Showing papers on "Synchrotron radiation published in 1993"

CLULU: An experimental setup for luminescence measurements on van der Waals clusters with synchrotron radiation

Abstract: We describe a new experimental setup for photoluminescence spectroscopy on van der Waals clusters. It consists of a molecular beam apparatus with a cluster beam installed behind a high intensity vacuum ultraviolet synchrotron radiation beamline. Special emphasis was given to the design of a very intense cluster source which can also be used for the preparation of quantum clusters (He,H2). For the determination of the cluster size a time‐of‐flight mass spectrometer can be attached to the setup. In addition, an atomic cross jet is installed in the experimental chamber which can be used for mass separation or for doping of the clusters. The luminescence light can be recorded with several different detectors or spectrally analyzed with a secondary monochromator which is equipped with a position sensitive detector. The pulsed nature of synchrotron radiation provides the basis for time‐resolved measurements in the regime 100 ps–3 μs.

Synchrotron x-ray microprobe determination of chromate content using x-ray absorption near-edge structure

Abstract: X-ray absorption near-edge structure (XANES) has been applied to the quantitative analysis of chromate (CrO[sub 4][sup 2[minus]]) content in oxides, silicate glasses, and simulated cementitous waste forms. The method uses the normalized area of a pre-edge peak (bound-state transition) in XANES spectra acquired with the synchrotron X-ray microprobe on beam line X26A at the National Synchrotron Light Source. The estimated accuracy of the technique is [+-] 5% in terms of Cr[sup 6+]/total Cr. The minimum detection limit approaches 10 ppm Cr[sup 6+] using a 150-[mu]m synchrotron X-ray beam. These results demonstrate the value of synchrotron-based microXANES for the nondestructive quantification of the first-row transition metal species present as tetrahedral oxyanions. 12 refs., 3 figs., 3 tabs.

SiO2/Si(100) interface studied by Al Kα x‐ray and synchrotron radiation photoelectron spectroscopy

Abstract: Both synchrotron radiation photoemission spectroscopy (PES) and Al Kα photoelectron spectroscopy (XPS) are used to determine the suboxide distribution at SiO2/Si (100) interfaces. High resolution PES measurements clearly resolved various suboxides with chemical shifts of 0.97, 1.80, and 2.60 eV for Si+1, Si+2, and Si+3, respectively. A total of 9.3×1014 atoms cm−2 of suboxide is found by PES measurements while only 4.2×1014 atoms cm−2 is measured by XPS on the same sample. This discrepancy is neither caused, as previously believed, by a difference in SiO2/Si (100) quality nor by a difference in methodology in data analysis. The possible factors, e.g., electron mean‐free path and photoionization cross section, which contribute to the difference between PES and XPS data, are considered.

Particle accelerator physics : basic principles and linear beam dynamics

Abstract: This text serves as an introduction to the field of high-energy particle accelerator physics and particle-beam dynamics. It covers the dynamics of relativistic particle beams, the basics of particle guidance and focusing, lattice design, the characteristics of beam transport systems and circular accelerators. Particle-beam optics is treated in the linear approximation, using sextupoles to correct for chromatic aberrations. Perturbations to linear beam dynamics are analyzed in detail and correction measures are discussed. Basic lattice design features and building blocks leading to the design of more complicated beam transport systems and circular accelerators are studied. Characteristics of synchrotron radiation and quantum effects due to the statistical emission of photons on particle trajectories are derived and applied to determine particle-beam parameters. The discussions specifically concentrate on relativistic particle beams and the physics of beam optics in beam transport systems and circular accelerators such as synchrotrons and storage rings.

Lectures on the Free Electron Laser Theory and Related Topics

Abstract: Theory of charged beam transport systems and of synchrotron radiation single mode low gain FEL theory single mode high gain FEL theory the low gain pulse propagation problem the high gain pulse propagation problem three-dimensional effects in FEL operating configurations quantum theory of FEL.

Simultaneous time resolved SAXS and WAXS experiments using synchrotron radiation

Abstract: Instrumentation has been developed which offers the possibility of performing simultaneous time resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) experiments in the range from approximately 0.007–0.21 A −1 and 0.31–4.2 A −1 . A synchrotron SAXS beamline is therefore equipped with two gas filled proportional detectors. The ultimate system time resolution will be of the order of 1 μs. Successful test experiments have been performed on block copolymer samples and polyethylene.

