Showing papers on "Synchrotron radiation published in 1982"
TL;DR: In this article, the development of pair photon cascades initiated by high energy electrons above a pulsar polar cap is simulated numerically using the energy of the primary electron, the magnetic field strength and the period of rotation as parameters and follows the curvature radiation emitted by the primary, the conversion of this radiation e(+) - e(-) pairs in the intense fields, and the quantized synchrotron radiation by the secondary pairs.
Abstract: The development of pair photon cascades initiated by high energy electrons above a pulsar polar cap is simulated numerically. The calculation uses the energy of the primary electron, the magnetic field strength, and the period of rotation as parameters and follows the curvature radiation emitted by the primary, the conversion of this radiation e(+) - e(-) pairs in the intense fields, and the quantized synchrotron radiation by the secondary pairs. A recursive technique allows the tracing of an indefinite number of generations using a Monte Carlo method. Gamma ray and pair spectra are calculated for cascades in different parts of the polar cap and with different acceleration models. It is found that synchrotron radiation from secondary pairs makes an important contribution to the gamma ray spectrum above 25 MeV, and that the final gamma ray and pair spectra are insensitive to the height of the accelerating region, as long as the acceleration of the primary electrons is not limited by radiation reaction.
406 citations
TL;DR: In this article, an optimal focussing kinematically simple two-element optics for plane grating monochromators is described, which is used to monochromeise synchrotron radiation in the soft X-ray region.
231 citations
TL;DR: In this paper, x-ray diffraction measurements of lattice strain in silicon during pulsed-laser annealing have been made with nanosecond resolution by using synchrotron radiation.
Abstract: Time-resolved x-ray diffraction measurements of lattice strain in silicon during pulsed-laser annealing have been made with nanosecond resolution by using synchrotron radiation. Analyses of the strain in pure and boron-implanted silicon in terms of temperature indicate high temperatures and evidence for near-surface melting, in qualitative agreement with the melting model of laser annealing.
137 citations
TL;DR: In this article, angle resolved photoemission using synchrotron radiation was employed to elucidate the molecular structure of the species present in the low and high temperature phases of ethylene and acetylene on Pt(111).
99 citations
TL;DR: In this article, a discussion is given of principles and applications of surface extended X-ray absorption fine structure (SEXAFS) measurements of chemisorbed atoms on surfaces.
74 citations
TL;DR: In this paper, the design and operation of a focusing camera for high-resolution macromolecular crystallography with synchrotron radiation (SR) are described and evaluated on the basis of five years of use.
Abstract: The design and operation of a focusing camera for high-resolution macromolecular crystallography with synchrotron radiation (SR) are described. The performance of this service-oriented instrument is evaluated on the basis of five years of use. Standard procedures for data collection, data processing and data reduction have been modified to take unusual features of the SR source into account; the effect of polarization is thoroughly discussed.
69 citations
TL;DR: In this article, a Schwartzchild black hole is studied numerically and analytically for a range of hole masses and accretion rates in which synchrotron emission is the dominant radiative mechanism.
Abstract: Spherical accretion onto a Schwartzchild black hole, of gas with frozen-in magnetic field, is studied numerically and analytically for a range of hole masses and accretion rates in which synchrotron emission is the dominant radiative mechanism. At small radii the equipartition of magnetic, kinetic, and gravitational energy is assumed to apply, and the gas is heated by dissipation of infalling magnetic energy, turbulent energy, etc. The models can be classified into three types: (a) synchrotron cooling negligible, (b) synchrotron cooling important but synchrotron self-absorption negligible, (c) synchrotron cooling and self-absorption important. In the first case gas temperatures become very high near the horizon but luminosity efficiencies (luminosity/mass-energy accretion rate) are low. In cases (b) and (c) the gas flow near the horizon is essentially isothermal and luminosity efficiencies are fairly high. The analysis and results for the isothermal cases (b) and (c) are valid only for moderate dissipative heating and synchrotron self-absorption. If self-absorption is very strong or if dissipated energy is comparable to infall energy, Comptonization effects, not included in the analysis, become important.
