1,469 Matching Results

Search Results

Advanced search parameters have been applied.

Angular distribution of neutrons from a plane surface

Description: From introduction: "This report determines lattice losses by considering the angular distribution of the neutrons emitted from the interior faces of the lattice and the exterior faces of the target. The purpose of this report is to investigate this problem by considering the dimensions of the faces to be large compared to the total mean free path."
Date: 1951
Creator: Harker, Wesley H.
Partner: UNT Libraries Government Documents Department

Photoelectron angular distributions beyond the dipole approximation

Description: This paper reports the measurement of nondipolar asymmetry parameters for the angular distributions of Ar 1s, Kr 2s, and Kr 2p photoemission within 2-3 keV above their respective thresholds. Pronounced asymmetries with respect to direction of photon propagation are present even at low electron kinetic energies. The energy dependence of the asymmetry is Z- and subshell-specific and causes the direction of preferred electron emission to change sign at least once in each case. Towards higher energies, the asymmetry increases and the photoelectron emission pattern is forward-skewed for all 3 cases. Measured asymmetry parameters are in good agreement with recent predictions from nonrelativistic calculations which include interference between electric-dipole and electric-quadrupole transition amplitudes in the photoabsorption process.
Date: August 1996
Creator: Kraessig, B.; Jung, M.; Gemmell, D. S.; Kanter, E. P.; LeBrun, T.; Southworth, S. H. et al.
Partner: UNT Libraries Government Documents Department

Measurement of the angular distribution of electrons from W {right arrow} e{nu} decays observed in p pbar collisions at {squareroot}s = 1.8 TeV

Description: We present a preliminary measurement of the electron angular distribution parameter {alpha}<sub>2</sub> in W {yields} e{nu} events using data collected by the D0 detector during the 1994-1995 Tevatron run. We compare our results with next-to- leading order perturbative QCD, which predicts an angular distribution of (1±{alpha}<sub>1</sub> cos{theta}* +{alpha}<sub>2</sub> cos²{theta}*), where {theta}* is the angle between the charged lepton and the antiproton in the Collins-Soper frame. In the presence of QCD corrections, the parameters {alpha}<sub>1</sub> and {alpha}<sub>2</sub> become functions of p<sup>W</sup><sub>T</sub> , the W boson transverse momentum. We present the first measurement of {alpha}<sub>2</sub> as a function of p<sup>W</sup><sub>T</sub>. This measurement is of importance, because it provides a test of next-to-leading order QCD corrections which are a non-negligible contribution to the W mass measurement.
Date: July 26, 1999
Creator: Abbott, B.
Partner: UNT Libraries Government Documents Department

Initial Measurements on the Angular Distribution of Deuterium Plasma Produced by a Pulsed Spark Source

Description: Abstract: "The deuterium plasma which is ejected by a 6000-ampere pulsed current through a rail-type spark source has a yield in the forward direction which is a factor of 5 to 10 greater than that in the perpendicular direction. This effect is believed to be due to the magnetic propulsion of the plasma."
Date: March 24, 1955
Creator: Bostick, W. H.
Partner: UNT Libraries Government Documents Department

Fragmentation pathwaysfor selected electronic states of theacetylene dication

Description: Coincident measurement of the Auger electron and fragmention momenta emitted after carbon core-level photoionization of acetylenehas yielded new understanding of how the dication fragments. Ab initiocalculations and experimental data, including body-frame Auger angulardistributions, are used to identify the parent electronic states andtogether yield a comprehensive map of the dissociation pathways whichinclude surface crossings and barriers to direct dissociation. The Augerangular distributions show evidence of core-holelocalization.
Date: December 18, 2007
Creator: Osipov, Timur; Rescigno, Thomas N.; Weber, Thorsten; Miyabe,Shungo; Jahnke, T.; Alnaser, A. et al.
Partner: UNT Libraries Government Documents Department

Classical two-slit interference effects in double photoionization of molecular hydrogen at high energies