Determination of crystal structures from limited powder data sets: crystal structure of zirconium phenylphosphonate

Abstract: The structure of zirconium phenylphosphonate, Zr(O 3 PC 6 H 5 ) 2 , was solved based on a combination of modeling techniques and Patterson methods and refined by Rietveld methods. Powder diffraction data were collected using synchrotron radiation (λ= 1.3087 A). The crystals belong to the space group C2/c with a=9.0985 (5), b=5.4154 (3), c= 30.235 (2) A and β=101.333 (5) o . The reliability factors are R wp =0.129, R p =0.095, R F =0.023 and the statistically expected R wp =0.02. In the c-axis projection the structure resembles very closely that of α-zirconium phosphate. The phenyl groups are inclined by about 30 o to the c axis and also tilted from the ab plane

Synchrotron X-ray study of the electron density in α-Al2O3

Abstract: Structure factors for synthetic haematite, α-Fe 2 O 3 , have been measured for two small crystals using focused λ=0.7 A synchrotron radiation. The structure factors from the two data sets are consistent. Approximate symmetry in the concordant densities, related more closely to the Fe-Fe geometry than to the nearest-neighbour Fe-O interactions, is similar to that in the corundum α-Al 2 O 3 structure. Deformation density maxima are located at the midpoint of the Fe-Fe vector along the c axis, on a common face for O-octahedra, perpendicular to c. Maxima also occur at the midpoint of the Fe-Fe vector bisecting the edges of the O-octahedra. These results are in accordance with theoretical predictions for metal-metal bonding

The Taffy' galaxies UGC 12914/5

Abstract: The interacting spiral galaxy pair UGC 12914/5 was mapped with the 'VLA' for a 1.49 GHz atlas of the IRAS Bright Galaxy Sample. Half of the flux from UGC 12914/5 arises from the gap between UGC 12914 and UGC 12915, across which the radio contours are drawn like filaments of taffy. The bright radio continuum connecting UGC 12914 with UGC 12915 is a synchrotron source which therefore probably contains both cosmic rays and magnetic fields. It is suggested that the filaments were stripped from UGC 12914 and UGC 12915 as their stellar disks interpenetrated during a recent encounter; this implies that the radio bridge is a relic whose properties contain information about direct collisions of galaxies with gaseous disks. New maps have been made of the radio continuum and H I line emission from UGC 12914/5 in order to verify the stripping hypothesis.

Radiation from magnetized accretion disks in active galactic nuclei

Abstract: We present a model of AGN based on accretion disks around 10 exp 8 solar mass black holes, which incorporates a strong magnetic field in the disk, with loops above the disk in which B is about 100 G. The magnetic energy in the loops dissipates, accelerating electrons to relativistic energies. The electrons emit synchrotron and inverse-Compton radiation, much of which is reflected or scattered by gas in the disk. We calculate the emitted spectrum from infrared to gamma rays. Of the total emission, 23 percent goes into a nu exp -1 power law and 77 percent into thermal radiation at 24,000 K (due to the disk, which is heated by nonthermal radiation and energetic ions). The model accounts quantitatively for the X-ray and gamma-ray backgrounds, and it accounts qualitatively for certain features observed in individual AGNs: a far-infrared cutoff, a minimum at a few microns, the ultraviolet bump, the Compton reflection bump at about 30 keV, and a gamma-ray tail.

Synchrotron radiation light-source apparatus and method of manufacturing same

Abstract: A synchrotron radiation light-source apparatus is provided in which the characteristics of synchrotron radiation generated by bending electromagnets can be made uniform, and emittance can be made smaller to increase brightness. The synchrotron radiation light-source apparatus for bending the traveling direction of an electron beam with bending electromagnets and for emitting synchrotron radiation includes deflecting electromagnets which cause a negative value (-dBy/dx) of a magnetic-field gradient gradually to increase after gradually decreasing in the traveling direction of the electron beam, that is, along the length of the bending electromagnets, so as to form a smooth recessing distribution, or to increase in a step-like manner after decreasing in a step-like manner.

X-ray science and technology

Abstract: X-rays and their properties: Discovery of x-rays X-ray definitions The early days of x-ray science X-ray interactions X-ray emission processes X-ray optics Applications and uses of x-rays. Electron-impact x-ray sources: X-ray generation processes Uses of electron-impact x-ray sources comparison with other x-ray sources. Synchrotron radiation sources: Particle accelerators Synchrotron radiation Electron storage rings as radiation sources Insertion devices the SRS at Daresbury Design of a minimum-emittance lattice. Plasma x-ray sources: Plasma parameters Emission processes in plasmas Line emission from plasmas Continuum emission from plasmas Plasma x-ray sources X-ray lasers. The interactions of x-rays: Coherent x-ray scattering and diffraction Diffraction by crystals Crystal structure determination Anomalous dispersion Methods of solving the phase problem X-ray optical properties Kramers-Kronig analysis for the optical constants Contributions to atomic scattering cross sections EXAFS. X-ray detectors: X-ray film Resists Channel electron multipliers Microchannel plates Gas detectors Scintillation detectors Phospors Silicon detectors. Reflective optics for x-rays: The Fresnel equations Grazing incidence mirrors Compound systems Performance of grazing incidence optics Manufacture of grazing incidence optics Applications of grazing incidence mirrors Crystal optics Multilayer mirrors Multilayer mirror systems Manufacture of multilayer mirrors Applications of multilayer mirrors Bragg-Fresnel optics. Diffactive x-ray optics: Plane diffaction gratings X-ray reflection gratings X-ray transmission gratings Manufacture of diffraction gratings Zone plates Curved gratings Future developments.

