Showing papers on "Synchrotron radiation published in 1984"
TL;DR: In this paper, the properties of the synchrotron continuum were calculated on the basis of a steady spherically symmetric MHD model of the flow in the Crab nebula.
Abstract: The properties of the synchrotron continuum are calculated on the basis of a steady spherically symmetric MHD model of the flow in the Crab nebula. The model accounts for the spectral distribution of the continuum from the optical to gamma-rays, and semiquantitatively for its observed spatial distribution. The model does not account for the radio portion of the Crab nebula's spectrum.
582 citations
TL;DR: In this article, high resolution Si 2p photoelectron spectra obtained with synchrotron radiation were used to determine the distribution of oxidation states in the intermediary layer at the SiO2Si interface.
Abstract: High resolution Si 2p photoelectron spectra obtained with synchrotron radiation are used to determine the distribution of oxidation states in the intermediary layer at the SiO2‐Si interface. A ratio of 0.4:0.3:0.3 is found for the Si3+:Si2+:Si1+ intensities independent of Si surface orientation and oxide thickness. The interface is not completely abrupt (5±1 A width).
376 citations
01 Oct 1984-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, a simple beam line is suggested which would allow a substantial increase in low energy X-ray flux (measurements down to Al and Si) with the sample and detector in a He atmosphere.
Abstract: The problem of absorption of soft X-rays by thick Be windows in hard X-ray beam lines is well known. Although the signal at 2.4 keV was reduced by ∼ 103 we have routinely measured the absorption spectra of S (2472 eV) and elements at higher energies including Cl, Ar and K. These spectra were obtained on hard X-ray beam lines at Stanford Synchrotron Radiation Laboratory (SSRL) with Si(111) monochromator crystals and a fluorescent ion chamber detector [1]. Higher energy harmonics were minimized by detuning and the end station was enclosed in a helium bag to prevent absorption by air. Although the diminished X-ray flux and decreasing fluorescent yield were serious negative factors at these low X-ray energies the spectra from thick samples were of excellent quality with sufficient sensitivity to characterize 1% S in coal. Representative spectra are shown comparing data from focused and unfocused beam lines and with S data from JUMBO [2]. Comparison of Ar and KCl data to excellent data found in the older literature [3–5] allow a confirmation of the resolution function (energy bandpass) of the monochromator. A simple new beam line is suggested which would allow a substantial increase in low energy X-ray flux (measurements down to Al and Si) with the sample and detector in a He atmosphere.
291 citations
TL;DR: The Laue technique offers advantages for the recording of diffraction patterns from short-lived structural intermediates; that is, for time-resolved crystallography.
Abstract: In conventional x-ray diffraction experiments on single crystals, essentially monochromatic x-rays are used. If polychromatic x-rays derived from a synchrotron radiation spectrum are used, they generate a Laue diffraction pattern. Laue patterns from single crystals of macromolecules can be obtained in less-than 1 second, and significant radiation damage does not occur over the course of an exposure. Integrated intensities are obtained without rotation of the crystal, and individual structure factors may be extracted for most reflections. The Laue technique thus offers advantages for the recording of diffraction patterns from short-lived structural intermediates; that is, for time-resolved crystallography.
124 citations
TL;DR: The use of synchrotron X-radiation (SR) in protein crystallography is discussed in this paper, with a brief discussion of the basics of protein structure analysis including an outline of the problems of sample radiation damage, the inherent weakness of individual reflections and the large amounts of data that need to be collected as well as the phase problem.
Abstract: This review describes the utilisation of synchrotron X-radiation (SR) in protein crystallography. For the general reader a brief discussion is given of the basics of protein structure analysis including an outline of the problems of sample radiation damage, the inherent weakness of individual reflections and the large amounts of data that need to be collected as well as the 'phase problem' of crystallography. The properties of synchrotron radiation emitted by relativistic electrons in simple circular orbits in bending magnets and by more sophisticated electron motions induced in wiggler or undulator magnets are discussed. The impact of newer high brightness synchrotron radiation sources in protein crystallography is assessed. The instrumentation required to monochromatise and focus the radiation onto typically small protein crystal samples and to detect the diffraction pattern is described. Both step scanning and energy dispersive techniques to optimise anomalous dispersion are covered. A gazetteer is given of the instruments providing data collection facilities for protein crystallography which are available on SR sources around the world. The modifications that are needed to standard data processing techniques are dealt with, taking account, for instance, of the position, angle and wavelength correlatable properties of photons incident to a sample from an SR source; properties which affect reflection prediction in both camera or diffractometer work.