56 citations
TL;DR: The application of synchrotron radiation from high energy electron storage rings as an excitation source for X-ray fluorescence analysis of trace elements will greatly extend the sensitivity of the fluorescence technique.
56 citations
TL;DR: In this article, partial cross section and asymmetry parameters of the 2B1, 2A1, and 2B2 ionic states of H2O+ have been measured at photon energies of 18-31 eV, by time-of-flight photoelectron spectroscopy using synchrotron radiation.
Abstract: The partial cross section and asymmetry parameters of the 2B1, 2A1, and 2B2 ionic states of H2O+ have been measured at photon energies of 18–31 eV, by time‐of‐flight photoelectron spectroscopy using synchrotron radiation. The atomic character of the molecular orbitals is discussed in the interpretation of similarities and differences between the measurements for these states. Other synchrotron radiation data, resonance line measurements, and (e, 2e) dipole results are included. A multiple‐scattering Xα (MSXα) calculation and a ground‐state inversion method calculation are in good agreement with our cross section measurements. There is excellent agreement between experimental asymmetry parameters and those computed from the MSXα method. Stieltjes–Tchebycheff imaging model calculations suggest the presence of resonant channels. This may be the origin of weak resonance structure present in the measurements.
54 citations
01 Jan 1982
53 citations
CERN1
TL;DR: In this article, general theoretical considerations on diffraction and depth of field phenomena involved in the different cases of radiation by relativistic particles in magnetic fields: undulator, synchrotron, and short magnet radiation, and their effects on beam profile image formation are examined.
TL;DR: Using both synchrotron and HeII radiation, the electronic and geometric structure of Pt{110}-(2×1)p1g1 CO was examined as discussed by the authors, and shape resonance for the 4σ orbital of CO was found to be peaked at 38 eV, while that for the 5σ orbital is peaked at 28 eV No shape resonance is observed from the 1π orbital.
01 Oct 1982
TL;DR: In this article, the beamline and spectrometer instrumentation for high-resolution X-ray scattering at the Stanford Synchrotron Radiation Laboratory is described, and the combination of photon intensity at the sample of ∼ 1013 photons/s 10 mm2 and the momentum transfer resolution of ΔQ ∼ 10 −4 A −1 make this a unique facility.
Abstract: Beamline and spectrometer instrumentation for high-resolution X-ray scattering at the Stanford Synchrotron Radiation Laboratory is described. The combination of photon intensity at the sample of ∼ 1013 photons/s 10 mm2 and the momentum transfer resolution of ΔQ ∼ 10 −4 A −1 make this a unique facility. Examples are given of data obtained on two-dimensional phase transitions both in studies of thin (2 molecular layers) liquid crystal films and rare gas monolayers on pyrolytic graphite substrates.
TL;DR: In this paper, it was pointed out that electron storage rings, in addition to their intended purpose and their secondary use as intense sources of x rays, might also serve as pulsar simulators, producing a similar spectrum of coherent emission, the properties and modification of which could be studied in the laboratory.
Abstract: Energetic electron bunches in storage rings produce pulsed bursts of incoherent synchrotron radiation. It is pointed out that they should also produce a roughly comparable power output of coherent radio-frequency radiation. Thus electron storage rings, in addition to their intended purpose and their secondary use as intense sources of x rays, might additionally serve as pulsar simulators, producing a similar spectrum of coherent emission, the properties and modification of which could be studied in the laboratory. A spontaneous bunching of electrons (artificially bunched here) might be evidenced as ''superbunching.''
TL;DR: In this article, it is shown that it is possible to phase the X-ray reflections from a macromolecular crystal which contains one heavy atom per molecule without having recourse to the conventional method of multiple isomorphous replacement, by making use of anomalous dispersion effects alone.
