Showing papers on "Synchrotron radiation published in 1975"

Atomic inner-shell processes

Abstract: : X-Ray and Auger transition probabilities were calculated for atoms that have been singly and multiply ionized in inner shells. The effects of relativity and configuration interaction on these rates were studied, and lifetimes of atomic inner-shell holes were computed. Synchrotron radiation was employed for precision measurements of atomic level energies, for the study of inelastic scattering, and for the investigation of sub-threshold excitation of atomic hole states. (Author)

On the Pulsar Emission Mechanisms

Abstract: A review of pulsar-emission mechanisms is presented. Topics discussed include the pulsar magnetosphere, mechanisms of electromagnetic radiation, formation of the radiation polar diagram, mechanisms of pulsars' radio emission, and mechanism of optical, x-ray and gamma-ray emission of the pulsar in the Crab.

Gamma ray astrophysics

Abstract: Gamma ray production processes are reviewed, including Compton scattering, synchrotron radiation, bremsstrahlung interactions, meson decay, nucleon-antinucleon annihilations, and pion production. Gamma ray absorption mechanisms through interactions with radiation and with matter are discussed, along with redshifts and gamma ray fluxes.

Gravitational Perturbation Theory and Synchrotron Radiation

Abstract: Focussing mechanisms for gravitational radiation.- Relativistic geodesics.- Ordinary synchrotron radiation.- Perturbations of spacetimes.- Decoupled & separated perturbation equations.- Polarization.- Geodesic synchrotron radiation.- Discussion.

Synchrotron radiation – its application to high‐speed, high‐resolution X‐ray diffraction topography

Abstract: With almost perfect silicon crystals and cleaved lithium fluoride crystals as extreme examples, the feasibility of using synchrotron radiation for X-ray diffraction topography has been investigated. In both spatial resolution and strain resolution the synchrotron source diffraction topographs are competitive with topographs obtained using conventional X-ray sources but exposure times are reduced from several hours per cm2 to one second per cm2 using standard recording techniques with Ilford nuclear emulsions. Contrary to (the author's) expectations, the instrumentation required is far simpler for synchrotron radiation than for conventional sources.

Preliminary Design of a Dedicated Synchrotron Radiation Facility

Abstract: An electron storage ring to be used solely as a synchrotron radiation source has been designed for a maximum energy of 1.5 GeV, expandable to 2 GeV, and a maximum current of 1 A, High field superconducting magnet wigglers to serve as hard radiation ports have been incorporated into the ring to make available a wide range of wavelengths for simultaneous experiments. The regular lattice consists of a series of small achromatic bends forming the arcs. The wiggler magnets are placed in low-s in the center of insertions separating these arcs. The arrangement minimizes the electron emittances and yields high source brightness. Other machine parameters are dictated by experimental requirements and apparatus as well as by cost constraints.

Photoelectron spectroscopy by time-of-flight technique using synchrotron radiation

Abstract: A time−of−flight spectrometer for photoelectron spectroscopy is described. It is based on the pulsed structure of the synchrotron radiation emitted from the storage ring (SPEAR) at SLAC with a pulse width of 1.5 nsec and a repetition period of 780 nsec. The sample is irradiated with monochromatic light from a soft x−ray grazing incidence monochromator which works in the photon energy range of 25−1500 eV. The time−of−flight spectrometer consists of a 6 in. mu−metal drift tube which can be pivoted around the sample making angularly resolved photoelectron spectroscopy feasible in both the horizontal and vertical direction. On the sample side of the drift tube a retardation sector is attached and on the other side, a fast channelplate detector. The design parameters are 100 MeV energy resolution at 5 eV at 1° angular resolution. Some preliminary results on single crystals are described.

