to be 70 ps. (C) 1997 Optical Society of America.


Journal ArticleDOI
TL;DR: In this paper, a time resolved core level spectroscopy study was performed on photoexcited Si(111)2×1 surfaces with subnanosecond resolution, which enabled measuring band bending fluctuations, caused by surface carrier dynamics, during the first nanosecond after photoexcitation; differences in the Si2p core level lineshape, dependent on the pumpprobe time delay, were also observed.
Abstract: Combining the use of a UV storage ring free electron laser and of synchrotron radiation, a time resolved core level spectroscopy study has been performed on photoexcited Si(111)2×1 surfaces with subnanosecond resolution. This enabled us to measure band bending fluctuations, caused by surface carrier dynamics, during the first nanosecond after photoexcitation; differences in the Si2p core level lineshape, dependent on the pump-probe time delay, were also observed. The presence of defects was found to reduce the fluctuations and make the carrier recombination process faster.

Journal ArticleDOI
TL;DR: The increasing availability of synchrotron x-ray sources has stimulated the development of advanced hard X-ray (E⩾5 keV) microprobes.
Abstract: The increasing availability of synchrotron x-ray sources has stimulated the development of advanced hard x-ray (E⩾5 keV) microprobes. It is now possible to achieve intense submicron x-ray beams with a variety of techniques including Fresnel zone plates, Kirkpatrick–Baez mirrors, tapered capillaries and Bragg–Fresnel optics. These synchrotron-based x-ray microprobes can be used for ultra-sensitive elemental detection by x-ray fluorescence/absorption and for microdiffraction to identify phase and strain with submicron resolution. Advanced methods for forming microbeams are reviewed and the relative merits of each approach are discussed. The efficient techniques developed for synchrotron beams can also be used to tailor the beam properties from conventional x-ray sources. © 1997 This article is a US Government work and, as such, is in the public domain in the United States of America

Journal ArticleDOI
TL;DR: In this paper, an evacuated, temperature-controlled cell has been built for use on the small-angle X-ray scattering instrument D24 at the synchrotron radiation facility LURE.
Abstract: An evacuated, temperature-controlled cell has been built for use on the small-angle X-ray scattering instrument D24 at the synchrotron radiation facility LURE. The sample is placed in a quartz capillary sealed in a stainless-steel holder using a vacuum-tight glue. Several O rings provide a vacuum path upstream and downstream from the cell, so that the X-ray beam only meets the capillary walls and the solution under study between the slits and the beam stop, while the sample is maintained under atmospheric pressure. The cell temperature is controlled via a water circulation through a copper sheath in tight contact with the steel holder. The use of this cell results in a marked reduction of the background, as observed in two series of parallel experiments using a conventional cell and this evacuated cell. The decrease ranges from a factor of 2 at s 1 values larger than 0.008 A−1 to more than 15 at s = 0.00116 A−1, where s is the modulus of the scattering vector (s = 2sin θ/λ, 2θ is the scattering angle and λ is the wavelength of the X-rays).

Journal ArticleDOI
TL;DR: In this article, a computer program was developed to investigate the significance of various physical effects to the dose distribution in the resist material, which in turn determined the lateral structure resolution and the quality of the resist structures.
Abstract: Deep x-ray lithography with synchrotron radiation is the key microfabrication process in the LIGA technology. Micro-components with a height of some up to several mm can be manufactured with sub- precision. The pattern transfer accuracy is governed by technological constraints like thermal deformation of the mask as well as by various physical effects, e.g. diffraction, emission of photo- and Auger electrons, fluorescence radiation, radiation scattering and divergence of the synchrotron radiation beam. A computer program has been developed to investigate the significance of these effects to the dose distribution in the resist material, which in turn determines the lateral structure resolution and the quality of the resist structures. In this paper the models used for the calculation and the calculation procedure are introduced and the weight of the different contributions with respect to transfer accuracy is investigated. It is shown that beam divergence and diffraction are much less important than the image blur caused by photoelectrons. Fluorescence radiation emitted from the mask membrane or the substrate contributes to the dose deposition in the resist if mask membrane or substrate consists of high-atomic-number material. Scattering of radiation is negligible for resist layers which are less than some mm thick. The calculations are compared with measurement results for different substrate materials, synchrotron radiation sources and resist heights. A good agreement was found between calculated dose distributions and measured resist side wall profiles. This allows a partial compensation of the above-mentioned accuracy limiting effects early in the mask design phase.


Journal ArticleDOI
TL;DR: The layered manganite La 1.2Sr1.8Mn2O7 is important in that it displays giant negative magnetoresistance properties, and its study complements the growing body of what we know about the complex size.
Abstract: The layered manganite La1.2Sr1.8Mn2O7 is important in that it displays giant negative magnetoresistance properties, and its study complements the growing body of what we know about the complex size...

Journal ArticleDOI
TL;DR: In this paper, it was shown that the total and partial photoionization cross sections of those clusters oscillate on a scale of energy typically reached by synchrotron radiation, and the frequencies of the oscillations are linked to geometrical properties of the electron cloud, such as its thickness and the diameter of the cluster.

Journal ArticleDOI
TL;DR: In this paper, the maximum ratio of TeV gamma-ray luminosity to X-ray during flaring that is allowed by the homogeneous synchrotron self-Compton model for the case of no significant photon-photon absorption in the source was determined.
Abstract: Based on the detected variability time-scales of X-ray and Te V gamma-ray emission, and the observed multiwavelength photon spectrum, of Mrk 421 we place constraints on the allowed parameter space (magnetic field and Doppler factor of the emission region) for the homogeneous synchrotron self-Compton model. The spectra calculated for the allowed parameters are marginally consistent with the available spectral information above '" 1 Te V reported by the Whipple Observatory in the case of a 1-d flare time-scale. However, for the recently reported very short duration flares varying on a time-scale of 15 min, the calculated spectra are significantly steeper, suggesting that the homogeneous synchrotron self-Compton model has problems in describing the relatively flat observed spectra extending above a few TeV. We determine the maximum ratio of TeV gamma-ray luminosity to X-ray luminosity during flaring that is allowed by the homogeneous synchrotron self-Compton model for the case of no significant photon-photon absorption in the source.

Book
22 May 1997
TL;DR: In this article, the authors provide a sound and convenient basis for designing beamlines for monochromatic soft x-ray radiation, which can also be used to help ensure that beamlines being built are optimized for the experiments to be performed on them.
Abstract: Intended to provide scientists and engineers at synchrotron radiation facilities with a sound and convenient basis for designing beamlines for monochromatic soft x-ray radiation, this text will also be helpful to the users of synchrotron radiation who want to help ensure that beamlines being built are optimized for the experiments to be performed on them. The primary purpose of a beamline is to capture as much of the light of the source as possible and then to transfer the desired portion of that light as completely as possible to the experiment. With the development of dedicated, brilliant synchrotron radiation sources, the first half of the task has been greatly simplified. The beamline designer must contend with the second half of the problem -- conserving the brilliance of the source through an optical system which monochromatizes and focuses the radiation.