113 citations
TL;DR: In this article, the construction and operation of a cross-correlation phase and modulation fluorometer using the synchrotron radiation facility at the ADONE-Frascati electron storage ring is described.
Abstract: The construction and operation of a cross‐correlation phase and modulation fluorometer using the synchrotron radiation facility at the ADONE–Frascati electron storage ring is described. In the frequency domain the high repetition rate pulsed source gives a large series of equally spaced harmonic frequencies. Use of cross‐correlation techniques in conjunction with such a light source permits one to isolate one harmonic frequency from the adjacent frequencies with high precision. The cross‐correlation frequency required for the analysis of the phase delay and modulation ratio is obtained using two coupled frequency synthesizers, one of which drives the radio‐frequency cavity of the storage ring and the other which modulates the response of the photomultipliers used for the signal detection. The accuracy, reproducibility, and sensitivity of the instrumentation have been determined on a number of systems and are reported.
108 citations
TL;DR: In this article, a device that can produce synchrotron radiation whose polarization can be arbitrary and adjustable is proposed, which can be linear and be switched between two mutually perpendicular directions, or it can be circular and switch between right and left circular polarizations.
103 citations
TL;DR: An angle-, energy-, and spin-resolved photoemission experiment has been performed for Pt(111) with the circularly polarized synchrotron radiation of the new German dedicated storage ring BESSY.
Abstract: An angle-, energy-, and spin-resolved photoemission experiment has been performed for Pt(111) with the circularly polarized synchrotron radiation of the new German dedicated storage ring BESSY. The photoelectron polarization measured as function of the kinetic energy at different photon energies between 6.5 and 24 eV for normal incidence and normal emission shows a pronounced spectral variation up to \ifmmode\pm\else\textpm\fi{}55%. The electron intensities and polarizations observed allow a symmetry-resolved band characterization of Pt in the $\ensuremath{\Gamma}\ensuremath{-}L$ direction.
94 citations
TL;DR: In this article, the power radiation pattern of Smith-Purcell radiation is measured at various latitudes and azimuth angles relative to the electron beam, and the experimental data are used to evaluate the various models and the physical mechanisms previously suggested to describe Smith-purcell radiation.
Abstract: The power radiation pattern of Smith–Purcell radiation is measured at various latitudes and azimuth angles relative to the electron beam. The experimental data are used to evaluate the various models and the physical mechanisms previously suggested to describe Smith–Purcell radiation. Good agreement is observed between the experimental data and the theoretical curves derived from Van den Berg’s analysis [ J. Opt. Soc. Am.63, 1588 ( 1973)]. The radiation mechanism proposed by Salisbury [ J. Opt. Soc. Am.60, 1279 ( 1970)] was analyzed and shown to be too small to account for the measured radiation. The experiment and Van den Berg’s theory predict stronger emission at azimuthal angles off the plane perpendicular to the gratings. This observation leads to conclusions regarding the design of optical cavities for Smith–Purcell free-electron lasers and orotron millimeter-wavelength-radiation tube devices.
91 citations
TL;DR: In this article, a detailed analytical approach to the understanding of the maser synchrotron instability is proposed and the complete dispersion relation is derived in a situation where the cold plasma density is small.
Abstract: It has recently been shown that radio emission from the Earth, the so‐called auroral kilometric radiation, is emitted inside cold plasma depleted regions These observations have motivated a new interest in direct generation processes Since it allows the generation of an X mode just above the cutoff frequency of this mode (in agreement with observations) the maser synchrotron instability is a promising candidate A detailed analytical approach to the understanding of this instability is proposed The complete dispersion relation is derived in a situation where the cold plasma density is small (ec=ω2pe/ω2c≪1) The physical significance of this instability is discussed; in particular, the difference between the maser synchrotron instability and the classical Weibel instability is stressed Depending upon the ratio between ‘‘cold’’ and energetic electron components, two regimes, the ‘‘kinetic’’ and the monoenergetic ‘‘ring‐like’’ distribution, are considered and the results are compared with the numerical s
86 citations
TL;DR: In this article, the total absolute cross sections for charge transfer between N2+ ions and Ar have been measured at 8, 14 and 20 eV center of mass translational energy.