An electron synchrotron maser based on an intense relativistic electron beam

Abstract: An electron cyclotron maser has been operated with an output of ∼50 MW of coherent radiation at a frequency ∼8 GHz. A magnetic field configuration is described which effectively converts streaming electron energy into energy transverse to the streaming direction. The redistribution of beam energy makes available a source of free energy to be converted, via an instability, into radiation at the Doppler‐shifted relativistic electron cyclotron frequency. A nonlinear theoretical analysis shows that the coherent synchrotron radiation is a relativistic negative mass type instability reflecting the fact that the cyclotron frequency is a function of the electron energy. The emission was narrow band with a coherence time ≳50 nsec, and was also spatially coherent being primarily radiated into the TE01 circular waveguide mode. The potential for making a frequency tunable maser by employing a tapered drift tube has also been demonstrated.

Energy loss of relativistic electrons and positrons traversing cosmic matter

Abstract: Questions of adiabatic expansion are considered along with aspects of Compton scattering, bremsstrahlung, electronic excitation, synchrotron radiation, and electron-positron pair production. It is found that, unless the intergalactic magnetic field is very small, synchrotron radiation will dominate all other energy loss processes at ultrahigh electron and positron energies. The dependence of the loss rates on the cosmic epoch is also discussed.

X-ray photolithography

Abstract: Photolithography of microcircuits with elements in the micrometer size range is performed with X-ray exposure of photoresist layers through electron beam generated shadow masks. Synchrotron radiation from a particle accelerator is used as an intense source of well collimated X-rays and Bragg reflection from a mosaic crystal is used to provide spectral purity for good contrast in the exposed photoresist pattern.

Absolute radiometric calibration of detectors between 200-600 A

Abstract: Radiometric transfer standards consisting of windowless diodes with cathodes made of anodized aluminum oxide on aluminum are now available from the National Bureau of Standards with calibrations in the 200-600-A wavelength range. This extends the previously existing range of calibration for these diodes (600-1200 A). For wavelengths shorter than 600 A, synchrotron radiation at NBS-SURF is used as the source of radiant energy. A noble gas double ionization chamber is used to calibrate a secondary standard diode that is then intercompared with the transfer standards. Monitors take into account variations in the intensity of synchrotron radiation and in beam position. Methods of accounting for the effects of second-order radiation in the incident flux and secondary ionization in the double ionization chamber are discussed. Calibration uncertainties are about 10%.

Electroreflectance of GaAs and GaP to 27 eV using synchrotron radiation

Abstract: Electroreflectrance (ER) spectra of GaAs and GaP, taken with the Schottky-barrier method, exhibit to 27 eV the strong structural enchancement and high resolution characteristic of similar measurements below 6 eV. Above 20 eV, a new set of critical points is observed between the flat valence bands derived from the Ga 3d core levels and the local extrema of the sp3 conduction bands. The attained resolution, of the order of 100 meV, enables us to resolve clearly the spin-orbit splitting of 0.45 eV of the 3d-derived valence bands. The following critical-point energies have been determined in GaAs and GaP, respectively. sp3 valence conduction: E1′, 6.63 ± 0.05 eV, and 6.80 ± 0.05 eV; E1′+Δ1′, 6.97 ± 0.05 eV (GaAs only); E0''(Γv15→Γc12), 10.53 eV, and 9.38 ± 0.1 eV; E0'''(Γv15→Γc1), 8.33 ± 0.1 eV, and 10.27 ± 0.1 eV, E1'', 9.5 ± 0.2 eV, and 10.7 ± 0.2 eV. E5, E6, and E7 structures are observed at 15.1, 16.7, and 17.9 eV in GaAs, and at 14.7, 16.1, and 18.6 eV in GaP. Relative values of 3d core to sp3 conduction-band matrix elements are estimated for several states and show that the lowest 3d core-level ER structures arise from transitions terminating at the Xc1conductionband minimum. We calculate an exciton or core-hole interaction shift of 150 meV for GaP and 200 meV for GaAs, which indicates that core-hole effects are probably small for these materials. Spectral features with initial structure less than 100 meV in width are observed above 20 eV, showing that broadening effects are much smaller in this energy range than previously believed.

The Use of Synchrotron Radiation as an Absolute Source of VUV Radiation.

