Showing papers on "Synchrotron radiation published in 1988"

Introduction to synchrotron radiation

Abstract: Synchrotron radiation - a unique tool for many disciplines Synchrotron radiation sources and instrumentaion Optical spectroscopy and EXAFS Photoemission spectroscopy Elastic X-ray scattering Synchrotron radiation in technology and medicine Desorption, microscopy, fluorescence, and other synchrotron radiation techniques Future research opportunities.

Design and performance of an imaging plate system for X-ray diffraction study

Abstract: A new readout system for a BaFBr: Eu2+ photostimulable phosphor screen (imaging plate) was constructed by modifying a drum scanner, with a design optimized for X-ray diffraction and scattering applications. An effort was made to achieve a high detective quantum efficiency below 20 keV, a small pixel size (25 μm × 25 μm), a low quantization noise (0.22%) using 12-bit A/D converters, and the capability to cover an inherent dynamic range (1:105) of the photostimulated luminescence by using two photomultiplier tubes. This system is being used in several synchrotron radiation experiments: Laue diffraction of protein crystals, small angle diffraction from a single muscle fiber, powder diffraction from crystals in a diamond anvil cell, and time-resolved small-angle X-ray scattering from a synthetic polymer during stretching.

The Synchrotron Boiler

Abstract: The steady energy distribution of particles emitting and absorbing synchrotron radiation in compact sources is discussed, under the assumption of constant injection of energetic particles. It is shown that synchrotron reabsorption is an important source of heating for low-energy electrons. Since they efficiently exchange energy with the self-absorbed radiation field, their steady distribution is quasi-thermal, up to the Lorentz factor gamma(t) related to the synchrotron self-absorption frequency. The usual distribution, found by balancing injection and cooling rates, is appropriate above gamma(t). 11 references.

Apparatus for acceleration and application of negative ions and electrons

Abstract: An apparatus for generating X-rays from electron synchrotron radiation or beams of accelerated ions for ion radiography or ion therapy includes a source of electrons and a source of ions, both of which are connectable to preaccelerators. The preaccelerators supply the appropriate type of charged particle to a synchrotron accelerator which accelerates ions to an energy level that is appropriate for radiography or therapy and which accelerates electrons to a level that generates X-rays by synchrotron radiation in a useful frequency range. The accelerator system also includes a storage ring into which particles are switched and circulated for later use. Electrons are extracted from the synchrotron and injected into the storage ring by fast extraction using a kicker magnet and a septum magnet. They then circulate in the storage ring for periods of hours generating X-rays which may be used for lithography of computer chips with submicron resolution. The energy loss because of this radiation is continuously replaced by a radio-frequency acceleration system. During the period that electrons are circulating in the storage ring, the synchrotron may be utilized to accelerate ions for ion radiography or ion therapy with beam extracted from the synchrotron by stripping extraction through thin foils. Other simultaneous uses for the ions or electrons from the preaccelerator may prove advantageous.

Photoelectron microscopy with synchrotron radiation

Abstract: Real‐time images produced by photoelectrons from metal and semiconductor samples have been generated using synchrotron radiation. A single electrostatic objective lens coupled to a two‐stage image intensifier has been used to evaluate the feasibility of combined imaging and spectroscopy with photoelectrons in the ultraviolet and soft x‐ray regions. Images were generated using photon energies ranging from 9 to 160 eV. The use of monochromatic synchrotron radiation provides a unique capability for generating image contrast by digital subtraction of images formed with photon energies above and below a core‐level binding energy. A simple electron‐optical objective lens produces images with a few microns resolution, and adequate sensitivity to image 45‐eV kinetic energy electrons using bending magnet radiation. Calculations based on these experiments show that comparable resolutions are possible for combined microscopy and spectroscopy with electrons of order 100‐eV kinetic energy using currently available bending magnet synchrotron radiation. Calculations for expected performance from undulator sources are presented.

