Showing papers on "Synchrotron radiation published in 1987"

Three-Dimensional X-ray Microtomography

Abstract: The new technique of x-ray microtomography nondestructively generates three-dimensional maps of the x-ray attenuation coefficient inside small samples with approximately 1 percent accuracy and with resolution approaching 1 micrometer. Spatially resolved elemental maps can be produced with synchrotron x-ray sources by scanning samples at energies just above and below characteristic atomic absorption edges. The system consists of a high-resolution imaging x-ray detector and high-speed algorithms for tomographic image reconstruction. The design and operation of the microtomography device are described, and tomographic images that illustrate its performance with both synchrotron and laboratory x-ray sources are presented.

Synchrotron Emission from Shock Waves in Active Galactic Nuclei

Abstract: The origin of the sharp near infrared cutoff in the continuous energy distribution of many compact non-thermal sources (BL Lacs, OVVs, red quasars and certain jets) is considered under the assumption that particle acceleration takes place in shocks. This model predicts a highest frequency v* of electron synchrotron emission which depends principally on the shock velocity and the ratio a of photon to magnetic energy density in the acceleration region. For near relativistic flows and reasonable values of a a spectral cutoff is predicted in the range 3 1014 < v < 2 1015 Hz. The model thus leads to 1) near relativistic flows, 2) a gradual steepening of optical continuum spectra as one follows a jet outwards, 3) a correlation between spectral hardening and luminosity, 4) a correlation between optical spectrum and X-ray emission, 5) a possible synchrotron contribution to the X-ray emission in Quasars from secondary particles, and 6) the production of very high energy particles such as observed in cosmic rays, of up to ~1012 GeV.

X-ray diffraction studies of organic monolayers on the surface of water.

Abstract: We have used synchrotron radiation to study organic monolayers on water (''Langmuir films''). At high monolayer pressures, lead stearate (Pb(C/sub 17/H/sub 35/COO)/sub 2/) shows a powder peak at 1.60 A/sup -1/, implying an area per unit cell of 17.8 A/sup 2/ if the lattice is triangular. The correlation length is about 250 A. Lignoceric acid (C/sub 23/H/sub 47/COOH) shows a similar peak even though no heavy ions are attached. When the pressure is reduced, the peak in lead stearate does not observably move or broaden; below the ''knee'' in the isotherm, however, the peak height decreases slowly with increasing area, implying a first-order melting transition.

Grazing incidence synchrotron x-ray diffraction method for analyzing thin films

Abstract: A method using synchrotron radiation parallel beam x-ray optics with a small incidence angle α on the specimen and 2Θ-detector scanning is described for depth profiling analysis of thin films. The instrumentation is the same as used for Θ:2Θ synchrotron parallel beam powder diffractometry, except that the specimen is uncoupled from the detector. There is no profile distortion. Below the critical angle for total reflection αc, the top tens of Angstroms are sampled. Depth profiling is controlled to a few Angstroms using a small α and 0.005° steps. The penetration depth increases to several hundred Angstroms as α approaches αc. Above αc there is a rapid increase in penetration depth to a thousand Angstroms or more and the profiling cannot be sensitively controlled. At grazing incidence the peaks are shifted several tenths of a degree by the x-ray refraction and an experimental procedure for calculating the shifts is described. The method is illustrated with an analysis of iron oxide films.

Synchrotron radiation-excited chemical-vapor deposition and etching

Abstract: Photoexcited chemical‐vapor deposition (CVD) and etching using synchrotron radiation as an exciting light source were experimentally demonstrated. CVD of silicon nitride film and etching of Si and SiO2 by SF6+O2 gases are described in detail. In several reaction systems, it was found that the surface photoexcitation was an important mechanism. Reaction models for gas‐phase excitation and surface excitation were proposed.

Synchrotron radiation‐excited chemical‐vapor deposition and etching

Abstract: Photoexcited chemical‐vapor deposition (CVD) and etching using synchrotron radiation as an exciting light source were experimentally demonstrated. CVD of silicon nitride film and etching of Si and SiO2 by SF6+O2 gases are described in detail. In several reaction systems, it was found that the surface photoexcitation was an important mechanism. Reaction models for gas‐phase excitation and surface excitation were proposed.

