Showing papers on "Synchrotron radiation published in 1998"

X-ray imaging with submicrometer resolution employing transparent luminescent screens

Abstract: Microimaging techniques with synchrotron radiation demand fast, on-line x-ray detectors with a spatial resolution in the micrometer or submicrometer range. For this task an x-ray detector based on a transparent, i.e., nonscattering, luminescent screen has been developed. Its performance is described experimentally and theoretically. The detector consists of an Y3Al5O12:Ce screen, microscope optics, and a low-noise CCD camera, operated at x-ray energies between 10 and 50 keV. Good image quality is achieved if the depth of focus of the optical system is matched to the x-ray absorption length or thickness of the scintillator. A spatial resolution of 0.8 µm fwhm (1000 line pairs/mm with 10% contrast) was measured by recording the interferogram of a boron fiber. First applications in phase contrast imaging and microtomography are shown.

BeppoSAX Observations of Unprecedented Synchrotron Activity in the BL Lacertae Object Markarian 501

Abstract: The BL Lacertae object Markarian 501, one of only three extragalactic sources (with Mrk 421 and 1ES 2344+514) so far detected at TeV energies, was observed with the BeppoSAX satellite in 1997 April 7, 11, and 16 during a phase of high activity at TeV energies, as monitored with the Whipple, HEGRA, and CAT Cherenkov telescopes. Over the whole 0.1-200 keV range, the spectrum was exceptionally hard (??1, with F? ? ???), indicating that the X-ray power output peaked at (or above) ~100 keV. This represents a shift of at least 2 orders of magnitude with respect to previous observations of Mrk 501, a behavior never seen before in this or any other blazar. The overall X-ray spectrum hardens with increasing intensity, and at each epoch it is softer at larger energies. The correlated variability from soft X-rays to the TeV band points to models in which the same population of relativistic electrons produces the X-ray continuum via synchrotron radiation and the TeV emission by inverse Compton scattering of the synchrotron photons or other seed photons. For the first time in any blazar, the synchrotron power is observed to peak at hard X-ray energies. The large shift of the synchrotron peak frequency with respect to previous observations of Mrk 501 implies that intrinsic changes in the relativistic electron spectrum caused the increase in emitted power. Due to the very high electron energies, the inverse Compton process is limited by the Klein-Nishina regime. This implies a quasi-linear (as opposed to quadratic) relation of the variability amplitude in the TeV and hard X-ray ranges (for the synchrotron self-Compton model) and an increase of the inverse Compton peak frequency smaller than that of the synchrotron peak frequency.

Models of Synchrotron X-Rays from Shell Supernova Remnants

Abstract: The diffusive shock acceleration process can accelerate particles to a maximum energy depending on the shock speed and age and on any competing loss processes on the particles The shock waves of young supernova remnants can easily accelerate electrons to energies in excess of 1 TeV, where they can produce X-rays by the synchrotron process I describe a detailed calculation of the morphology and spectrum of synchrotron X-rays from supernova remnants Remnants are assumed to be spherical and in the Sedov evolutionary phase, though the results are insensitive to the detailed dynamics The upstream magnetic field is assumed uniform; downstream it is assumed to be compressed but not additionally turbulently amplified In all cases, spectra begin to depart from power laws somewhere in the optical to UV range and roll off smoothly through the X-ray band I show that simple approximations for the electron emissivity are not adequate; a full convolution of the individual electron synchrotron emissivity with a calculated electron distribution at each point in the remnant is required Models limited by the finite shock age, by synchrotron or inverse Compton losses on electrons, or by escape of electrons above some energy have characteristically different spectral shapes, but within each class, models resemble one another strongly and can be related by simple scalings The images and spectra depend primarily on the remnant age, the upstream magnetic field strength, and the level of magnetic turbulence near the shock in which the electrons scatter In addition, images depend on the viewing or aspect angle between the upstream magnetic field and the line of sight The diffusion coefficient is assumed to be proportional to particle energy (or mean free path proportional to gyroradius), but I investigate the possibility that the proportionality constant becomes much larger above some energy, corresponding to an absence of long-wavelength MHD waves Models producing similar spectra may differ significantly in morphology, which allows for possible discriminations I parameterize the model spectra in terms of a slope at 4 keV and a factor by which the X-ray flux density at that energy falls below the extrapolated radio spectrum Synchrotron radiation may contribute significantly to the X-ray emission of remnants up to several thousand years old