TL;DR: An analog feedback control system for instruments which use synchrotron X-radiation and double cyrstal arrangements in a parallel setting as monochromator or plane wave generators is described in this article.
CERN1
TL;DR: In this paper, a balance between these two aspects of the same phenomenon is found to determine the degree of beam polarization that can be built up and maintained in a machine. But the balance between the two aspects is not the same as in this paper.
TL;DR: Azimuthal and polar angular dependent surface extended X-ray absorption fine structure (SEXAFS) studies have been performed on Ag(110)-O(2 × 1) using the synchrotron radiation of the new electron storage ring BESSY.
TL;DR: In this article, the imaginary part of the atomic scattering factor was determined using the optical theorem and the real part f′ computed by the Kramers-Kronig dispersion relation.
Abstract: X-ray absorption spectra about the K edges of Ni, Cu and Ti have been measured at the Stanford Synchrotron Radiation Laboratory. The imaginary part of the atomic scattering factor f′′ was determined using the optical theorem and the real part f′ computed by the Kramers–Kronig dispersion relation. Methods for evaluating this integral as well as the effects on f′ of various experimental errors are investigated. The f′ results for Cu and Ni are compared to data from interferometry experiments.
01 Apr 1984-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, relative detection limits derived from these X-ray spectra were calculated to compare the different excitation modes, showing that XRF shows the highest detection limits, while protons and synchrotron radiation monochromated to 16.5 keV are comparable.
Abstract: Monochromated synchrotron radiation (SXRF), 17.5 keV photons from an X-ray tube (XRF) with Mo anode and 3 MeV protons (PIXE) were used to excite X-ray spectra from thin samples of standard reference materials. Relative detection limits derived from these X-ray spectra were calculated to compare the different excitation modes. XRF shows the highest detection limits, while protons and synchrotron radiation monochromated to 16.5 keV are comparable. Much lower detection limits (down to 0.1 ppm) are experimentally shown with synchrotron radiation monochromated to 9.1 keV. Results are in agreement with theoretical predictions. The advantage of the polarization of the synchrotron radiation has been discussed theoretically and shown experimentally.
TL;DR: In this article, a parametric study of the instability conditions for a supraluminous X mode wave is conducted, and the role played by θ, the propagation angle eb, the normalized density of energetic electrons δ, the energy width of the part of the distribution function where an inversion of population (∂f/∂υ⊥ > 0) occurs, and finally u, the parallel velocity which characterizes the maximum of ∆/∆ φ integrated along a resonance circle.
Abstract: Recent observations at low altitudes made in the source region of the auroral kilometric radiation (AKR hereinafter) strongly support the maser synchrotron instability (MSI) as the relevant generation process for the AKR. This was first realized by Wu and Lee (1979). In a recent work (Le Queau et al. (1984), hereinafter called reference 1) we have proposed an analytical treatment of the MSI. The present work is a continuation of this analytical study. First we investigate the physical process of the MSI, and simple analytical expressions, valid for any distribution functions of nonthermal electrons are given. It is shown that supraluminous X mode waves (ω/k∥c ≫ 1) can resonate with relatively low energy electrons provided that the cold plasma parameter, ec = ωpc²/ωc², is much smaller than unity. The proper frame of reference for studying the resonant coupling between the X mode and nonthermal electrons moves at a parallel velocity k∥c²/ω. Resonance curves are then circles centered around this value and electrons diffuse with almost constant parallel velocities. The difference between the MSI and the standard cyclotron theory (where resonance curves are straight lines while diffusion curves are circles centered around ω/k∥) is stressed. A parametric study of the instability conditions for such a supraluminous wave is conducted. We investigate the role played by θ, the propagation angle eb, the normalized density of energetic electrons δ, the energy width of the part of the distribution function where an inversion of population (∂f/∂υ⊥ > 0) occurs, and finally u, the parallel velocity which characterizes the maximum of ∂f/∂υ⊥ integrated along a resonance circle. In the case of the shifted loss cone distribution used here, u is simply its parallel bulk velocity. Largest growth rates are obtained for k∥c²/ω = u.