Fluorescence tomography using synchrotron radiation at the NSLS

Abstract: Fluorescence tomography utilizing focussed, tunable, monoenergetic X-rays from synchrotron light sources hold the promise of a non-invasive analytic tool for studying trace elements in specimens, particularly biological, at spatial resolutions of the order of micrometers. This note reports an early test at the National Synchrotron Light Source at Brookhaven National Laboratories in which fluorescence tomographic scans were successfully made of trace elements of iron and titanium in NBS standard glass and in a bee.

New approach to the study of nuclear Bragg scattering of synchrotron radiation.

Abstract: Nuclear Bragg scattering of synchrotron radiation from isotopically enriched /sup 57/Fe/sub 2/O/sub 3/ has been observed at a signal-to-noise ratio of 100:1 without delayed-coincidence techniques. The use of a high-resolution premonochromator providing a 5-meV energy spread and 0.4'' collimation allows for high-resolution studies of dynamical diffraction effects. In particular, the observed intensity of the pure nuclear (7,7,7) reflection implies a dramatic decrease of the effective lifetime due to coherent scattering.

Computerized microtomography using synchrotron radiation from the NSLS

Abstract: Results of microtomography experiments that employ filtered radiation from the National Synchrotron Light Source X-26 Microprobe beam line are presented. These experiments have yielded images of a freeze-dried caterpillar with a spatial resolution of the order of 30 μm and show that the limit on the spatial resolution with the present apparatus will be 1 to 10 μm. Directions for improvement in synchrotron microtomography techniques and some possible applications are discussed.

Special multipole wiggler design producing circularly polarized synchrotron radiation

Abstract: A planar multipole wiggler device which can produce both linearly and circularly polarized synchrotron radiation is proposed Standard wiggler designs have a quasi sinusoidal magnetic field distribution resulting in a - more or less - perfect cancellation of right/left handed circularly polarized photons emitted from successive poles We show here that one can easily generate a periodic but asymmetric magnetic field distribution having a field integral still equal to zero in order to maintain a straight overall direction of the particle trajectory Due to the asymmetry of the field distribution in our device, the synchrotron radiation along the wiggler axis can keep a high degree of circular polarization above or below the particle trajectory plane As compared to standard bending magnets, the proposed device can afford a significant increase of the available flux of circularly polarized light which is typically proportional to the number of magnetic periods As compared now to the two crossed field undulator system, our wiggler device definitively offers a much broader spectral range of emission and far more flexibility regarding energy scanned experiments which might prove to be very difficult with a two crossed field undulator device The wiggler described here should also accomodate any future or already existing machine with common lattices while a two crossed field undulator system is only to work on very low emittance storage rings

Spin-aligned momentum distributions of transition-metal ferromagnets studied with circularly polarized synchrotron radiation.

Abstract: The momentum distributions of the unpaired spin electrons in Fe, Co, and Ni have been measured using circularly polarized x rays produced from an x-ray phase plate developed at the Cornell High Energy Synchrotron Source Estimates of the negative polarization of the $s\ensuremath{-}p$ components of the conduction electrons have been made The spin-dependent transition-metal momentum profiles are compared to theoretical calculations Preliminary results from gadolinium are also presented

A role of cosmic rays in generation of radio and optical radiation by plasma mechanisms

Abstract: The radiation of ultrarelativistic particles is examined in a quasi-uniform magnetic field superimposed by a wide spectrum of magnetic, electric, and electron density inhomogeneities created in a turbulent plasma. The radiation spectrum from a particle of a given energy is shown to acquire a high-frequency power-law tail with the same spectral index as the index ν of small-scale turbulence. For a power-law spectrum of ultrarelativistic electrons, dN(ℰ)/dℰ ~ ℰ−ξ, with a cut-off at some energy ℰmax, the radiation spectrum consists of a few power-law ranges; the radiation intensity may suffer jumps at frequencies which separate these ranges. In the high-frequency range the spectral index ν is determined by small-scale magnetic and electric fields. At intermediate frequencies the main contribution comes from the synchrotron radiation in a large-scale field; the radiation spectrum has an index α=(ζ−1)/2. The same index may be produced by large-scale Langmuir waves. At lower frequencies the radiation spectrum increases owing to the transition radiation caused by electron density fluctuations; in this case the spectral index is equal to ζ+1−ν. The possibility of diagnostics of high-frequency cosmic plasma turbulence from radiation of high-energy particles is discussed. It is shown that the proposed theory may explain some features in the spectra of several cosmic objects.

