Angular Distribution Of Emission Research Articles

5105. Relations between the orientations of ion bombarded single crystals, resulting surface structures and sputtered spot patterns: V Alexander et alRad Effects,56 ( [formula omitted]), 1981, 241–250

The sputtering yield of molybdenum and angular distribution of sputtered molybdenum under oxygen exposure have been measured for D+- and He+-irradiation in the energy region from 2.5 keV to 6 keV at temperatures ranging from ambient room temperature to 640°C. The components of the sputtered particles from oxygen-exposed molybdenum have also been measured for 8 keV Ar+-irradiation at temperatures of 25°C and 485°C. The yields were determined from the weight loss of the targets and by the aid of the collector method which was applied to determine the angular emission distribution. Components of the sputtered particles were determined by means of the mass analysis of emitted neutral and charged particles. It was found that the oxygen exposure dependence of the yield strongly depends on the incident ions and on the temperature. The results are interpreted in terms of the chemical reactivity of the incident ions with oxygen, a dilution of metal atoms in the oxygen-exposed surface and a beam-induced desorption of Mo-oxide molecules.

5102. A molecular dynamics simulation study of the influence of the ionatom potential function upon sputtering: Don E Harrison, JrJ Appl Phys,52 (3), 1981, 1499–1508

The sputtering yield of molybdenum and angular distribution of sputtered molybdenum under oxygen exposure have been measured for D+- and He+-irradiation in the energy region from 2.5 keV to 6 keV at temperatures ranging from ambient room temperature to 640°C. The components of the sputtered particles from oxygen-exposed molybdenum have also been measured for 8 keV Ar+-irradiation at temperatures of 25°C and 485°C. The yields were determined from the weight loss of the targets and by the aid of the collector method which was applied to determine the angular emission distribution. Components of the sputtered particles were determined by means of the mass analysis of emitted neutral and charged particles. It was found that the oxygen exposure dependence of the yield strongly depends on the incident ions and on the temperature. The results are interpreted in terms of the chemical reactivity of the incident ions with oxygen, a dilution of metal atoms in the oxygen-exposed surface and a beam-induced desorption of Mo-oxide molecules.

Angular distribution of coherent Raman emission in degenerate four-wave mixing with pumping by a single diffraction coupled laser beam: configurations for high spatial resolution

This paper contains a discussion of the relation between the angular distributions of the coherently emitted radiation and the angular distribution of the incident beams in a degenerate four-wave mixing experiment, when two of the input beams are derived from the same laser source. The objective of the discussion is to obtain beam configurations that permit the use of such spectroscopic techniques when good spatial resolution is required so that the conventional collinear phase matching geometry is inappropriate. Two different configurations are indeed obtained and experimentally demonstrated that have, in the worst direction (longitudinal), spatial resolution of the order of 1 mm, with beam apertures comparable with those used in the standard collinear experiments and without the complicating requirement of two distinct pump beams.

Charged-particle emission in reactions of 15-MeV neutrons withY89,Zr90, andMo92,94,95,96

Charged-particle emission cross sections, spectra, and angular distributions have been measured for targets of /sup 89/Y, /sup 90/Zr, and /sup 92,94,95,96/Mo bombarded with 14.8-MeV neutrons. A magnetic quadrupole spectrometer served to detect the charged particles. Evidence for both statistical and pre-equilibrium reaction mechanisms was found in the proton, deuteron, and alpha-particle emission. The cross sections and spectra are compared with calculations based on these reaction models.

Evidence of suprathermal electron fluxes in laser-produced plasma from the polarization and anisotropy of X-ray bremsstrahlung emission

Polarization and angular distribution of suprathermal X-ray emission from plasma produced by picosecond ruby laser pulses have been measured. Polarization of 12 ± 3 percent and anisotropy of X-ray angular distribution evidence the existence of suprathermal electron fluxes in plasma. Their direction corresponds to resonance absorption mechanism.

X-ray emission from plasma produced by a picosecond ruby laser

The spectrum and angular distribution of the X-ray continuum emission from a picosecond ruby laser produced plasma has been investigated. Massive plane targets made of 20 different elements were used. The dependence of the electron temperature and the effective temperature of suprathermal electrons on the atomic number of the target was determined as well as the dependence of the suprathermal electron temperature on the laser intensity. The most probable mechanism of suprathermal electron generation is resonance absorption.

Angular emission profiles of dye molecules excited by surface plasmon waves at a metal surface

The angular distribution of fluorescence emission from dye molecules excited by surface plasmon waves in a silver film is reported. Coupling of the emitted fluorescence to a surface plasmon mode at the Stokes shifted wavelength results in a sharply peaked angular profile in the prism half space. Fresnel theory is used to model experimental results obtained for thick and thin sample dye films and for micron-size particles containing dye.