TL;DR: In this paper, the use of synchrotron radiation for X-ray standing wave measurements was demonstrated and the case of Br chemisorbed on Si(111) was analyzed with two reflection orders (220 and 440) which showed that lattice relaxation around the As atom can be measured.
TL;DR: In this article, the authors consider relativistic particle acceleration by resonant Alfven waves which are driven internally in a radio source from fully developed fluid turbulence and find that self-similar behavior as described by Lacombe, f(p)proportionalp/sup -//sup s/ but with sroughly-equal4.5, arises self-consistently when this turbulent wave driving coexists with synchrotron losses.
Abstract: We consider relativistic particle acceleration by resonant Alfven waves which are driven internally in a radio source from fully developed fluid turbulence. We find that self-similar behavior as described by Lacombe, f(p)proportionalp/sup -//sup s/ but with sroughly-equal4.5, arises self-consistently when this turbulent wave driving coexists with synchrotron losses. The coupling of the wave and particle distributions provides feedback which drives an arbitrary initial distribution to the form-stable, self-similar form. The model predicts that turbulent plasma in a radio source should evolve toward a synchrotron spectral index, 0.5< or approx. =..cap alpha..< or approx. =1.0 in one particle lifetime, and that the average spectrum of most sources should also be in this range. The theory may also be applicable to other turbulent sites, such as cosmic-ray reaccelertion in the interstellar medium.
01 Jun 1984
TL;DR: In this article, a review of the results concerning more specifically mineralogical systems: X-ray absorption spectroscopy concerning high-resolution edge spectra and Extended Xray absorption fine structure (EXAFS).
Abstract: Synchrotron radiation offers several advantages over the conventional X-ray sources, among which the most important are its high intensity, broad spectral range and natural collimation. Among the numerous techniques which have been recently developed we present a review of the results concerning more specifically mineralogical systems: X-ray absorption spectroscopy concerning high-resolution edge spectra and Extended X-ray absorption fine structure (EXAFS), X-ray diffraction under high P-high T conditions, small-angle scattering, X-ray microanalysis and X-ray topography. For each technique the basic principles are described together with the experimental devices used, before mineralogical examples are given. Two main applications may be pointed out: chemical and structural characterization of disordered systems and kinetic studies (phase transitions and evolution). Many other techniques (photoelectron spectroscopy, X-ray fluorescence analysis ...) which are actually under development as a result of the rapid increase of the use of storage rings are not covered in the present review but will possibly also be used in the near future in Earth Sciences.
TL;DR: In this article, the authors derived volumes and luminosities for several components of the supernova remnant MSH 15 - 52 with the use of measured spectra and a model, and showed that they are probably similar in nature, with the high brightness and unique appearance of the Crab synchrotron nebula being due to the high energy output of the pulsar and the relatively small volume of the confining filaments.
Abstract: With the use of measured spectra and a model, volumes and luminosities are derived for several components of the supernova remnant MSH 15 - 52. The hard, featureless spectrum and spatial symmetry of the X-ray nebula surrounding the central pulsar strongly indicate synchrotron radiation as the source of emission. Power requirements are easily supplied by the pulsar. The observed surface brightness is only 0.00002 that of the X-ray synchrotron emission around the Crab pulsar, and the X-ray luminosity is 0.01 that of the Crab. In spite of the great difference in luminosity and size, the two systems are probably similar in nature, with the high brightness and unique appearance of the Crab synchrotron nebula being due to the high energy output of the pulsar and the relatively small volume of the confining filaments.
TL;DR: In this paper, the effects of the synchrotron emitting relativistic electrons on the emission line regions which characterize active nuclei are discussed, and detailed models of both the inner, dense, broad line and the outer, lower density, narrow line regions are presented, together with the first models of the optically emitting gas often found within extended radio lobes.
Abstract: The effects that the synchrotron emitting relativistic electrons could have on the emission line regions which characterize active nuclei are discussed. Detailed models of both the inner, dense, broad line region and the outer, lower density, narrow line region are presented, together with the first models of the optically emitting gas often found within extended radio lobes. If the relativistic gas which produces the synchrotron radio emission is mixed with the emission line region gas then significant changes in the emission line spectrum will result. The effects of the synchrotron emitting electrons on filaments in the Crab Nebula are discussed in an appendix, along with a comparison between the experimental calculations, which employ the mean escape probability formalism, and recent Hubbard and Puetter models.