Description: Recent experiments on double photoionization of H$_2$ with photon energies between 160 and 240 eV have revealed body-frame angular distributions that suggest classical two-slit interference effects may be present when one electron carries most of the available energy and the second electron is not observed. We report precise quantum mechanical calculations that reproduce the experimental findings. They reveal that the interpretation in terms of classical diffraction is only appropriate atsubstantially higher photon energies. At the energies considered in the experiment we offer an alternative explanation based on the mixing of two non-diffractive contributions by circularly polarized light.
Date: July 6, 2008
Creator: Horner, Daniel A.; Miyabe, Shungo; Rescigno, Thomas N; McCurdy, C. William; Morales, Felipe & Martin, Fernando
Partner: UNT Libraries Government Documents Department

The sputter generation of negative ion beams

Description: A brief review is given of recent progress toward a quantitative understanding of negative ion formation by sputtering from surfaces covered with fractional layers of highly electropositive adsorbates. Practical models developed for estimating changes in work functions {Delta}{phi} by electropositive adsorbates are described. The secondary negative ion generation process is examined through the use of composite energy/velocity dependent analytical models. These models are used to illustrate the effect of work function on the energy distributions of negative ions sputter ejected from a polycrystalline molybdenum surface covered with fractional layers of cesium. Predictions are also made of the functional dependence of the probability for negative ion formation on cesium coverage. The models predict energy distributions which are in basic disagreement with experimental observations, implying their inappropriateness for describing the sputter negative ion generation process. We have also developed a model for calculating sputter ratios based on the use of simple scaling procedures to bring Sigmund theory into close agreement with experimental observation accounting for the threshold effect. Scaling factors for projectile energies E > 1000 eV are found to be independent of energy while those for projectile energies E{sub th} < E < 1000 eV were found to be energy dependent. In this study, the model and scaling techniques utilized to bring Sigmund theory into agreement with experiment are discussed in detail and several examples provided which illustrate the versatility, accuracy and utility of the model. In the present report, we describe the model and apply it to the case of sputtering a selected number of metals with energetic cesium ions. In particular, we present sputter ratio information for a number of Cs-projectile/metal-target combinations; the targets are bombarded at normal incidence to the surface.
Date: December 31, 1996
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Energy and angular distributions of radiation power from bending magnet and wiggler sources at a 6-GeV ring

Description: In order to design radiation ports and beam line components, it is essential to understand the distribution of power from a radiation source as a function of both the photon energy and the solid angle of emission. In this preliminary note, we assemble all the formula involved for the case of a bending magnet and a wiggler. Typical distributions are presented for the case of 6-Gev radiation.
Date: September 25, 1985
Creator: Shenoy, G.K. & Viccaro, P.J.
Partner: UNT Libraries Government Documents Department

Nondipolar photoelectron angular distributions

Description: The deviations of photoelectron angular distributions from the simple, highly symmetric shapes predicted within the electric-dipole approximation are investigated. The admixture of an electric-quadrupole component in the photon-atom interaction causes an asymmetry in the angular distribution with respect to the direction of photon propagation. The reported measurement of the angular distributions of argon {ital 1s}, krypton {ital 2s}, and krypton {ital 2p} photoemission within 2-3 keV above their respective thresholds reveal pronounced asymmetries which are present even at low electron kinetic energies. The measured asymmetry parameters are in good agreement with recent predictions from nonrelativistic calculations.
Date: December 31, 1996
Creator: Kraessig, B.; Jung, M.; Gemmell, D.S.; Kanter, E.P.; LeBrun, T.; Southworth, S.H. et al.
Partner: UNT Libraries Government Documents Department

Photon beam polarization and non-dipolar angular distributions

Description: Angular distributions of ejecta from unoriented atoms and molecules depend upon the polarization state of the incident x-rays as well as upon the dynamics of the physical systems being studied. I recommend a simple geometrical way of looking at the polarization and its effects upon angular distributions. The polarization is represented as a vector in a parameter space that faithfully represents the polarization of the beam. The simple dependence of the angular dependence of the angular distributions on the polarization vector enables easy extraction of the dynamical information contained in those angular distributions. No new physical results emerge from this geometrical approach, but known consequences of the symmetries appear in an easily visualized form that I find pleasing and that has proved to be useful for planning experiments and for analyzing data.
Date: August 1, 1996
Creator: Peshkin, M
Partner: UNT Libraries Government Documents Department