Sputter-erosion and impurity emission from titanium and vanadium at low-energy ion bombardment

Titanium and vanadium have been irradiated with inert as well as reactive ions while exposed to varying gas pressures of H 2, N 2 and O 2. The general effect of reactive gas atoms on Ti and V surfaces is a reduction of the sputtering yield, an enhancement of the ionized fraction of ejected particles, and a suppression of surface topographical effects; oxygen was found to be most effective in all respects. The angular emission distribution is only weakly affected and conforms closely to a cosine distribution, with a tendency to an “over-cosine” distribution at very low energies and light ions. p]Further evidence was found for promoted incorporation of gas atoms into the solid when the exposure to the gas phase is accompanied by energetic particle irradiation.

Pinhole imaging of fast ions from laser-produced plasmas

Pinhole-camera images formed by fast ions emitted from spherical-glass-shell targets uniformly irradiated by intense 1.06-μm laser light have been recorded on cellulose-nitrate films. The spatial resolution of the images is consistent with the 5- and 9-μm pinhole size. The size of the image relative to the target size provides the first measurement of the angular distribution of fast-ion emission from spherical targets. The observed images indicate a forward-peaked distribution, but with very broad angular spread. Image sizes increase with laser intensity and pulse length.

Historical Introduction

This program has been organized by the EMSA to commensurate the 50th anniversary of the experimental verification of the wave nature of the electron. Davisson and Germer in the U.S. and Thomson and Reid in Britian accomplished this at about the same time. Their findings were published in Nature in 1927 by mutual agreement since their independent efforts had led to the same conclusion at about the same time. In 1937 Davisson and Thomson shared the Nobel Prize in physics for demonstrating the wave nature of the electron deduced in 1924 by Louis de Broglie.The Davisson experiments (1921-1927) were concerned with the angular distribution of secondary electron emission from nickel surfaces produced by 150 volt primary electrons. The motivation was the effect of secondary emission on the characteristics of vacuum tubes but significant deviations from the results expected for a corpuscular electron led to a diffraction interpretation suggested by Elasser in 1925.

Structure of the Steady State SGEMP Boundary Layer

When X rays illuminate a material surface they eject electrons backwards which then congregate in a relatively thin layer near the surface. We study the structure of this layer in the steady state limit in the cases in which the electron emission angular distribution is proportional to cosθ, where θ is the emission angle measured from normal, and when the electron energy distribution is either exponential or linear times exponential. These cases closely approximate the real world when the incident X-ray source has a blackbody spectrum.

X-ray structure of the Puppis supernova remnant

The angular distribution of X-ray emission from the Puppis supernova remnant was investigated with a focusing X-ray collector during a rocket observation. Extent of the X-ray emitting region along the direction of scan is 42 (+ or - 4) arcmin and is well correlated with the size of the Puppis A radioshell. The existence of a feature within the remnant is confirmed whose X-ray emission is strongly localized, and its spectrum is observed to be softer than the rest of the remnant.

Spectra and angular distributions of electrons emitted from laser-produced plasmas

The spectra and angular distributions of high-energy electrons emitted from laser-produced plasmas have been measured. The plasmas were produced using short pulses from both CO2 and Nd : glass lasers to irradiate polyethylene slabs. For a CO2 laser intensity of approximately 3×1014 W/cm2 we find at least an order of magnitude greater energy conversion to high-energy electrons than with a Nd : glass laser intensity of approximately 5×1015 W/cm2. The angular distribution of electron emission is strongly peaked along the target normal (i.e., density gradient) and fine angular structure is observed.

Field electron cathode stability studies: Zirconium/tungsten thermal-field cathode

The emission angular distribution, total energy distribution, noise spectrum, and emitter life have been measured for the W/Zr thermal-field cathode. The results give an emitter life in excess of 1000 h at T=1350 to 1450 K, P?2×10−8 Torr, and a total current of ∼100 μA. A low-noise highly confined beam long the (100) direction can be obtained. A source brightness of 1010 A/cm2 sr at 3 kV and an energy spread of less than 0.9 eV were measured under operational conditions.

Diffraction effects in low-energy electron emission

The origin of diffraction peaks in the energy distribution of intensity of low-energy (< 1000 eV) electron emission from crystals is discussed from the standpoint of the dynamical theory of diffraction. The emitted electrons are considered to originate at relatively incoherent point sources in the crystal. The two-beam approximation of dynamical theory is used. The theory accounts for the chief regularities of diffraction peaks: temperature-dependence of peak intensities like that for low-energy electron diffraction (LEED) peaks, correlation of peak energies with X-ray absorption fine structure, and correlation of peak energies with the energies of normal-incidence LEED peaks in specular reflection. It is shown that the conditions for diffraction peaks coincide with the conditions for emergence of Kikuchi lines. It is predicted that for energies just above those of diffraction peaks, such emergences should be observable in the angular distribution of emission as intensity minima for emission along low-index crystal axes. Theory of Kikuchi band profiles is developed in an Appendix.