SPELEEM: Combining LEEM and Spectroscopic Imaging

Abstract: At present the only surface electron microscope which allows true characteristic XPEEM (photoemission electron microscopy using synchrotron radiation) and structural characterization is the spectroscopic LEEM developed at the Technical University Clausthal in the early nineties. This instrument has in the past been used mainly for LEEM studies of various surface and thin film phenomena, because it had very limited access to synchrotron radiation. Now the microscope is connected quasipermanently to the undulator beamline 6.2 at the storage ring ELETTRA, operating successfully since the end of 1996 under the name SPELEEM (Spectroscopic PhotoEmission and Low Energy Electron Microscope). The high brightness of the ELETTRA light source, together with an optimized instrument, results in a spatial resolution better than 25 nm and an energy resolution better than 0.5 eV in the XPEEM mode. The instrument can be used alternately for XPEEM, LEEM, LEED (low energy electron diffraction), MEM (mirror electron microscop...

Dose response of various radiation detectors to synchrotron radiation

Abstract: Accurate dosimetry is particularly difficult for low- to medium-energy x-rays as various interaction processes with different dependences on material properties determine the dose distribution in tissue and radiation detectors. Monoenergetic x-rays from synchrotron radiation offer the unique opportunity to study the dose response variation with photon energy of radiation detectors without the compounding effect of the spectral distribution of x-rays from conventional sources. The variation of dose response with photon energies between 10 and 99.6 keV was studied for two TLD materials (LiF:Mg, Ti and LiF:Mg, Cu, P), MOSFET semiconductors, radiographic and radiochromic film. The dose response at synchrotron radiation energies was compared with the one for several superficial/orthovoltage radiation qualities (HVL 1.4 mm Al to 4 mm Cu) and megavoltage photons from a medical linear accelerator. A calibrated parallel plate ionization chamber was taken as the reference dosimeter. The variation of response with x-ray energy was modelled using a two-component model that allows determination of the energy for maximum response as well as its magnitude. MOSFET detectors and the radiographic film were found to overrespond to low-energy x-rays by up to a factor of 7 and 12 respectively, while the radiochromic film underestimated the dose by approximately a factor of 2 at 24 keV. The TLDs showed a slight overresponse with LiF:Mg, Cu, P demonstrating better tissue equivalence than LiF:Mg, Ti (maximum deviation from water less than 25%). The results of the present study demonstrate the usefulness of monoenergetic photons for the study of the energy response of radiation detectors. The variations in energy response observed for the MOSFET detectors and GAF chromic film emphasize the need for a correction for individual dosimeters if accurate dosimetry of low- to medium-energy x-rays is attempted.

High Energy Gamma Rays from Ultrahigh Energy Cosmic Rays in Gamma Ray Bursts

Abstract: It has recently been proposed that ultrahigh energy ($\gtrsim 10^{19}$ eV) cosmic rays (UHECRs) are accelerated by the blast waves associated with GRBs. We calculate the observed synchrotron radiation spectrum from protons and energetic leptons formed in the cascades initiated by photopion production, taking into account $\gamma\gamma$ attenuation at the source. Normalizing to the emission characteristics of GRB~970508, we predict $\sim 10$ MeV - 100 GeV fluxes at a level which may have been observed with EGRET from bright GRBs, and could be detected with the proposed GLAST experiment or with ground-based air \v Cerenkov telescopes having thresholds $\lesssim $ several hundred GeV. The temporal decay of the UHECR-induced high-energy $\gamma$-ray afterglows is significantly slower than that of the lower-energy burst and associated synchrotron self-Compton (SSC) radiation, which provides a direct way to test the hadronic origin of a high-energy GRB afterglow. Besides testing the UHECR origin hypothesis, the short wavelength emission and afterglows can be used to probe the level of the diffuse intergalactic infrared radiation field or constrain redshifts of GRB sources.