Abstract: Synchrotron radiation has been used as a standard source to calibrate spectrographic instruments at the National Bureau of Standards (NBS). Conceptually it is straightforward to apply the calculable continuum distribution of synchrotron radiation to problems requiring a source of known irradiance if the electron energy, the radius of the electron orbit, and the beam current are known. In practice many factors affect the accuracy of such a calibration, such as temporal and spatial variations in the electron beam, uncertainties in the orbital radius and maximum energy of the orbiting electron beam. These sources of error are discussed and the method of calibration on SURF-I is specified. A storage ring synchrotron radiation facility (SURF-II) is now operational at NBS. The calibration techniques developed for SURF-I are applied to SURF-II with anticipated improvements in calibration accuracy. For SURF-I the incident flux was determined with an accuracy of 15 percent while for SURF-II we anticipate accuracies of about 7 percent.

Synchrotron radiation as a new tool within photon‐beam technology

Abstract: Synchrotron radiation is now playing an increasingly important role in recent developments of new light sources. Synchrotron light emitted from a relativistic electron beam has a radiation pattern which makes it a unique source. The advantages with this type of radiation can be summarized as (a) continuous spectrum extending from the ir to the x‐ray region, (b) strongly polarized, (c) highly collimated, (d) pulsed structure allowing time‐resolution spectroscopy, and (e) high intensity making feasible the use of monochromators with narrow band pass. The Stanford Synchrotron Radiation Project has been in operation since May 1974 as a U.S. National Facility for uv and x‐ray research in many disciplines using the radiation from the storage ring SPEAR at the Stanford Linear Accelerator Center. The radiation spectrum is characterized by the critical energy which varies as E3 (E=electron‐beam energy) and is 11 keV for E=4 GeV. Useful flux is available out for approximately five times the critical energy. Five mo...

Wave zone structure of NP 0532 and infrared radiation excess of Crab Nebula

Abstract: At the distancer≳1015 cm from NP 0532 the plasma concentration decreases so that the intense low-frequency wave (ν=30 Hz) can propagate. The interaction of this wave with the electrons ejected from the pulsar should result in the IR radiation withFν∼102 fu at λ∼10 μ. This flux is the order of the excess IR radiation from the Crab Nebula.

The use of synchrotron radiation for X-ray topography of phase transitions

Abstract: The use of synchrotron radiation for X-ray topography of phase transitions is described, using crystals of barium titanate. Several topographs are obtained simultaneously with an exposure time between 15 and 30 sec, thus obviating the need for elaborate temperature control. The technique is rapid and requires very little equipment.

X-ray absorption spectroscopy using synchrotron radiation for structural investigation of organometallic molecules of biological interest.

Abstract: The technique of x-ray absorption spectroscopy using tuneable, very intense x-rays from a high energy electron storage ring has been applied to study of the estended x-ray absorption fine structure for Cu and Ni tetraphenylporphyrin and methemoglobin. Preliminary analysis shows that the spectra may be interpreted as a super-position of modulations arising from the nearest neighbor nitrogen and pyrrole alpha-carbon coordination sheels of the metal atoms. We estimate that with the observed magnitude of noise to modulation amplitude, relative shifts of 0,5% in the metal-nitrogen to metal-carbon bond distances in the prophyrins should be observable using extended x-ray absorption fine structure and that this technique may provide a method of observing these types of structural changes in solution.

Transition Radiation from Ultrarelativistic Particles

Abstract: In the present paper, we give a simple derivation of the spectrum and angular distribution of the transition radiation emitted by ultrarelativistic particles which pass through dielectric foils. The approximations appropriate for high-frequency radiation in the ultrarelativistic limit are made at the beginning. The calculations are consequently much simpler than standard calculations, and our results, some of which are apparently new, are relatively simple and easy to interpret. The primary emphasis in the development is on conditions likely to be encountered in the application of transition radiation detectors in high-energy physics.

Unfolding first and second order diffracted radiation when using synchrotron radiation sources: a technique.