Synchrotron X-ray Diffraction Measurements of Single-Crystal Hydrogen to 26.5 Gigapascals

Abstract: The crystal structure and equation of state of solid hydrogen have been determined directly to 26.5 gigapascals at room temperature by new synchrotron x-ray diffraction techniques. Solid hydrogen remains in the hexagonal close-packed structure under these pressure-temperature conditions and exhibits increasing structural anisotropy with pressure. The pressure-volume curve determined from the x-ray data represents the most accurate experimental measurement of the equation of state to date in this pressure range. The results remove the discrepancy between earlier indirect determinations and provide a new experimental constraint on the molecular-to-atomic transition predicted at higher pressures.

X-ray microprobe using multilayer mirrors

Abstract: Multilayer reflectors for the X-ray region have now progressed beyond the experimental stage to the point where they can be relied upon as optics for experimental systems, in synchrotron radiation research as well as in other fields. This paper reviews the design considerations for an X-ray microprobe, and summarizes experience with prototypes tested at both SSRL and NSLS. The optical systems described employ multilayer-coated spherical mirrors arranged in the Kirkpatrick-Baez configuration to demagnify the X-ray source by a factor of several hundred. By this means a spot of X-rays less than 10 μm square can be produced. The optical aberrations and other factors that limit the performance are detailed, and possible ways to improve the performance are discussed. In the prototypes the spot is directed on the specimen which is carried on a stage that can be translated horizontally and vertically. The characteristic fluorescent X-rays excited by the focused 10 keV photons are analysed by an energy-dispersive Si(Li) detector, so that by scanning the stage an elemental concentration map of the specimen is built up. In a companion paper [A.C. Thompson, J.H. Underwood, Y. Wu, R.D. Giauque, K.W. Jones and M.L. Rivers, these Proceedings, p. 318] some experimental programs are described, and estimates of the elemental sensitivity are provided.

Synchrotron radiation source having adjustable fixed curved coil windings

Abstract: A synchrotron radiation source contains a particle track with a curved track section. A beam guiding chamber surrounding the particle track has an exit opening for the synchrotron radiation leading in an outward direction. A magnetic device has superconducting coil windings located on both sides of the particle track having a peripheral outer rim. In addition, a device for the mechanical fixation of the superconducting coil windings is provided. The fixation device has at least one support element at the peripheral outer rim of the magnetic device. The support element is located further outward than the exit opening for the synchrotron radiation and acts substantially perpendicular to the direction of the radiation. The support element is covered from the synchrotron radiation by a radiation absorber. The use of a support element provides simple and safe support for the superconducting coil windings in the area of the radiation exit opening.

Simple method for focusing x rays using tapered capillaries.

Abstract: A new method of focusing x rays is described using appropriately tapered capillaries. The x rays are incident on the inner surface of the capillary below the critical glancing angle and reflect due to total external reflection. By appropriately narrowing the capillary, the x rays can thus be focused in a broad band of energies. The theory of the effect and optimum taper is described. A measurement verifying the focusing capability of the method is presented. The method appears practical for focusing bending magnet synchrotron radiation around 8 keV down to a diameter of 10 mum from an initial dimension of 1-mm(2) incident cross section with an attenuation of the total energy of ~2, i.e., an increase in the intensity per unit area of 6.5 x 10(3). Greater focusing is possible with softer x rays and from undulator sources. The wide-ranging applicability of the technique is discussed.

Acquisition of power diffraction data with synchrotron radiation

Abstract: During the past year, a dedicated triple-axis powder diffractometer has been in routine operation at the Brookhaven National Synchrotron Light Source as a user-oriented facility. The diffractometer is designed to allow easy interchange between energy-dispersive and monochromatic beam experiments. In the latter mode of operation, high resolution data have been collected for a variety of samples with the use of the crystal-analyser technique, and in several cases these data sets have been used successfully for structure solution and Rietveld refinement. Several aspects of data acquisition at a synchrotron beam-line are described, and some of the different types of scattering geometry which have been used are discussed. Simple expressions are given for the instrumental resolution function expressed as the angular variation of peak widths for each of these. The peak shapes observed for a reference sample of Si on the present triple-axis instrument are well described by the convolution of Gaussian and Lorentzian functions, and the angular dependence of the Gaussian component is in excellent agreement with the corresponding calculated instrumental function. One of the most important considerations for each type of experiment is the necessary compromise between intensity Ilnd resolution over a wide range of scattering angles, and some of the available options are discussed. In particular, the use of Ge(440) and LiF(400) analyser crystals gives a focussing minimum at relatively high angles (28 ::::: 50· at 1·54 A), a highly desirable feature for Rietveld analysis of complex structures. Absolute intensities from reference samples of Si and Ce02 are calculated for these and several other scattering configurations involving both fiat-plate and capillary geometry to illustrate this compromise.

