Showing papers on "Synchrotron radiation published in 1976"

Measurement of the X-ray polarization of the Crab Nebula

Abstract: The graphite crystal X-ray polarimeters aboard the OSO-8 satellite were used to observe the Crab Nebula for six days from March 11 through March 17, 1976 (UT). Analysis of 15 orbits of quick-look data shows that the polarization and position angles at 2.6 and 5.2 keV are 15.7%(+ or - 1.5%) at 161.1(+ or - 2.8) deg and 18.3%(+ or - 4.2%) at 155.5(+ or - 6.6) deg, respectively. These results confirm the previous measurement and the hypothesis of synchrotron X-ray emission.

X-ray microscopy with synchrotron radiation

Abstract: We have built a microscope for soft χ radiation using zone plates as imaging optical elements. The experiments were done at the Deutsches Elektronen-Synchrotron (DESY), Hamburg, using holographic zone plates and gratings made at the Optical Laboratory of Gottingen Observatory.\" The wavelength region between 1-10 nm is suitable for x-ray microscopy. In this region the image formation is dominated by photoelectric absorption, which depends crit­ ically on the wavelength used and the density and chemical composition of the microscopic object. A great advantage of x-ray microscopy is that biological objects can be examined directly in a living state without severe radiation damage. We used the synchrotron radiation at DESY because of its high intensity and because we could select the wavelength. Figure 1 shows the experimental arrangement. The poly­ chromatic, slightly divergent radiation is dispersed by a 100-mm holographic laminar grating with 600 lines per mil­ limeter used in grazing incidence. A holographically made zone plate with a diameter D = 5 mm, 2600 zones, and a focal length of f = 522 nm for 4.6-nm radiation generates a reduced monochromatic image of the synchrotron source in the object plane. A magnified image of the object is generated by a microzone plate in the image plane. Up to now we used a holographically made microzone plate with a diameter of 1 mm, 850 zones, and a resulting focal length of f = 64.5 mm for Fig. 1. The experimental arrangement.

X-Ray Resonant Raman Scattering: Observation of Characteristic Radiation Narrower than the Lifetime Width

Abstract: Intense tuneable synchrotron radiation was used to perform a high-resolution study of the resonant scattering response of Cu metal in the x-ray regime. One finds in the transition regime from fluorescence to resonant scattering that the linewidth of the emitted radiation becomes narrower than the lifetime-limited width of the fluorescent radiation.

On Understanding Spin-Flip Synchrotron Radiation and the Transverse Polarization of Electrons in Storage Rings

Abstract: A mainly didactic discussion is given of the mechanism for the gradual build up of transverse polarization of electrons and positrons in storage rings. The history and basic results are reviewed briefly. Then an intuitive explanation of the polarization in terms of spontaneous emission via a nonrelativistic magnetic dipole transition in a moving inertial frame is presented and criticized. This simple treatment contains a large part of the essential physics, but not all. It is surprisingly successful for electrons and positrons ($g=2$), becomes exact for large $g$ factors of either sign, but fails badly for particles with $g$ factors of the range $0\ensuremath{\lesssim}g\ensuremath{\lesssim}1.5$. The failure occurs because here the spin-magnetic-moment system cannot be treated even approximately in isolation from the orbital motion. A correct semiclassical description of radiation by a spin system is then given, in direct analogy with semiclassical radiation theory for charged particles ignoring spin. The classical equation of motion for a spin in relativistic motion, derived originally by Thomas, is used to obtain an effective Hamiltonian of interaction of a spin with electromagnetic fields. Emission and absorption of radiation is then described by replacing the classical electromagnetic fields with the appropriately normalized photon fields. The resulting formulas are applicable to charged particles of arbitrary $g$ factor. Expressions are given for the differential spectra in angle and in frequency for numbers of photons and for radiated power, as well as the previously known results for the total transition rates. These results seem of physical interest only for $g=2$ but serve useful pedagogic purposes, refuting some of the expectations of the naive explanation. The various differential spectra are treated in detail for $g=2$ and compared with the corresponding spectra for ordinary synchrotron radiation.