The Gas Phase Photoemission Beamline at Elettra

Abstract: This paper reports the present stage of commissioning of the gas-phase photoemission beamline at Elettra, Trieste. The beamline is designed for atomic and molecular science experiments with high-resolution and high-flux synchrotron radiation. It consists of an undulator source, variable-angle spherical-grating monochromator and two experimental stations. The design value of the energy range is 20 to 800 eV with a specified resolving power of over 10000. The procedure adopted for calibration of this type of monochromator is discussed. At present a resolving power up to 20000 and a range up to 900 eV have been measured. Absorption spectra taken at the argon LII,III-edge and at the nitrogen, oxygen and neon K-edges are as sharp as, or sharper than, any reported in the literature. The instrumental broadening is well below the natural line-width making it difficult to quantify the resolution; this problem is discussed.

A determination of the spectral index of galactic synchrotron emission in the 1-10 GHz range

Abstract: We present an analysis of simultaneous multifrequency measurements of the Galactic emission in the 1-10 GHz range with 18° angular resolution taken from a high-altitude site. Our data yield a determination of the synchrotron spectral index between 1.4 and 7.5 GHz of βsyn = 2.81 ± 0.16. Combining our data with maps made by Haslam et al. and Reich & Reich, we find βsyn = 2.76 ± 0.11 in the 0.4-7.5 GHz range. These results are in agreement with the few previously published measurements. The variation of βsyn with frequency based on our results and compared with other data found in the literature suggests a steepening of the synchrotron spectrum toward high frequencies, as expected from theory because of the steepening of the parent cosmic-ray electron energy spectrum. Comparison between the Haslam data and the 19 GHz map of Cottingham also indicates a spatial variation of the spectral index on large angular scales. Additional high-quality data are necessary to provide a serious study of these effects.

Vacuum ultraviolet spectroscopy

Abstract: Synchrotron Radiation Sources Configuration of a Typical Beamline Glow Discharges and Wall Stabilized Arcs Hollow Cathode, Penning, and Electron-Beam Excitation Sources Laser Produced Plasmas Transition Radiation Vacuum Ultraviolet Lasers Radiometric Characterization of VUV Sources Imaging Properties and Aberrations of Spherical Optics and Nonspherical Optics Reflectometers Reflectance Spectra of Single Materials Polarization Optical Properties of Materials Reflecting Optics: Multilayers Zone Plates Windows and Filters Diffraction Gratings Multilayer Gratings Crystal Optics Normal-Incidence Monochromators and Spectrometers Grazing-Incidence Monochromators for Third-Generation Synchrotron Radiation Sources Spectographs and Monochromators Using Varied Line Spacing Gratings Interferometric Spectrometers Gas Detectors Photodiode Detectors Amplifying and Position Sensitive Detectors Absolute Flux Measurements Vacuum Techniques Lithography X-Ray Spectromicroscopy Optical Spectroscopy in the VUV Region Soft X-Ray Fluorescence Spectroscopy

Microscopic X-ray fluorescence analysis and related methods with laboratory and synchrotron radiation sources

Abstract: The present status of microprobe versions of XRF analysis with tube excitation and with synchrotron radiation sources is reviewed with respect to analytical parameters such as lateral resolution and imaging capability, and achievable detection limits, precision and accuracy. The main characteristics of the method are contrasted with those of other microanalytical techniques. For laboratory source µ-XRF, results with a rotating anode tube equipped with capillary X-ray optics are discussed in terms of sensitivity and achievable lateral resolution. The possibilities of the new third generation synchrotron radiation storage rings, especially those of the European Synchrotron Radiation Facility (ESRF) and its X-ray micro-fluorescence, imaging and diffraction beamline (ID 22) are discussed and related to second generation storage rings. Some characteristic applications are given to illustrate the recent possibilities of the methodologies, in particular for the characterization of atmospheric particles, and in an analytical problem related to archaeology.

A triple-crystal diffractometer for high-energy synchrotron radiation at the HASYLAB high-field wiggler beamline BW5.

Abstract: The triple-crystal diffractometer installed at HASYLAB beamline BW5 with a high-field wiggler of critical energy 27 keV for DORIS III, operated at 4.5 GeV electron energy, is described. Samples can be mounted in large cryostats or furnaces normally used in neutron scattering experiments. The instrument has been successfully applied to measure structure factors S(Q) in liquids and amorphous materials, to collect full data sets of highly accurate structure factors for charge-density work, to measure the spin component of the ground-state magnetization in transition-metal and rare-earth compounds, to study the diffuse scattering from stacking faults and dislocation loops in Si single crystals, and for the investigation of various aspects of structural phase transitions: critical scattering in SrTiO3, oxygen order and stripe order in high-To materials. A crossed-beam technique allows for local studies of texture, internal strain and phase changes in the bulk of materials.