On‐line small‐angle and wide‐angle x‐ray scattering studies on melt‐spinning poly(vinylidene fluoride) tape using synchrotron radiation

Abstract: On-line small-angle and wide-angle x-ray scattering experiments were performed during the melt spinning of polyvinylidene fluoride using the DESY synchrotron light source. In these studies, the melt-spinning apparatus consisting of a screw extruder, a metering pump, and a take-up motor system were assembled on two separate stepper-motor-driven platforms. To investigate the structure development during crystallization, the tape location at the desired distance from the die could be positioned at the beam level with synchronous vertical movement of extruder and take-up platforms

Radio spectral ageing in a random magnetic field

Abstract: I study the ageing of radio synchrotron emission from relativistic electrons in a random magnetic field. There is a range of break frequencies corresponding to the range in field strength, so that the sharp break in the spectrum given by the Jaffe-Perola model is not always seen, and the spectra can be very similar to that of the Kardashev-Pacholczyk model. This explains the good fit of the Kardashev-Pacholczyk model to observations, even though the Jaffe-Perola model is more physically reasonable. The lack of an exponential break in the spectrum does not mean that pitch angle scattering does not occur. In the presence of inverse Compton losses, the spectral shape is strongly dependent on rms field strength, allowing equipartition estimates to be checked

Optical characterization of porous silicon by synchrotron radiation reflectance spectra analyses

Abstract: The electronic structure of porous Si(PS) has been characterized by optical reflectance spectra analyses. The reflectance spectra of PS were measured in the photon energy range of 2–27 eV using a synchrotron radiation source. The reflectance at the low energy region was calibrated by the corresponding absolute value which was separately determined from spectroscopic ellipsometry. The spectral response of optical constants were calculated by the Kramers–Kronig analysis. Our results indicate that PS retains some of the characteristic optical features of crystalline Si, and that a blue shift in the absorption edge occurs in PS.

Molecular orientation in thin films of bis(1,2,5-thiadiazolo)-p-quinobis(1,3-dithiole) on graphite studied by angle-resolved photoelectron spectroscopy.

Abstract: Angle-resolved ultraviolet photoelectron spectra using synchrotron radiation were measured for oriented thin films of bis(1,2,5-thiadiazolo)-p-quinobis(1,3-dithiole) on a cleaved highly oriented pyrolytic graphite (HOPG) surface. The observed takeoff angle dependence of the photoelectron intensity was analyzed by using the independent-atomic-center approximation and modified neglect of diatomic overlap molecular-orbital calculations. The calculated results agree well with the experimental ones. From the comparison between these results, the molecules in the thin film are estimated to lie flat with the inclination angle β≤10 o to the HOPG surface

The X-ray-emitting trail of the nearby pulsar PSR1929+10

Abstract: The paper reports the detection by the Rosat satellite of a nebula associated with the nearby pulsar PSR1929 + 10, which is of a type different from the pulsar-wind nebulae produced by direct interaction of the relativistic wind from older pulsars with the interstellar medium (ISM) (Blandorf et al., 1973). The PSR1929 + 10 nebula appears as a linear diffuse X-ray feature in the direction opposite to the pulsar's proper motion, with the pulsar wind confined by the ram-pressure arising from the high velocity of the pulsar through the ISM. This results in a trail of relativistic electrons with enhanced emissions of synchrotron radiation.

Resonant diffraction of synchrotron radiation by a nuclear multilayer.

Abstract: We report the observation of nuclear resonant diffraction of synchrotron radiation by a synthetic multilayer. The nuclear period of the ${[}^{57}$Fe(22 \AA{})/Sc(11 \AA{})/Fe(22 \AA{})/Sc(11 \AA{})\ifmmode\times\else\texttimes\fi{}25 multilayer was chosen to be twice the electronic period to obtain a pure nuclear Bragg reflection. Strong enhancement of the radiative scattering channel provided a fast time response for the $^{57}\mathrm{Fe}$ resonant scattering at the Bragg peak, with a decay time of 4 ns. The nuclear multilayer will be useful as a narrow bandpass monochromator for synchrotron radiation.