Spectra and optics of synchrotron radiation

Abstract: The spectra, angular distribution, and polarization functions of synchrotron radiation are tabulated in parametric form Numerous graphs of the functions are included, and these can be used for rapid estimation of photon flux as a function of the various parameters The extended synchrotron radiation source is described, and the exact, but unintegrable, equations are derived Properties of this source depend upon at least nine parameters An approximation of the source accurate enough for estimating flux in optical instruments is developed Power and power density in the radiation beam are described and convenient approximations are developed Simple optical transformations are used to illustrate some of the important properties of the extended source

Applications of synchrotron radiation to protein crystallography: preliminary results

Abstract: X-ray diffraction photographs of protein single crystals have been obtained using synchrotron radiation produced by an electron-positron storage ring. The diffracted intensities observed with this unconventional source are a factor of at least 60 greater than those obtained with a sealed x-ray tube using the same crystal and instrumental parameters. Diffraction data have been collected by the precession method to higher resolution and using smaller protein crystals than would have been possible with a conventional source. The crystal decay rate in the synchrotron beam for several proteins appears to be substantially less than that observed with Ni-filtered Cu radiation. The tunable nature of the source (which allows selective optimization of anomalous contributions to the scattering factors) and the low angular divergence of the beam make the source very useful for single crystal protein diffraction studies.

Chemisorption-induced surface umklapp processes in angle-resolved synchrotron photoemission from W(001)

Abstract: Angle-resolved photoemission, using synchrotron radiation, from the chemisorption system W(001)+H shows a very large doublet of peaks at initial energies -1.3 and -0.6 eV for quarter-monolayer coverage which disappear at higher coverage. The emission lobes are strongly peaked in the azimuths and are attributed to essentially pure bulk W transitions. The electrons are emitted in the new directions through the influence of ''extra'' surface reciprocal lattice vectors associated with the hydrogen C (2x2) superstructure. (AIP)

Photoemission of gold in the energy range 30-300 eV using synchrotron radiation

Abstract: Photoemission measurements have, for the first time, been extended to photon energies between 100 and 300 eV Results from polycrystalline gold show amplitude modulation of the $5d$ peaks in the valence band for $100lh\ensuremath{ u}l200$ eV The photoionization cross section of the $4f$ electrons is mapped out in detail from threshold to 280 eV and a narrow full width at half-maximum of 01-02 eV is found Final-state effects are found to be important for the $5p$ excitation

X-ray microscopy of biological objects with carbon kappa and with synchrotron radiation

Abstract: X-ray micrographs of biological objects have been obtained with a resolution better than 1000 angstroms by using poly(methyl methacrylate) x-ray resist and carbon Kalpha or synchrotron radiation. Synchrotron radiation allows short exposure times; storage rings especially designed as radiation sources and improved x-ray resists would make exposure times under 1 second possible.

Application of synchrotron radiation to x‐ray lithography

Abstract: Synchrotron radiation from the German electron synchrotron DESY in Hamburg has been used for x‐ray lithography. Replications of different master patterns (for magnetic bubble devices, Fresnel zone plates, etc.) were made using various wavelengths and exposures. High‐quality lines down to 500 A wide have been reproduced using very soft x rays. The sensitivities of x‐ray resists have been evaluated over a wide range of exposures. Various critical factors (heating, radiation damage, etc.) involved with x‐ray lithography using synchrotron radiation have been studied. General considerations of storage ring sources designed as radiation sources for x‐ray lithography are discussed, together with a comparison with x‐ray tube sources. The general conclusion is that x‐ray lithography using synchrotron radiation offers considerable promise as a process for forming high‐quality‐submicron images with exposure times as short as a few seconds.

High resolution monochromator for the VUV radiation from the DORIS storage ring.

Abstract: The unique properties of the DORIS storage ring at DESY as a synchrotron radiation source are exploited for high resolution spectroscopy in the vacuum ultraviolet. We describe a new experimental set up with a 3-m normal incidence monochromator for wavelengths between 3000 A and 300 A (4 ≤ ħω ≤ 40 eV) using a vertical dispersion plane. The storage ring provides a light flux intense and stable enough for rapid photoelectrical scanning of the spectra with a resolution of 0.03 A in first order.

The angular distribution of photoelectrons from xenon

Abstract: Measurements on the angular distributions of the 4d, 5s and 5p photoelectrons from xenon have been made using synchrotron radiation from a 5 GeV electron synchrotron. The importance of including intershell correlation effects is demonstrated by the results on the 5p electrons. The data indicate not only the limitations of the single-particle theories, but also, in the case of the 5p electrons beyond the 4d ionization threshold, the inadequacies of the present RPAE theory.

Small-angle scattering experiments on biological materials using synchrotron radiation.

Abstract: This article describes an alternative approach to small-angle scattering experiments on biological specimens. The method makes use of the unique properties of synchrotron radiation and provides very fast data acquisition with good resolution. Preliminary experiments on rat-tail tendon are described.