Compact superconducting SR ring for X-ray lithography

Abstract: A compact synchrotron radiation ring based on a new injection method has been designed as a light source for X-ray lithography, and is now being constructed. This machine consisting of a superconducting weak-focusing single-body magnet is 3 m in outer diameter and 2.2 m in height. The injection method uses half-integer resonance to inject the high-energy and high-intensity electron beams into this small ring of 1 m orbit diameter. The beam injected at 150 MeV is accelerated up to 650 MeV, while the magnetic field is excited from 1.0 to 4.3 T at a rate of 0.02 T/s. Betatron tunes are changed dynamically during this acceleration period. A small cavity of two λ/4 coaxial resonators supplies the acceleration voltage of 120 kV. A vacuum chamber of a hybrid structure contains a beam duct and cryopanels. The vacuum pressure of the duct is 6 × 10 −10 Torr. The beam intensity is 300 mA and its lifetime is longer than a day.

Refinement of simple crystal structures from synchrotron radiation powder diffraction data

Abstract: X-ray powder diffractometry with storage-ring radiation was used to test various aspects of a method for refining simple crystal structures (Si, CeO2 and Co3O4). Excellent powder patterns were obtained with 0.17° resolution parallel slits and 1 A X-rays. The intensities were determined with a double-Gaussian profile-fitting function and used in the powder least-squares refinement program POWLS. Except for Si, the peaks were broadened because of small particle sizes. The R(Bragg) values were in the range 0.4–1.7%.

Charged beam apparatus

Abstract: A charged beam apparatus comprises vacuum vessels for accommodating superconducting coils in a heat-insulating manner, a charged beam vacuum chamber that provides a passage for a charged beam, and a vacuum chamber for synchrotron radiation that is coupled to the charged beam vacuum chamber and through which is passed the synchrotron radiation that is produced by the charged beam when it is bent by the superconducting coils, the vacuum vessels being detachable from the charged beam vacuum chamber.

Angle-, Energy- and Spin-Resolved Photoelectron Emission Using Circularly Polarized Synchrotron Radiation

Abstract: With the development of BESSY a light source of circularly polarized vuv radiation with sufficiently high intensity has become available to make angle- and energy-resolved photoelectron spin-polarization studies with circularly polarized radiation feasible This paper reviews the recent experimental activities performed with free atoms, physisorbed adsorbates and solid surfaces (metals as well insulator) in the past three years The spin-polarization of photoelectrons measured under certain conditions to be almost complete studies atomic effects as auto-ionization resonances in the gas phase as well as even in the photo-emission of adsorbates The cross comparison of photoemission data from Xe in its different structural phases (free atom, adsorbate in different structures and on different substrates, three dimensional crystal) yields symmetry characterizations of the electronic states (assignment of quantum numbers, determination of dipole matrix elements and phase shifts; spin resolved band mapping) and shows the ability of spin-polarization spectroscopy to build a bridge between atomic and surface physics

Generation of Quasi-Circularly Polarized Undulator Radiation with Higher Harmonics

Abstract: Spectral and polarization characteristics of radiation from a relativistic electron travelling along a deformed helix constrained on a surface of an elliptic cylindroid are theoretically investigated. The present theory shows that the radiation has quasi-circular (elliptical) polarization with higher harmonics. It also gives the general expressions for the radiated electric field which contains both helical and plane undulator radiations as special cases.

Monochromatic X-ray irradiation system (0.08-0.4 nm) for radiation biology studies using synchrotron radiation at the photon factory.

Abstract: A monochromatic X-ray irradiation system in the 0.08-0.4 nm wavelength range is described. This uses for the first time, synchrotron radiation at the Photon Factory as an X-ray source (2.5 GeV electron storage ring). It consists of a beam shutter, a Si crystal monochromator, ionization chambers for monitoring exposures, a sample stage, and a control system. The beam is 2.7 × 30 mm at the sample position with a fairly uniform intensity of several kR/min (one C · kg-1 · min-1). The wavelength is an extremely pure Δλ/λ ?? 10-3. A 35 mm culture dish is moved across the vertical height (2.7 mm) of the X-ray beam using a sample scanning stage. This improves the uniformity of the radiation intensity on the sample. The sample can be irradiated under normal or controlled atmospheric conditions. Since 1984, a variety of biological materials have been irradiated, including cultured mammalian cells. Results of yeast cells are presented to illustrate the performance of this irradiation system.