X-ray Absorption Spectroscopy in the Dispersive Mode with Synchrotron Radiation: Optical Considerations

Abstract: Aspects of the optics of the energy-dispersive scheme for X-ray absorption spectroscopy are discussed. The idea of a set of monochromatic focus points related to a set of local Rowland circles is introduced to account for the source-size effect on the energy resolution. It is shown that there exists an optimized location of the position-sensitive detector where the energy resolution is no longer source-size dependent. In addition, the stability of the dispersive optical system has been estimated and a 10 meV energy-scale reliability is currently achieved.

Piperazine silicate (EU 19): the structure of a very small crystal determined with synchrotron radiation

Abstract: Single-crystal diffraction data have been recorded for a very small crystal of dimensions 8 x 18 × 175 ~rn 3. From these data the structure of piperazine silicate (EU 19) has been determined and refined to R = 0.094 for 490 observed reflections. Data collection for such a crystal has been made practicable by the high intensity of the Daresbury Synchrotron Radiation Source and the Enraf-Nonius FAST area detector diffractometer. The potential of this synchrotron radiation method for other small crystals including proteins is discussed. Crystal data: 2+ • 2

Synchrotron-radiation limit on the focusing of electron beams.

Abstract: It is shown that there is an essential limit on the focusing of electron beams due to synchrotron radiation in the final focusing lens of a linear collider. The minimum possible beam size is determined almost only by an invariant emittance of a beam which is given at the entrance of a linear accelerator.

Undulator generating any kind of elliptically polarized radiation

Abstract: A new type of undulator with crossed and retarded magnetic fields which enables us to obtain any kind of elliptically polarized synchrotron radiation from relativistic electrons was developed. This undulator was installed in a straight section of the electron storage ring, TERAS, and its polarization characteristics were investigated. The experimental results proved that this device can generate linearly or circularly polarized synchrotron radiation which would be very useful in polarization modulation spectroscopy.

Is there any beam yet? Uses of synchrotron radiation in the in situ study of electrochemical interfaces

Abstract: The advantages of employing synchrotron radiation for the in situ study of electrochemical interfaces are discussed with emphasis on the techniques of surface EXAFS (extended X-ray absorption fine structure) and X-ray standing waves. The principles behind the techniques are briefly considered followed by a discussion of recent experimental results. Examples include the study of under potentially deposited metallic monolayers, polymer films on electrodes, and in situ measurement of adsorption isotherms. The authors conclude with an assessment of future directions.

Decay pathways of excited electronic states of Group IV tetrafluoro and tetrachloro molecular ions studied with synchrotron radiation

Abstract: This paper describes experiments to probe the dynamics and decay pathways of the C 2T2 and D 2A1 excited electronic states of Group IV tetrahalide molecular ions MX+4 (M=C, Si, Ge; X=F, Cl) in the gas phase. Tunable vacuum UV radiation from a synchrotron source is used to ionize MX4 into these electronic states of MX+4. Flouorescence from ions initially produced or from fragments is monitored undispersed by a suitable pm tube. When the synchrotron is operated cw, such synchrotron‐induced fluorescence spectra give energy thresholds for fluorescence, and in favorable cases an estimate of the fluorescence quantum yield (of MX+4 C or D) can be made. When the synchrotron is operated pulsed, radiative lifetimes can be measured as a function of excitation energy. The fluorides and chlorides display very different decay properties. The dynamical behavior of these states is rationalized (a) with respect to their spectroscopic properties, and (b) with respect to the dissociation channels energetically ‘‘open’’ ...

Mosaic crystal monochromators for synchrotron radiation instrumentation

Abstract: The diffraction properties of perfect single crystals match the properties of X-ray beams emitted by high energy storage rings in many cases. However, under certain circumstances imperfect crystals are better adapted to the experimental requirements and should therefore be considered as devices for beam definition. In particular progress has recently been made in the development of low mosaic spread beryllium and silicon single crystals. The results of calculations given in the present paper show that up to two orders of magnitude can be gained in flux on the sample when perfect crystals are replaced by mosaic crystals.