TL;DR: In this article, the photoelectron emission from atomic xenon has been simultaneously resolved with respect to photon energy, photon (circular) polarization, electron emission angle, electron kinetic energy, and spin-polarization components by use of synchrotron radiation of wavelengths between 48 and 90 nm from the new dedicated electron storage ring BESSY.
Abstract: The photoelectron emission from atomic xenon has been simultaneously resolved with respect to photon energy, photon (circular) polarization, photoelectron emission angle, electron kinetic energy, and spin-polarization components by use of synchrotron radiation of wavelengths between 48 and 90 nm from the new dedicated electron storage ring BESSY. The angular dependence of the spin polarization and the energy dependence of the dynamical spin parameters experimentally obtained show good agreement with theoretical predictions.
TL;DR: In this paper, an irradiation system of monochromatic uv radiation down to the wavelength of 140 nm was constructed for biological irradiation experiments in the vacuum-uv range using synchrotron radiation (SR) from the electron storage ring.
Abstract: An irradiation system of monochromatic uv radiation down to the wavelength of 140 nm was constructed for biological irradiation experiments in the vacuum-uv range using synchrotron radiation (SR) from the electron storage ring. The system consists of premirror chamber, vacuum-uv monochromator, irradiation chamber, and vacuum systems. Along with the detailed description of all components of the system, the installation at the storage ring and the performance characteristics are presented.
TL;DR: In this paper, the dispersion of the valence bands in a long-chain alkane n -C 36 H 74 was determined by angle-resolved photoemission from an oriented polycrystalline sample using synchrotron radiation.
TL;DR: The real-time method couples the power of x-ray diffraction as a structural probe with the ability to follow kinetics of structural changes with the additional advantage over its static measurement counterpart in that it is more likely to detect transiently stable intermediates if present.
TL;DR: In this paper, the authors proposed two constant deviation and energy-tunable fluorescent microprobe optical designs, which efficiently use X-rays available from bending magnets and insertion devices of synchrotron radiation sources.
TL;DR: The results of the radiation measurements of the laser-produced tungsten plasma let us expect that this source type has the potential to serve as a radiometric transfer standard in the VUV and soft x-ray range below 100 nm.
Abstract: A method is described for measuring the spectral radiant power of VUV and soft x-ray sources using the electron storage ring BESSY as a radiometric standard source of calculable spectral radiant power and degree of polarization. An ellipsoidal grazing incidence mirror stigmatically images the stored electrons or the source under investigation in equal optical conditions into a toroidal grating monochromator. The monochromator can be rotated around its optical axis in UHV conditions to account for different degrees of polarization of the two sources. The accuracy presently available with this method is demonstrated by a measurement of the spectral concentration of radiant intensity of a laser-produced tungsten plasma in the wavelength range between 7 and 100 nm with an overall uncertainty of 10%. A detailed analysis of the contributions to this uncertainty shows that the major part of it is caused by the presently uncertain knowledge of the polarizing properties of the radiometric instrumentation and by the uncertainty of the correction procedure which accounts for the influence of higher diffraction orders of the monochromator grating. The results of the radiation measurements of the laser-produced tungsten plasma let us expect that this source type has the potential to serve as a radiometric transfer standard in the VUV and soft x-ray range below 100 nm.
TL;DR: In this paper, the damage of hydrated lecithin membranes brought about by exposure to wiggler-derived synchrotron radiation at 8.3 keV (1.5 A) was reported.
IBM1
TL;DR: In this article, the authors studied the oxidation of ultra high-vacuum-cleaved GaAs(110) surfaces with high-resolution, core-level photoemission excited with synchrotron radiation, and showed that both subsurface oxidation and multibonding geometries occur already at submonolayer coverages.
Abstract: The oxidation of ultra high-vacuum-cleaved GaAs(110) surfaces has been studied with high-resolution, core-level photoemission excited with synchrotron radiation. The oxidation is spatially and chemically inhomogeneous, and both subsurface oxidation and multibonding geometries occur already at submonolayer coverages.