Abstract: A technique is presented of using a single calibrated XUV detector for radiometric measurements of synchrotron radiation after the radiation passes through a monochromator that produces a mixture of first and second order diffracted radiation. Irradiance measurements are made with the synchrotron source operating at two different energies for the orbiting electrons. The known change in the spectral distribution produced by the electron energy change is used to calculate the flux in both first and second order. The dependence of the precision of these determinations on the two detected currents and on the detector calibration at both first and second order wavelengths is calculated. Experimental results using the National Bureau of Standards synchrotron (SURF-I) are presented, and anticipated results for the new NBS electron storage ring (SURF-II) are calculated.

Optical radiation from the Crab pulsar

Abstract: Possible mechanisms for producing the optical radiation from the Crab pulsar are proposed and discussed. There are severe difficulties in interpreting the radiation as being produced by an incoherent process, whether it be synchrotron radiation, inverse-Compton radiation or curvature radiation. It is proposed therefore that radiation in the optical part of the spectrum is coherent. In the polar cap model, a small bunch of electrons and positrons forms near each primary electron as a result of the pair-production cascade process. Ambient electric fields give rise to energy separation, as a result of which either the electrons or positrons will dominate the radiation from each bunch. The roll-off in the infrared is ascribed to synchrotron absorption by electrons and positrons located between the surface of the star and the force-balance radius. Various consequences of this model, which may be subjected to observational test, are discussed.

The Spectrum of Cosmic Electrons with Energies between 6 and 100 GeV

Abstract: This experiment was carried out during three balloon flights which provided a total exposure of 3500 + or - 60 sq m sec sterad at an average depth of 4.8 g/sq cm The detector, in which the development of cascade showers in a 33.7 rl absorber was sampled by 10 scintillation counters and 216 Geiger-Muller tubes, was calibrated at the Cornell Electron Synchrotron, the separation of cosmic electrons from the nuclear background was confirmed by extensive analysis of data from the flights, from the calibration and from ground level exposure. The spectral intensity of primary cosmic ray electrons were found in particles/sq m sec sterad GeV. Similarly, the ground level spectrum of secondary cosmic ray electrons was also found. The steepness of the spectrum of cosmic electrons relative to that of nuclei implies one of the following conclusions: either the injection spectrum of electrons is steeper than that of nuclei, or the electron spectrum has been steepened by Compton/synchrotron losses in the energy range covered by the experiment.

An interpretation of the radio outbursts of Cygnus X-3.

Abstract: We describe the radio bursts from Cyg X-3 by an expanding cloud of relativistic particles and magnetic fields that is uniformly mixed with an ionized thermal gas. We follow the time evolution of the synchroton radiation from such a cloud including both synchrotron losses and adiabatic losses in the calculation. In the immediate postmaximum period, synchrotron losses dominate and determine the character of the subsequent decay of the burst; this is reflected in an exponential form of the decay near maximum. At later times, adiabatic losses are more important and the later stages of the decay follow a power law; this behavior is in keeping with the observations. The coexpansive thermal gas attenuates the low-frequency radio spectrum via free-free absorption, a process which effectively competes with synchroton self-absorption in determining the optical depth at all frequencies. The agreement obtained with this model between the observed and calculated radio bursts is very satisfactory. (AIP)

On the production of power-law spectra and the evolution of cosmic synchrotron sources: a model for the Crab nebula.

Abstract: New solutions of the energy diffusion equation for ultrarelativistic electrons undergoing Fermi acceleration are investigated. Two special cases are considered, which produce power-law electron spectra in a natural way, and which are applicable to models of expanding synchrotron sources. These are applied to the Crab Nebula, where Fermi acceleration seems necessary to provide electrons energetic enough to produce the observed nebular X-rays. Curvature radiation losses prevent their being produced in the pulsar magnetosphere. The model gives a satisfactory fit to the overall nebular spectrum and avoids certain difficulties associated with the conventional model, the most important diffulty being that the difference between the radio and X-ray spectral indices is observed to be 1.0 whereas the conventional model predicts 0.5. Magnetic fields of 2x10$sup -4$ gauss in the outer reaches of the nebula and 3x10$sup -5$ gauss near the pulsar are predicted, where Fermi acceleration is believed to occur, and where hydromagnetic activity is observed. A cutoff in the nebular $gamma$-ray spectrum between 1 and 10 MeV is expected. (AIP)