Emission Spectra from Internal Shocks in Gamma-Ray Burst Sources

Abstract: Unsteady activity of γ-ray burst sources leads to internal shocks in their emergent relativistic wind. We study the emission spectra from such shocks, assuming that they produce a power-law distribution of relativistic electrons and possess strong magnetic fields. The synchrotron radiation emitted by the accelerated electrons is Compton upscattered multiple times by the same electrons. A substantial fraction of the scattered photons acquire high energies and produce e -->+e -->− pairs. The pairs transfer back their kinetic energy to the radiation through Compton scattering. The generic spectral signature from pair creation and multiple Compton scattering is highly sensitive to the radius at which the shock dissipation takes place and to the Lorentz factor of the wind. The entire emission spectrum extends over a wide range of photon energies, from the optical regime up to TeV energies. For reasonable values of the wind parameters, the calculated spectrum is found to be in good qualitative agreement with the observed burst spectra.

X-ray fluorescent computer tomography with synchrotron radiation

Abstract: This paper describes the possibility of a quantitative calculation of the distribution of a nonradioactive element within a selected cross section with nondestructive methods with the help of X-ray fluorescent tomography (XFCT) In order to increase measurement sensitivity, the use of a lamellar collimator was avoided One of the main problems for the quantitative determination of concentration was absorption of the stimulating synchrotron ray as well as re-absorption of the emitted fluorescent light The absorption coefficients required for a consideration of the absorption processes have been determined with two absorption tomograms The algebraic reconstruction technique (ART) and the maximum likelihood method with expectation maximization (MLEM) were used for the reconstruction of the chemical element to be classified, with close consideration of the absorption phenomenon The experiments were undertaken at the bending-magnet beamline, CEMO, at the laboratory for synchrotron radiation in Hamburg, HASYLAB (45 GeV) (100 mA) The photon intensity flux was approximately 10/sup 9/ photons/mm/sup 2//s The concentration of iodine was calculated with phantoms and an untreated, dissected human thyroid gland with the help of a calibration curve The total error related to the reconstructed mean value amounts to 20% One can find at least an iodide concentration of 06 mmol/l in this experimental setup

Momentum–space structure of relativistic runaway electrons

Abstract: The dynamics of relativistic runaway electrons in tokamak plasmas is analyzed using a test particle description that includes acceleration in the toroidal electric field, collisions with the plasma particles, and deceleration due to synchrotron radiation losses. The region of momentum space in which electron runaway takes place is determined. It is found that relativistic and synchrotron radiation effects lead to a critical electric field ER>(kTe/mec2)ED, below which no runaways are generated. In addition, the trajectories of the test electrons in momentum space show a stable equilibrium point that sets a limit on the energy that the runaway electrons can reach. Analytical expressions are given for this energy limit as a function of the toroidal electric field and plasma parameters. The dominant radiative mechanisms limiting the runaway electron energy are identified in the whole range of electric field values.

Models for X-Ray Emission from Isolated Pulsars

Abstract: A model is proposed for the observed combination of power-law and thermal X-rays from rotationally powered pulsars. For gamma-ray pulsars with accelerators very many stellar radii above the neutron star surface, 100 MeV curvature gamma-rays from e(-) or e(+) flowing starward out of such accelerators are converted to e1 pairs on closed field lines all around the star. These pairs strongly affect X-ray emission from near the star in two ways. (1) The pairs are a source of synchrotron emission immediately following their creation in regions where B approx. 10(exp 10) G. This emission, in the photon energy range 0.1 keV less than E(sub X) less than 5 MeV, has a power-law spectrum with energy index 0.5 and X-ray luminosity that depends on the back-flow current, and is typically approx. 10(exp 33) ergs/ s. (2) The pairs ultimately a cyclotron resonance "blanket" surrounding the star except for two holes along the open field line bundles which pass through it. In such a blanket the gravitational pull on e(+,-) pairs toward the star is balanced by the hugely amplified push of outflowing surface emitted X-rays wherever cyclotron resonance occurs. Because of it the neutron star is surrounded by a leaky "hohlraum" of hot blackbody radiation with two small holes, which prevents direct X-ray observation of a heated polar cap of a gamma-ray pulsar. Weakly spin modulated radiation from the blanket together with more strongly spin-modulated radiation from the holes through it would then dominate observed low energy (0.1-10 keV) emission. For non-y-ray pulsars, in which no such accelerators with their accompanying extreme relativistic back-flow toward the star are expected, optically thick e1 resonance blankets should not form (except in special cases very close to the open field line bundle). From such pulsars blackbody radiation from both the warm stellar surface and the heated polar caps should be directly observable. In these pulsars, details of the surface magnetic field evolution, especially of polar cap areas, become relevant to observations. The models are compared to X-ray data from Geminga, PSR 1055-52, PSR 0656+14, PSR 1929+10, and PSR 0950+08.