Abstract: In principle, it is possible to phase the X-ray reflections from a macromolecular crystal which contains one heavy atom per molecule, without having recourse to the conventional method of multiple isomorphous replacement, by making use of anomalous dispersion effects alone1. To do this, it is necessary to measure each reflection over a narrow range of wavelengths centred on an absorption edge of the heavy atom, where f′ and f″, the real and imaginary anomalous components of the scattering factor, are varying rapidly. The availability of powerful synchrotron radiation sources with a continuous energy spectrum has stimulated interest in such phasing methods, but previously experiments1 have been limited to making measurements on only one reflection at a time and/or to measuring at only a few discrete wavelengths near the absorption edge. We are developing a method at the Daresbury Synchrotron Radiation Source (SRS) which produces an energy profile along an axis of each and every diffraction spot in a screenless oscillation photograph. We show here that the approach is feasible using a single crystal o heptahydrido bis (diisopropylphenyl)phosphine rhenium using the LIII absorption edge of rhenium at a wavelength of 1.1772 A.
TL;DR: In this article, a fish-scale wall that preferentially reflects radiation propagating in one direction while absorbing that going oppositely is proposed to transfer momentum to the electrons through radiation pressure, and a rough theoretical treatment shows that at high temperatures (30-50 keV) sufficient current for a steady state tokamak may be driven.
Abstract: A tokamak at fusion temperatures generates large amounts of synchrotron radiation. With proper configuration of the walls, this radiation can sustain the current. This is accomplished by a fish-scale wall that preferentially reflects radiation propagating in one direction while absorbing that going oppositely. The wall transfers momentum to the electrons through radiation pressure. A rough theoretical treatment shows that at high temperatures (30-50 keV) sufficient current for a steady-state tokamak may be driven.
TL;DR: In this article, a simple calculation is made of the electromagnetic field radiated due to a charged particle traversing a plate of chiral material, and the transition radiation from this chiral plate is round to differ from the usual dielectrie transition radiation.
Abstract: A simple calculation is made of the electromagnetic field radiated due to a charged particle traversing a plate of chiral material. The transition radiation from this chiral plate is round to differ from the usual dielectrie transition radiation. Discussion is presented placing in evidence the characteristics of the radiation and comments are made concerning the possible applicability of the transition radiation mechanism.
TL;DR: In this paper, the problem of radiation of relativistic charged particles in matter is considered from a unified point of view for an amorphous medium and for a single crystal.
Abstract: The review treats the problem of radiation of relativistic charged particles in matter. The radiation of fast particles in an external field is considered from a unified point of view for an amorphous medium and for a single crystal. The basic attention is paid to the process of radiation in a single crystal where an enhancement of the radiation occurs as compared with an amorphous medium. This effect is shown to be due to the coherent and the interference mechanisms of radiation of relativistic particles in single crystals. First we outline the Born theory (quantum and classical) of coherent radiation of fast particles and show that this theory is valid if the particle propagates through the crystal far from the directions of channeling and if the scattering angle of the particle is small compared with the typical radiation angle of a relativistic particle. Then we show that a violation of these conditions leads to new effects in radiation such as, e.g., the effect of intense radiation of superbarrier and channeled particles, and the effect of suppression of coherent radiation. The comparison of theoretical and experimental results confirms the existence of new effects in the radiation. In conclusion, we review briefly new physical effects that must take place in single crystals at high energies in several other electrodynamical processes.
TL;DR: In this article, it was shown that the free-free interpretation of most γ-ray bursts with magnetic field B ≳ 1012 G is not sufficient for the case of neutron stars.