Quantized synchrotron radiation in strong magnetic fields

Abstract: Spectra from electrons making synchrotron transitions in high magnetic fields are calculated using the exact quantum transition rates for Landau states up to n = 500, and the results are compared with spectra calculated from the classical formula and the asymptotic quantum formula. The behavior of the transition rates are examined at low and high harmonics as a function of the spin state of the electron. The calculations confirm those of Herold, Ruder, and Wunner (1982) for low Landau states, extending them to higher states and individual spin state transitions. The results also confirm the dominance of ground-state transitions at high field strengths noted by White (1976). Single particle emissivities for electrons with both spin-up and spin-down in the initial state are calculated using these transition rates. Spectra for thermal electron distributions at transrelativistic temperatures and for steady state injection of monoenergetic electrons with isotropic pitch angles are also presented.

Observational strategies for three‐dimensional synchrotron microtomography

Abstract: We describe essential features of a data set of projection measurements suitable for tomographic imaging with given accuracy and resolution, and apply the results to analyze the use of synchrotron radiation to perform three‐dimensional microtomography. Previously, Grodzins [Nucl. Instrum. Methods 206, 541 (1983)] showed that the number of photons needed to generate an image could be minimized by adjusting the observational energy such that the target’s optical depth FD=2. We correct and extend his results to consider also the spectral distribution of the source. Observational time is minimized at a (typically) lower observational energy where the source flux is larger, even though FD≥2. The results demonstrate that, in principle, synchrotron sources provide sufficient brightness to image small samples with ≂1‐μm resolution.

Scaling to high average powers of a flash x‐ray source producing nanosecond pulses

Abstract: Described here is the scaling of a repetitively pulsed, flash x‐ray source to yield 140‐mW average power in 15‐ns pulses of radiation near 1 A. Interchangeability of discharge anodes has provided for a significant fraction of the output to be extracted in the K lines of Cu, Mo, Nb, and Ag. In less than 1 min of experimental time, a peak spectral density is radiated that exceeds 1×1018 keV/keV. For some applications this device can offer a tabletop alternative to laser plasma x rays and to synchrotron radiation.

Beamstrahlung from colliding electron-positron beams with negligible disruption

Abstract: We present radiative energy loss formulas for beamstrahlung from colliding electron-positron beams which experience negligible disruption, as determined by numerical simulation. Our computer code uses the correct quantum mechanical photon number spectrum for synchrotron radiation emitted by relativistic electrons to simulate with macroparticles the discrete nature of photon emission. For Gaussian beams with small average electron energy loss, we determine energy loss formulas valid for all radiation regimes from classical to extreme quantum mechanical which depend on only two beam parameters, a quantum radiation parameter ϒ0 and a beam energy per unit length, Γ0.

Synchrotron radiation‐excited chemical vapor deposition of SixNyHz film

Abstract: The photochemical vapor deposition of SixNyHz films (y/x≤11) is demonstrated, using the vacuum UV (VUV) from synchrotron radiation (SR) for the first time In the configuration with the beam axis parallel to the substrate surface, the deposition rate achieved is about 005 nm/min for a 100 mA ring current and a 27/133 Pa SiH4/N2 pressure Values of about nine times larger are obtained in the perpendicular configuration It is shown that decomposition of adsorbed molecules by SR irradiation is the primary process involved in deposition in the perpendicular configuration

Confined thermal multicharged ions produced by synchrotron radiation

Abstract: Synchrotron x rays have been used to produce a confined multicharged ion gas near room temperature. Comparison of charge-state-number observations characteristic of ion formation and of ion storage, together with measurements of Ar-to-Ar/sup q/ electron-transfer rate coefficients, provide information to estimate time constants for relaxation to thermal equilibrium and other stored-ion properties important to further development of the technique.

Synchrotron radiation-induced etching of a carbon film in an oxygen gas

Abstract: It was found that a carbon film in an oxygen gas is etched by irradiation of synchrotron radiation (SR). The etching rate was about 3 nm/min for a 100‐mA ring current in an oxygen pressure of 26.7 Pa, and it increased in proportion to the square root of the oxygen pressure and the incident SR beam power. An analysis of the etched pattern indicates that the surface excitation induced by SR irradiation plays the predominant role in the described etching reaction.