Small-angle X-ray scattering using coherent undulator radiation at the ESRF.

Abstract: A high-coherent-flux X-ray beam for small-angle-scattering studies has been produced and analyzed at the Troika beamline of the European Synchrotron Radiation Facility. The statistics of a static speckle pattern are used to characterize the coherence properties.

Internal distortion in ZrO2-CeO2 solid solutions: Neutron and high-resolution synchrotron x-ray diffraction study

Abstract: Neutron and high-resolution synchrotron x-ray diffraction measurements have indicated a tetragonal zirconia phase with both an axial ratio of unity and internal shear deformation: The oxygen displacements from ideal fluorite positions of 0.088 and 0.078 A are observed for 65 and 70 mol % CeO2–ZrO2 samples, respectively, although both c/a values are 1.000±0.001. The c/a ratio decreases with increasing of CeO2 content and decreases discontinuously to unity around a 60 mol % CeO2 composition, while the oxygen displacement decreases continuously up to about 90 mol % CeO2.

Coherent radiation of an ultrarelativistic charged particle channelled in a periodically bent crystal

Abstract: We suggest a new type of the undulator radiation which is generated by an ultrarelativistic particle channelled along a periodically bent crystallographic plane or axis. The electromagnetic radiation arises mainly due to the bending of the particle's trajectory, which follows the shape of the channel. The parameters of this undulator, which totally define the spectrum and the angular distribution of the radiation (both spontaneous and stimulated), depend on the type of the crystal and the crystallographic plane (axis), the type of projectile and its energy, and on the shape of the bent channel and, thus, can be varied significantly by varying these characteristics. As an example, we consider the acoustically induced radiation (AIR) which is generated by ultrarelativistic particles channelled in a crystal which is bent by a transverse acoustic wave. The AIR mechanism allows us to make undulators with the main parameters varying over wide ranges, which are inaccessible in the undulators based on the motion of particles in the periodic magnetic fields and also in the field of the laser radiation. The intensity of AIR can easily be made larger than the intensity of the radiation in a linear crystal and can be varied over a wide range by varying the frequency and the amplitude of the acoustic wave in the crystal. A possibility to generate stimulated emission of high-energy photons (in keV - MeV region) is also discussed.

Development of a two-dimensional imaging system for clinical applications of intravenous coronary angiography using intense synchrotron radiation produced by a multipole wiggler.

Abstract: A two-dimensional clinical intravenous coronary angiography system, comprising a large-size view area produced by asymmetrical reflection from a silicon crystal using intense synchrotron radiation from a multipole wiggler and a two-dimensional detector with an image intensifier, has been completed. An advantage of the imaging system is that two-dimensional dynamic imaging of the cardiovascular system can be achieved due to its two-dimensional radiation field. This world-first two-dimensional system has been successfully adapted to clinical applications. Details of the imaging system are described in this paper.