Abstract: The reported continuum spectra (∼20 keV–2 MeV) of most γ-ray bursts resemble a simple exponential1–4. Hence, the conventional view is that they are the optically thin free–free (bremstralung) emission of a hot thermal plasma (kT ≳ 100 keV with the exception of a few soft events, notably the 5 March 1979 event). I show here that: (1) independent of the source distance, there is an inherent difficulty with the free–free interpretation if the sources are indeed neutron stars with magnetic field B ≳ 1012 G, because the synchrotron emissivity of these hot thermal electrons would greatly exceed then free–free emissivity for any reasonable electron density consistent with τes ≪ 1 required by observations; (2) the spectral data can be fitted equally well, if not better, by optically thin thermal synchrotron spectra of mildly relativistic (kT ∼ mc2) electrons; (3) the absence of observable low-energy turnover due to synchrotron self-absorption (or high energy Compton distortion) puts interesting upper limits to the source of luminosity and distance. Most sources are noncosmological (<10 kpc–1 Mpc) but not necessarily as nearby as some authors have suggested using the free–free spectral interpretation (see, for example, ref. 2).
TL;DR: The anomalous scattering terms f′ and f′′ for Gd and Sm near their L3 absorption edges, measured in diffraction experiments with synchrotron radiation more nearly monochromatic than the natural level widths, show even larger effects than earlier measurements with a larger X-ray bandwidth as mentioned in this paper.
Abstract: The anomalous scattering terms f′ and f′′ for Gd and Sm near their L3 absorption edges, measured in diffraction experiments with synchrotron radiation more nearly monochromatic than the natural level widths, show even larger effects than earlier measurements with a larger X-ray bandwidth. A test of angular dependence shows f′ for Sm to decrease in magnitude with increasing diffraction angle, while f′′ is essentially constant.
TL;DR: Several mechanisms for emission of electromagnetic radiation by relativistic electrons in various media which are of interest for generating intense ultraviolet, x-ray, and γ radiation are examined in this paper.
Abstract: Several mechanisms for emission of electromagnetic radiation by relativistic electrons in various media which are of interest for generating intense ultraviolet, x-ray, and γ radiation are examined. Theoretical and experimental results on ultraviolet and x-ray Cherenkov radiation, quasi-Cherenkov radiation in artificial periodic structures, radiation from crystals which results from the diffraction of virtual photons, and radiation accompanying channeling are discussed.
Journal Article•
TL;DR: In this paper, the wavelength-resolved luminescence decays of the very weak emission from DNA and of some components at room temperature have been investigated by using the LURE synchrotron source with a spectrophotofluorometer using a fast single photon counting detection.
TL;DR: In this paper, the authors developed a model to describe the transport of polarized synchrotron radiation in an optically thin source possessing small amplitude fluctuations in thermal electron density, energetic electron density and vector magnetic field.
Abstract: We have developed a model to describe the transport of polarized synchrotron radiation in an optically thin source possessing small amplitude fluctuations in thermal electron density, energetic electron density, and vector magnetic field. The analysis employs an approximation termed the small phase approximation, which is similar to the first order Rytov approximation in the theory of wave propagation in a random medium. Expressions are derived relating the (observable) autocorreltions and cross-correlations of the Stokes parameters Q and U to the correlation functions of the aforementioned physical quantities. The last section of the paper is intended for observers, and describes how data from polarization maps may be used to determine the intensity and spectral characteristics of turbulence in a synchrotron source, such as a radio galaxy.
TL;DR: In this paper, the absolute intensity and the circular polarization of the synchrotron radiation with a bandwidth of 0.05 nm has been experimentally determined to be between 10 9 and 10 10 photons s −1 and (83±3)%, respectively.
TL;DR: In this paper, the capabilities of synchrotron radiation excitation for the analysis of low-concentration ''thin'' samples of elements spanning much of the periodic table are defined.
Abstract: This chapter reports on the first part of a program to define the capabilities of synchrotron radiation (SR) excitation for the analysis of low-concentration ''thin'' samples of elements spanning much of the periodic table. It attempts to synopsize the available data and to compare results obtained by alternative methods of x-ray analysis. It discusses the production of SR and the experimental setup, demonstrates the capability of continuum SR as a primary source for XRF, and finds that the experimental minimum detection limits (MDL), determined with a very simple experimental configuration, fell in the 1-100 pg range and agree satisfactorily with predictions.