X-ray microscopy

Abstract: Developments in microscopy using soft X-rays (energies between about 100 eV and 2 keV) over the last ten years or so are reviewed. The main advances have been in intense sources, principally synchrotron radiation and plasma sources and in X-ray optical components such as grazing incidence reflectors, multilayer mirrors and zone plates. The different types of X-ray microscopy are described and images obtained are compared with those from the much better established techniques of electron and optical microscopy. Finally, prospects for the future are discussed.

Experimental verification of a new spin-polarization effect in photoemission: Polarized photoelectrons from Pt(111) with linearly polarized radiation in normal incidence and normal emission

Abstract: A theoretical prediction of a new spin effect by Tamura, Piepke, and Feder has been experimentally verified: Photoelectrons can be polarized even if the photoemission is performed with linearly polarized radiation and even if it is studied in the highly symmetrical setup of normal incidence and normal emission. Radiation with energies between 21 and 22.4 eV ejects photoelectrons from Pt(111) polarized with a degree between 10% and 40%. The spin direction coincides with a plane parallel to the surface and changes its sign when the crystal is rotated by 60\ifmmode^\circ\else\textdegree\fi{} about the surface normal.

A water-cooled mirror system for synchrotron radiation

Abstract: This paper describes the design and performance of a directly-cooled soft X-ray mirror system which has been developed at Lawrence Berkeley Laboratory for synchrotron radiation beam lines in which mirror thermal distortion must be minimized for acceptable optical performance ∗ . Two similar mirror systems are being built: the first mirror has been installed and operated at the National Synchrotron Light Source on the X-17T miniundulator beam line and will be moved to the permanent X-1 beam line when a new, more powerful undulator is installed there. The second system is being built for installation at the Stanford Synchrotron Radiation Laboratory on Beam Line VI, where the total absorbed power on the mirror may be as high as 2400 W with a peak absorbed power density of 520 W/cm2. Direct cooling by convection is achieved using internal water channels in a brazed, dispersion-strengthened copper and OFHC copper substrate with a polished electroless-nickel surface. A simple kinematic linkage and flexural pivot mounting provide for mirror positioning about two rotational axes that coincide with the optical surface. Surface figure metrology, optical configurations, and tolerancing are also discussed.

Maximum: A scanning photoelectron microscope at Aladdin

Abstract: The recent successful installation of the 30-period undulator on Aladdin, the 1 GeV electron storage ring at the Synchrotron Radiation Center of the University of Wisconsin, opens new possibilities for photoelectron spectroscopy. In particular, the high brightness of the machine, together with innovative optics, make possible the application of photoelectron spectroscopy to high-resolution soft X-ray microscopy. We call this system MAXIMUM (for Multiple Application X-ray IMaging Undulator Microscope). The proposed optical system will have a lateral resolution of better than 1000 A and a resolving power of better than 200 at 100 eV. After monochromatization, the radiation will be focused on a pinhole that can range in diameter from 1 to 100 μm, and will be prepared by lithographic techniques on a thin nickel film. The image of the pinhole, suitably demagnified, will be relayed to the sample. The image resolution and magnification can be adjusted by changing the pinhole size and the scanning step. A Schwartzschild objective can produce a demagnified image of the pinhole which is diffraction limited even at a wavelength of 40 A. At 100 A and at a numerical aperture of 0.2, the objective can produce a 250 A diameter spot. High flux will be achieved with a Mo-Si multilayer coating, for which preliminary experiments have demonstrated reflectivities near 40% at normal incidence. Other focusing elements (Fresnel zone plates and Kirkpatrick-Baez objectives) will also be implemented.