Ethylene on si(001)-2 1 and si(111)-7 7 : x-ray photoemission spectroscopy with synchrotron radiation

Abstract: The adsorption of ethylene on $\mathrm{Si}(001)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1$ and $\mathrm{Si}(111)\ensuremath{-}7\ifmmode\times\else\texttimes\fi{}7$ has been studied at 300 K using core-level (Si $2p,$ C $1s)$ and valence-band x-ray photoemission with synchrotron radiation. Dangling bonds play a very different role in the chemisorption process on these two surfaces. While for $\mathrm{Si}(001)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1$ the quenching of the surface states ``monitors'' the molecule uptake, this is not the case for $\mathrm{Si}(111)\ensuremath{-}7\ifmmode\times\else\texttimes\fi{}7:$ the adsorption process continues well after all surface states have disappeared, and carbon coverages greater than that deduced from the rest-atom/adatom bridge model are obtained. An alternative model is proposed, in which molecules are bonded directly to the rest plane. The thermal stability of both surfaces covered by ethylene is also studied. We relate the formation of carbon-rich layers at 820\char21{}860 K to the strong changes in the electronic structure of the silicon surface.

Very Strong TeV Emission as Gamma-Ray Burst Afterglows

Abstract: Gamma-ray bursts (GRBs) and following afterglows are considered to be produced by dissipation of kinetic energy of a relativistic fireball, and the radiation process is widely believed to be synchrotron radiation or inverse Compton scattering of electrons. We argue that the transfer of kinetic energy of ejecta into electrons may be an inefficient process and hence the total energy released by a GRB event is much larger than that emitted in soft gamma rays by a factor of ~(mp/me). We show that, in this case, very strong emission of TeV gamma rays is possible due to synchrotron radiation of protons accelerated up to ~1021 eV, which are trapped in the magnetic field of afterglow shocks and radiate their energy on an observational timescale of about a few days. This suggests the possibility that GRBs are most energetic in the TeV range, and such TeV gamma rays may be detectable from GRBs even at cosmological distances, i.e., z~1, by currently working ground-based telescopes. Furthermore, this model naturally gives a quantitative explanation for the famous long-duration GeV photons detected from GRB 940217. If TeV gamma-ray emission that is much more energetic than GRB photons is detected, it provides a strong evidence for acceleration of protons up to ~1021 eV.

Set-up and experimental parameters of the protein crystallography beamline at the Brazilian National Synchrotron Laboratory.

Abstract: The Brazilian National Synchrotron Light Laboratory (LNLS) has a dedicated protein crystallography beamline. The optical elements of the beamline include an elastically bent cylindrical mirror and a triangular bent-crystal monochromator, which focus synchrotron radiation at the position of the sample in the vertical and horizontal planes, respectively. The monochromatic radiation is tunable between 2.0 and 1.2 A with the optimum wavelengths from 1.3 to 1.6 A, chosen to maximize the photon flux from the bending magnets of the storage ring (1.37 GeV). Diffraction images are recorded on a 345 mm-diameter MarResearch image-plate detector system with on-line readout. The experimental parameters of the beamline, such as the integral monochromatic flux and focus size, have been measured. The size of the beam at the position of the focal point is 0.5 x 0.5 mm(2). The flux density is between 4.4 x 10(10) and 8 x 10(10) photons s(-1) mm(-2) for wavelengths from 1.28 to 1.6 A. The energy resolution is sufficient to measure absorption edges of elements between 1.28 and 2 A. The facility, intended to serve the national and international community, has been commissioned and is available for users.

Evaluation of Residual Stresses in the Bulk of Materials by High Energy Synchrotron Diffraction

Abstract: High energy synchrotron diffraction is introduced as a new method for residual stress analysis in the bulk of materials. It is shown that energy dispersive measurements are sufficiently precise so that strains as small 10−4 can be determined reliably. Due to the high intensity and the high parallelism of the high energy synchrotron radiation the sample gauge volume can be reduced to approximately 50 μm×1 mm×1 mm compared to gauge volume of one mm3 up to several mm3 achievable by neutron diffraction. The benefits of the high penetration depth and the small gauge volume are demonstrated by the results of stress studies performed on a fiber reinforced ceramic, a functional gradient material and a metal-ceramic compound. Furthermore, it is shown that in case of a cold extruded metal specimen the energy dispersive measurement technique yields simultaneous information about texture and residual stresses and thus allows a detailed investigation of elastic and plastic deformation gradients.