Far-field radiation from a cleaved cylindrical dielectric waveguide

Description: Angular spread in the far-field radiation pattern of a cleaved dielectric waveguide is determined from the modal structure at the surface of the waveguide using the Smythe vector integral formulation. Essential features: First, a mode exists in the fiber that has no wavelength cutoff--the so-called HE{sub 11} mode. This mode arises when non-azimuthal angular dependence of the incoming radiation is present. Second, the energy flow from this hybrid mode fills the fiber face and is not annularly shaped as opposed to the symmetric TE and TM modes. Third, the HE{sub 11} mode is not polarization dependent in contrast to the TE and TM modes. Fourth, for small differences in the refractive indices between the core and cladding regions, only the HE{sub 11} mode will be supported until the next modes appear around 3.33{lambda}. At this point, three new modes can propagate and the model structure of the radiation becomes more complicated. Fifth, the far-field radiation pattern will have negligibly small angular dependence in the phases of the vector fields when only the lowest mode is present; the amplitude has an overall angular dependent form factor. Furthermore, when other modes are present (above 3.33{lambda}), the phase of the vector fields will acquire an angular dependence.
Date: July 9, 1996
Creator: Cerjan, C.
Partner: UNT Libraries Government Documents Department

Electron dynamics in the strong field limit of photoionization

Description: High precision photoelectron energy and angular distributions in helium and neon atoms for a broad intensity range reflect the change in the continuum dynamics that occurs as the ionization process evolves into the pure tunneling regime. Elastic rescattering of the laser-driven free electron from its parent ion core leaves a distinct signature on the spectra, providing a direct quantitative test of the various theories of strong field multiphoton ionization. We show that it takes a relatively complete semi-classical rescattering model to accurately reproduce the observed photoelectron distributions. However, the calculated inelastic rescattering rate fails to reproduce the measured nonsequential double ionization yields.
Date: December 31, 1998
Creator: Sheehy, B.; Walker, B.; Lafon, R. & Widmer, M.
Partner: UNT Libraries Government Documents Department

Resonant multiphoton ionization spectra of molecules and molecular fragments. Technical progress report

Description: objectives of this research are the development and application of theoretical techniques for studying several resonant multiphoton ionization processes in molecules. Specific problems of interest pertain to experimental studies of such spectra in which the photoelectron energy and angular distributions are determined.
Date: July 1, 1997
Partner: UNT Libraries Government Documents Department

Next-to-leading order corrections to e{sup +}e{sup -} {yields} four jets

Description: I present a general purpose Monte Carlo program for calculating the next-to-leading order corrections to arbitrary four-jet quantities in electron-positron annihilation. In the current version of the program, some subleading in color terms are neglected. As an example, I calculate the four-jet rate in the Durham scheme as well as the Bengtsson-Zerwas angular distribution at O ({alpha}{sub s}{sup 3}) and compare the results to existing data.
Date: July 1, 1997
Creator: Signer, A.
Partner: UNT Libraries Government Documents Department

Effect of permanent-magnet irregularities in levitation force measurements.