Height Distribution and Directionality of 2-12 a X-Ray Flare Emission in the Solar Atmosphere

view Abstract Citations (26) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Height Distribution and Directionality of 2-12 a X-Ray Flare Emission in the Solar Atmosphere Catalano, Charles P. ; van Allen, James A. Abstract The emission of soft X-rays (2-12 A) in solar flares has been studied in a new way by using simultaneous observations by two spacecraft near the Earth (Explorers 33 and 35) and another at a markedly different heliocentric longitude (Mariner 5) during the 117-day period 1967 July 28- November 21. Detailed intensity versus time observations on 607 separate flares were obtained. The principal findings are as follows: (a) The effective temperature T of the emitting plasma is (8 1 2) x 106 K for flares of small and moderate intensity. T increases to 20 x 106 K for the most intense flares. (b) The angular distribution of emission is independent of solar zenith angle to an accuracy of a few percent. (c) For flares that are fully visible from one spacecraft but partly occulted by the solar disk as viewed by the other, the dependence of soft X-ray emission I on altitude h above the photosphere is found to be well represented by dI/dh cc exp (- hIh0) with h0 = (11 1 3) x 10 km. Subject headings: flares, solar - X-rays, solar Publication: The Astrophysical Journal Pub Date: October 1973 DOI: 10.1086/152420 Bibcode: 1973ApJ...185..335C full text sources ADS |

Asymmetry of Soft X-Ray Emission Near M87

view Abstract Citations (21) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Asymmetry of Soft X-Ray Emission Near M87 Catura, R. C. ; Fisher, P. C. ; Johnson, H. M. ; Meyerott, A. J. Abstract The angular distribution of X-ray emission near M87 has been measured at energies from 0.5 to 4 keV by a rocket-borne X-ray optical system. The observed distribution has an angular extent of 0?4 i 0? I and contains a compact component, coincident with M87, which is small compared with the instrument's angular resolution of 0? 1. The extended source is not centered on M87 but displaced by 0?2 ::::: 0?05 in the approximate direction of the bright jet associated with this galaxy. Publication: The Astrophysical Journal Pub Date: October 1972 DOI: 10.1086/181041 Bibcode: 1972ApJ...177L...1C full text sources ADS | data products NED (1)

The Computation of Photon Radiation Induced Electron Emission

In recent years a variety of models have been developed for the computation of the photon radiation-induced electron emission from matter, ranging from pure Monte Carlo models, which while rigorous are quite costly for application as an engineering tool, to pure analytical models, which while convenient and inexpensive have strictly limited ranges of validity. The limitations of analytical models due to the neglect of Auger and secondary contributions to the emission current and due to the neglect of electron multiple scattering in the emission calculation are examined in this paper. A one-dimensional model is developed for predicting the relative magnitudes of the photoelectron, Compton, Auger, and secondary electron contributions to the emission current, and the model predictions are correlated with experimental data. It is concluded that a generally applicable emission model should include treatment of the Auger and secondary electrons as well as the photoelectrons and Compton electrons. The significance of electron multiple scattering in the calculation of the emission is examined through comparisons of analytical, Monte Carlo, and experimental data. It is concluded that while multiple scattering may be neglected in the calculation of forward emission efficiency, it must not be neglected in the calculation of backward emission effeciency or angular distribution of emission. An alternative emission computational model is introduced which utilizes a synthesis of analytical and Monte Carlo techniques. Comparisons of the model predictions to experimental data for forward and backward emission efficiency, energy spectrum, and angular distribution are included.

Mass Dependence of the Angular Distribution of Charged-Particle Emission from Crystals: Transition to the Classical Limit

In recent years, the emission of charged particles from crystals has received considerable attention, both experimentally and theoretically. The customary interpretation of the emission partterns has been derived from classical mechanics, which predicts patterns very close to those observed for heavy charged particles (protons, $\ensuremath{\alpha}$ particles) but only qualitatively similar to those exhibited by electrons and positrons. In the present paper, it is shown that at least one consequence of the classical model, namely, mass independence of the angular distribution at constant energy, is violated dramatically by the quantum-mechanical calculation of the emission pattern. Specifically, the emission patterns for electrons and positrons are shown to differ from the emission patterns for much-higher-mass particles by factors of up to 4 in half-width and intensity. The condition under which the classical limit is regained is that the lattice spacing be large, not compared with the particle de Broglie wavelength, but compared, rather, with ${\ensuremath{\lambda}}_{p}=\frac{\ensuremath{\hbar}}{2}{(\mathrm{m}\overline{V})}^{\frac{1}{2}}$, where $\overline{V}$ is an average value for the interaction potential inside the unit cell, and $m$ is the particle mass.

Power and Bandwidth of Spontaneous Parametric Emission

Theoretical and experimental results concerned with the spectral and angular distribution of spontaneous parametric emission are reported. Such emission results when light from a pumping laser is incident on a nonlinear crystal, and does not require that the parametric gain exceed the single-pass crystal loss. The emission is somewhat like spontaneous Raman or Brillouin scattering, but differs in two major respects. First, in a lossless crystal, the bandwidth of the emission is controlled by the crystal length and accepted angular aperture as opposed to a loss mechanism in the Raman or Brillouin case. Second, by changing the crystal temperature or orientation, the spontaneous emission may be tuned over several thousand angstroms. The reported experiments employed a 4880 \AA{} laser as a pump and a 1-cm crystal of LiNb${\mathrm{O}}_{3}$ as the non-linear material. The application of parametric spontaneous emission to the measurement of crystal non-linearities is considered, and the advantages of this method over second-harmonic generation are discussed.