Thermalization by synchrotron absorption in compact sources: electron and photon distributions

Abstract: The high-energy continuum in Seyfert galaxies and galactic black hole candidates is likely to be produced by a thermal plasma. There are difficulties in understanding what can keep the plasma thermal, especially during fast variations of the emitted flux. Particle–particle collisions are too inefficient in hot and rarefied plasmas, and a faster process is called for. We show that cyclo-synchrotron absorption can be such a process: mildly relativistic electrons thermalize in a few synchrotron cooling times by emitting and absorbing cyclo-synchrotron photons. The resulting equilibrium function is Maxwellian at low energies, with a high-energy tail when Compton cooling is important. Assuming that electrons emit completely self-absorbed synchrotron radiation and at the same time Compton scatter their own cyclo-synchrotron radiation and ambient UV photons, we calculate the time-dependent behaviour of the electron distribution function, and the final radiation spectra. In some cases, the 2–10 keV spectra are found to be dominated by the thermal synchrotron self-Compton process rather than by thermal Comptonization of UV disc radiation.

W/C, W/Ti, Ni/Ti, and Ni/V multilayers for the soft-x-ray range: experimental investigation with synchrotron radiation

Abstract: An experimental investigation of W/C, W/Ti, Ni/Ti, and Ni/V multilayers is presented that uses synchrotron radiation in the soft-x-ray energy region between 100 and 1500 eV with special emphasison the water window. The multilayers were designed as normal incidence reflectors and for polarimetry purposes around the Brewster angle. Both reflection and transmission multilayers were prepared for use as linear polarizers and phase retarders, respectively, to produce or analyze circularly polarized light. Their period was optimized to achieve maximum reflectance at the 1s absorption edge of C (284 eV) and the 2p edges of Ti (454 eV) and V (512 eV), respectively. At these edges the multilayers show an enhancement of reflectance and energy resolution that is in accordance with theoretical calculations.

Microfabrication using synchrotron radiation

Abstract: The realization of precision deep microstructures requires high-energy, intense parallel beams of x-rays from synchrotron radiation sources and novel process technology. Deep x-ray lithography with synchrotron radiation is basically a shadow printing process in which a two-dimensional pattern is accurately transferred from a mask into a resist material by chemical changes induced by the radiation. Subsequent electroforming and moulding processes are used to manufacture microstructures from metals, plastics and ceramics. This process, known as LIGA (LIthographie, Galvanoformung, and Abformung), first developed in Germany, is based on a combination of lithography, electroforming and replication processes. The development of the LIGA process for the fabrication of a wide range of precision microstructures has been stimulated by the increasing use of synchrotron radiation sources for lithography. Applications for microstructures exist in many sectors of industry. These include chemical and process engineering, biomedical instrumentation, automotive and aerospace technology, environmental monitoring and information technology. Emphasis is placed on three main areas, micromechanics, micro-optics and microfluidics, which are emerging with the widest range of industrial applications. This paper reviews the progress being made in microfabrication technology using x-ray beam lithography and the LIGA process. It includes a description of synchrotron radiation, storage ring sources, the fabrication processes, applications and potential markets. Reference is also made to European networks and R&D activity worldwide.

Nonthermal Origin of X-Rays from Rotation-powered Neutron Stars

Abstract: We propose that the bulk of X-rays observed in pulsars results from the synchrotron radiation of e± pairs created in strong pulsar magnetic field near the neutron star surface by curvature photons emitted by charged particles on their way from the outer gap to the neutron star surface. The characteristic energy of these curvature photons is completely determined by the size of the outer gap, which is self-consistently limited by thermal X-rays from the neutron star surface heated by the backflow electrons/positrons from the outer gap. It is this limitation of the outer gap size (potential drop) that constrains the luminosity LX of the synchrotron X-rays emitted by a pulsar to about 0.1% of its spin-down power Lsd.

A fast detector using stacked avalanche photodiodes for x-ray diffraction experiments with synchrotron radiation

Abstract: We have developed a fast detector using stacked avalanche photodiodes (APDs) for x-ray diffraction experiments with synchrotron radiation. This detector has four independent channels of APDs, and the detector efficiency has reached 55% in all for 16.53 keV x rays. Since the dead time of the counting system is shorter than 4 ns, output rates of up to 4.5×108 counts/s have been obtained for 16.53 keV x rays. The dynamic range is more than 1010 in the multibunch mode of a storage ring. Pulse-height measurements at output rates of up to 108 counts/s were successfully carried out by sequential single-channel discrimination.