GISAXS : glancing incidence small angle X-ray scattering

Abstract: In this method, the incident beam is totally externally reflected from a surface or substrate, followed by small-angle scattering of the refracted (evanescent) beam by the surface region. As one example, GISAXS can provide size information on islands associated with film growth. The technique is described, along with examples from studies of Au on glass, and InAs on silicon. In contrast to TEM this technique is nondestructive, can be done in situ, provides excellent sampling, does not necessarily require synchrotron radiation, and is not limited to thin or conducting substrates

Weibel instability in relativistically hot magnetized electron-positron plasmas

Abstract: A linear stability analysis is carried out for the Weibel instability in relativistic magnetized electron–positron‐pair plasmas, with the propagation direction parallel to the background magnetic field. The instability in the ultrarelativistic regime, with the typical Lorentz factor γ much greater than unity, is emphasized for its relevance to astrophysical sources of synchrotron radiation. Detailed stability properties are examined, in the ultrarelativistic regime, for two model distribution functions, the water‐bag distribution function, and a smooth distribution function. The dispersion relations are obtained in closed analytic forms for both distribution functions. The necessary and sufficient conditions for instability are determined when the temperature along the background magnetic field is cold (T∥=0). The dispersion relations are solved numerically with T∥≠0 over a wide range of system parameters to determine the detailed dependence of the instability on the strength of the background magnetic fi...

Soft-x-ray emission insulators: Spectator versus normal emission.

Abstract: We investigate the excitation energy dependence of the boron [ital K] soft-x-ray emission of B[sub 2]O[sub 3] and hexagonal-BN using synchrotron radiation. When exciting into the core exciton state the spectra are shifted to lower energy by 1.5 and 1.8 eV, respectively. This shift is found to be a result of phonon relaxation and differences in initial-and final-state electronic screening.

Magnetic spectromicroscopy from Fe(100)

Abstract: Magnetic domains on an Fe(100) surface have been imaged by means of energy‐resolved photoemission microscopy. We excited the photoelectrons with circularly polarized synchrotron radiation in the soft x‐ray region, and employed the effect of magnetic circular dichroism in the emitted photoelectrons in order to obtain contrast between differently oriented magnetic domains. This new approach offers a surface sensitive way to combine chemical and magnetic information on a microscopic scale.

Time resolved nuclear resonant scattering from 119Sn nuclei using synchrotron radiation.

Abstract: Nuclear resonant scattering of synchrotron radiation from $^{119}\mathrm{Sn}$ nuclei at 23.87 keV has been observed. The combination of a novel nested crystal monochromator and a $^{119}\mathrm{SnO}_{2}$/Pd based grazing incidence antireflection film was used to investigate the M\"ossbauer parameters of a tin containing powder sample in a forward scattering experiment.

Band-structure effects in the excitation-energy dependence of Si L2,3 x-ray-emission spectra.

Abstract: Si L 2.3 x-ray emission stimulated with narrow-band synchrotron radiation has been studied as a function of excitation energy. In strong contrast to crystalline silicon, amorphous silicon yields emission spectra that are independent of the excitation energy, thereby demonstrating that long-range order plays a necessary role in the excitation-energy dependence of the crystalline emission

Diamond crystal X-ray optics for high-power-density synchrotron radiation beams

Abstract: Man-made perfect single crystal isotopically-enriched diamond is demonstrated to be an excellent X-ray monochromator even when subjected to the highest incident power density expected at third-generation synchrotron source undulator beam lines. Double-crystal rocking curve tests of a diamond (400) wafer exposed to an X-ray power density of 207 W/mm2 (75 W total power) revealed just 1 arc sec of induced thermal distortion integrated across the beam footprint.

Intensity Enhancement in Asymmetric Diffraction with Parallel-Beam Synchrotron Radiation

Abstract: An intensity enhancement obtained from asymmetric diffraction with a fixed incident angle α has been studied. Parallel-beam synchrotron radiation with λ = 1.54 A (Stanford Synchrotron Radiation Laboratory) and λ = 1.53 A (Photon Factory) was used to collect powder diffraction patterns of Si, CeO2 (α = 5 and 10°) and monoclinic ZrO2 (α = 10°). The synchrotron-radiation data were analyzed using single-reflection profile fitting and whole-powder-pattern fitting techniques. The integrated intensities in the asymmetric diffraction were compared with those of symmetric diffraction obtained by the conventional θ–2θ scanning technique. An intensity, after correction for a limited height of counter aperture, was enhanced by factors of 1.8 (α = 5°) and 1.7 (α = 10°) at the maximum in asymmetric diffraction and its magnitudes agreed well with those calculated from theory.

Comment on : measurement of the ratio of double-to-single photoionization of helium at 2.8 kev using synchrotron radiation

Abstract: A Comment on the Letter by J. C. Levin [ital et] [ital al]., Phys. Rev. Lett. 66, 968 (1991).

Circularly polarized soft X-rays in the photon energy range 30–2000 eV at the BESSY SX700/3

Abstract: Research using circularly polarized soft X-ray synchrotron radiation has boomed during the last few years. In this paper we want to report on one of the beamlines for the production of such light at BESSY.