The photoelectron spectrum of HCl and DCl studied with ultraviolet excitation, high resolution x‐ray excitation, and synchrotron radiation excitation: Isotope effects on line profiles

Abstract: The HCl and DCl molecules have been studied with monochromatized x‐ray, ultraviolet, and synchrotron radiation excited photoelectron spectroscopy. Isotope effects are detected in the outer and inner valence bands using all the different excitation sources. These effects are used to describe the nature of the potential curves for the 5σ−1 state and various inner valence correlation states. The 5σ−1 state is shown to predissociate at 18.0 eV into Cl+(3P)+H(2S). The potential curves for the two outermost states in the 4σ−1 region are approximately determined. The outermost state is shown to be repulsive, whereas the second state, that corresponds mostly to the 4σ−1 single hole state, is found to be bound. One weak structure that must be associated with the 2∏ manifold of states is observed at 28.6 eV binding energy. Three structures at binding energies larger than 40 eV are reported for the first time.

Electron spin polarization analyzers for use with synchrotron radiation

Abstract: The measurement of the spin polarization of photoelectrons emitted from a magnetic material is discussed An important consideration is the acceptance phase space of the spin analyzer relative to the phase space of the photoemitted electrons to be measured Other considerations include the magnetization direction relative to the extracted beam and whether the measurements are angle integrated or angle resolved In the longitudinal geometry where the magnetization is normal to the sample surface and along the extracted photoelectron beam, conservation of canonical angular momentum adds an additional magnetic term to the beam emittance which is absent when the magnetization is in the sample plane and transverse to the extracted beam For angle resolved measurements in the transverse geometry, the advantages of a new, low-energy (∼ 100 eV) spin analyzer which is easily movable, compact and efficient are discussed Different spin analyzers are described and compared, and an analysis of their application to different spin polarized photoemission measurement configurations is given

PHOTON: A program for synchrotron radiation dose calculations

Abstract: A computer program, PHOTON, has been developed to calculate radiation levels associated with a general synchrotron beamline arrangement. PHOTON calculates the transmitted and scattered spectra as the synchrotron beam passes through sequential filters. The Compton component of this scattered radiation can then be passed through a series of materials composing a shielding wall. This radiation can then be used to calculate a dose in a medium outside of the shielding wall. Program input is such that the sequence of operations is easily followed and modified for any beamline configuration. Measurements have been performed by Brauer on existing NSLS beamlines in various geometries. Good agreement between calculated and measured dose values was found in all cases. This agreement implies that results obtained for shielding of sources containing a wide range of energies, such as that of the NSLS High Field Superconducting Wiggler, are correct.

An ultra-low emittance mode for PEP using damping wigglers

Abstract: The existing electron storage rings at Stanford University offer significant potential to produce synchrotron radiation of extremely high photon beam brightness. The facilities available now and in the near future are the storage rings SPEAR at 3.5 GeV and PEP at 15 GeV. The high brightness capabilities of the PEP ring for future experimentation as well as the potential to establish a spatially coherent X-ray source at PEP will be discussed. A mechanism based on the use of damping wigglers will be described which allows the reduction of the beam emittance far below that obtainable with other known methods.

The superconducting wiggler beamport at the National Synchrotron Light Source

Abstract: A beamport is currently being instrumented to utilize high energy synchrotron radiation from the superconducting wiggler magnet on the X-ray ring at the National Synchrotron Light Source. Two independent programs are being developed to run in tandem, nonconcurrently, on the central beamline: material sciences on X17B1 and medical research/angiography on X17B2. A high pressure research program will run independently on a side station. X17C. Considerations in the design of the beamline include handling severe power loading, radiation shielding protection and beam energy filtering.

Photoionization and Collisional Ionization of Excited Atoms using Synchrotron and Laser Radiations

Abstract: Publisher Summary This chapter presents various ionization processes such as photoionization, autoionization, and collisional ionization to be examined in excited atoms. The photon energy range from threshold to several hundred electron volts above threshold provides the most fruitful region to study these many body interactions. The information obtained from these measurements, while having great value, is somewhat restrictive because of the dipole selection rules. Only a limited class of states can be probed and the initial state is often an ensemble of nearly degenerate levels. Synchrotron radiation is a source of radiation that extends over a spectral range extending from x-rays to microwaves. Because of its intensity, synchrotron radiation is ideally suited for the observation of photoionization in gaseous samples. Most of the electrostatic interaction occurs within the core and the d wave function amplitude increases slowly with increasing radial distance. The overlap of the wave function of the excited d electron with the core is small in neon, but much larger for these other rare gases.