Synchrotron or plasma process emission in narrow-band decimetric type IV bursts

Abstract: Extremely narrow-banded type IV/subd//subm/ events have been selected to test the various proposed emission mechanisms. Emphasis is put on the observed spectral shape and rapid variations in intensity, and plasma-physical stability of the source model. Synchrotron emission in quasi-vacuum is excluded by the observed steep low-frequency spectral slope. Free-free absorption of incoherent synchrotron emission is negligible compared with the Razin effect suppression. However, Razin-suppressed synchrotron emission would lead to unstably high concentrations of energetic electrons. A low-frequency cutoff due to cyclotron-resonance absorption is unlikely. The coherent synchrotron processes are shown to require either an excessively large number of relativistic electrons or an unstable pitch angle anisotropy. Plasma processes seem to be the necessary explanation for the bursts under consideration. (AIP)

Synchrotron x-ray sources: a new tool in biological structural and kinetic analysis.

Abstract: Electron synchrotrons and storage rings are large circular accelerators originally developed for high-energy particle physics. Classical electrodynamics predicts that intense radiation will result from the circular acceleration of the charged particles in the rings. In the last few years it has been demonstrated that this synchrotron radiation as applied to X-ray analysis of biological specimens provides a new tool with which to explore hitherto inaccessible spatial and temporal domains of intact functioning structures. The radiation has a similar origin to that of the continuous spectrum from conventional X-ray tubes, but the X-ray intensities obtainable from the circular accelerators can be a thousand times greater than those of laboratory line sources. Although Cauchois et al (1) in 1963 had already pointed out the relevance of synchrotron radiation to biological diffraction, only in the last few years have molecular biologists both felt it necessary and been given an opportunity to work with these large and costly machines (2). In this review we discuss the following aspects of the use of synchrotron radiation in studying biological structures: first, the types of research problems for which the conventional application of X-ray analysis is near its technical or theoretical limits, and for which synchrotron radiation opens up new prospects; second, X-ray sources from a comparative point of view, showing the superiority of synchrotron sources for several applications; third, the essential technical details of the optical apparatus and ancillary equipment needed for effective use of a synchrotron light beam in both static and kinetic diffraction experiments; and finally, mention is made of some other applications of synchrotron radiation.

Photoemission from Cu valence bands using 50--175-eV synchrotron radiation

Abstract: Photoemission spectra of the 3d valence band of polycrystalline Cu were studied using synchrotron radiation of energy 50 120 eV but failed in the region h..nu.. approx. = 90 eV. Fair agreement between experiment and theory was obtained when momentum broadening in the final state was included. The largest broadening was required around h..nu.. = 90 eV. A minimum in the photoelectron mean free path at this energy is discussed as a possible source of broadening. The observed changes in spectral shape for 50 < or = h..nu.. < or = 70 eV are attributed to direct transitions; the changes are found to arise mainly from the angular part of the transition matrix element. (AIP)

Double ionisation of noble gases.II Formation by photon impact.

Abstract: Using synchrotron radiation and a new two-grating monochromator to remove higher-order components, the relative intensities of double-photoionization transitions have been measured in helium, neon, ...

Lossy radial diffusion of relativistic Jovian electrons

Abstract: The radial diffusion equation with synchrotron losses is solved by the Laplace-transform method for near equatorially mirroring relativistic electrons. The evolution of a power-law distribution function is found, and the characteristics of synchrotron burnoff are stated in terms of explicit parameters for an arbitrary diffusion coefficient of a specific form. The peaking of the 10.4-cm volume emissivity from Jupiter at an L shell of about 1.8 provides an estimate of the diffusion coefficient in the radiation belts; one value is suggested as the appropriate modification, for an equatorial field strength of 4.2 G, of the Birmingham et al. (1974) result. Nonsynchrotron losses are included phenomenologically; from the phase-space densities reported by McIlwain and Fillius (1975), the particle lifetime is estimated. Asymptotic forms for the distribution in the strong synchrotron loss regime are provided.

Atomic cross-section effects in soft-x-ray photoemission from Ag valence bands

Abstract: The relative photoemission intensity from the Ag 4d valence band (VB) was studied as a function of photon energy using 32--250 eV synchrotron radiation. A sharp decrease in intensity of more than an order of magnitude was observed in the range 100 or = 150 eV range in order to bridge the ultraviolet-photomission to x-ray-photoemission gap. (AIP)