Description: In the measurement of the levitation force between a vertically magnetized permanent magnet (PM) and a bulk high-temperature superconductor (HTS), PM domains with horizontal components of magnetization are shown to produce a nonnegligible contribution to the levitation force in most systems. Such domains are typically found in all PMs, even in those that exhibit zero net horizontal magnetic moment. Extension of this analysis leads to an HTS analog of Earnshaw's theorem, in which at the field-cooling position the vertical stiffness is equal to the sum of the horizontal stiffnesses, independent of angular distribution of magnetic moments within the PM.
Date: October 14, 1999
Creator: Hull, J. R.
Partner: UNT Libraries Government Documents Department

Performance of smoothing by spectral dispersion (SSD) with frequency conversion on the Beamlet Laser for the National Ignition Facility

Description: Simulations and ongoing measurements indicate that SSD results in small degradation to the near field beam quality. The measured effect of SSD bandwidth on conversion to the third harmonic and smoothing of the target illumination will also be described.
Date: November 4, 1997
Creator: Rothenberg, J.E.; Morgan, B.; Wegner, P. & Weiland, T.W.
Partner: UNT Libraries Government Documents Department

RIBE Flux vs. Position Monitor

Description: Recent work at SNL has demonstrated unique capabilities to experimentally measure a variety of ion and neutral particle parameters inside surface features being etched, including ion energy, angular distributions, ion and neutral species measurements. This report details the construction of one recent laboratory tool designed to measure ion beam uniformity over the wafer surface in a reactive ion beam etch system, (RIBE). This information is critical to the development of accurate plasma processing computer models and simulation methods, and is essential for reducing the cost of introducing new processing technologies.
Date: October 1, 2000
Creator: HAMILTON,THOMAS W.
Partner: UNT Libraries Government Documents Department

Sputtering of Bi and Preferential Sputtering of an Inhomogeneous Alloy

Description: Angular distributions and total yields of atoms sputtered from bismuth targets by normally incident 10 keV -50 keV Ne+ and Ar+ ions have been measured both experimentally and by computer simulation. Polycrystalline Bi targets were used for experimental measurements. The sputtered atoms were collected on high purity aluminum foils under ultra-high vacuum conditions, and were subsequently analyzed using Rutherford backscattering spectroscopy. The Monte-Carlo based SRIM code was employed to simulate angular distributions of sputtered Bi atoms and total sputtering yields of Bi to compare with experiment. The measured sputtering yields were found to increase with increasing projectile energy for normally incident 10 keV - 50 keV Ne+ and Ar+ ions. The shapes of the angular distributions of sputtered Bi atoms demonstrated good agreement between experiment and simulation in the present study. The measured and simulated angular distributions of sputtered Bi exhibited an over-cosine tendency. The measured value of the degree of this over-cosine nature was observed to increase with increasing incident Ne+ ion energy, but was not strongly dependent on incident Ar+ ion energy. The differential angular sputtering yield and partial sputtering yields due to Ar ion bombardment of an inhomogeneous liquid Bi:Ga alloy have been investigated, both experimentally and by computer simulation. Normally incident 25 keV and 50 keV beams of Ar+ were used to sputter a target of 99.8 at% Ga and 0.2 at% Bi held at 40° C in ultra-high vacuum (UHV), under which conditions the alloy is known to exhibit extreme Gibbsian surface segregation that produces essentially a monolayer of Bi atop the bulk liquid. Angular distributions of sputtered neutrals and partial sputtering yields obtained from the conversion of areal densities of Bi and Ga atoms on collector foils were determined. The Monte-Carlo based SRIM code was employed to simulate the experiment and obtain the angular ...
Date: December 2014
Creator: Deoli, Naresh T.
Partner: UNT Libraries

Excited charmed mesons

Description: The experimental status of excited charmed mesons is reviewed and is compared to theoretical expectations. Six states have been observed and their properties are consistent with those predicted for excited charmed states with orbital angular momentum equal to one.
Date: May 1, 1995
Creator: Butler, J.N. & Shukla, S.
Partner: UNT Libraries Government Documents Department

Production of jets at the Tevatron

Description: Measurements of the inclusive jet cross section and the dijet angular distribution using data from the Tevatron are presented Comparisons to NLO QCD show good agreement below 250 GeV, but CDF data show an excess at higher E{sub T}; qualitative agreement is seen between the CDF and D0 cross sections. Analysis of the dijet angular distributions exclude quark compositeness below 2.1 TeV.
Date: July 1, 1997
Creator: Heuring, T.
Partner: UNT Libraries Government Documents Department