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Full-Text Articles in Physics
State-Selective Capture In Collisions Of Protons With Noble Gases, M. Schulz, D. M. Blakenship, S. W. Bross, A. D. Gaus, Timothy J. Gay, W. Htwe, J. T. Park, J. L. Peacher
State-Selective Capture In Collisions Of Protons With Noble Gases, M. Schulz, D. M. Blakenship, S. W. Bross, A. D. Gaus, Timothy J. Gay, W. Htwe, J. T. Park, J. L. Peacher
Timothy J. Gay Publications
We have measured coincidences between neutral H atoms and Lyman-α photons for collisions between 50-keV protons and noble gases as a function of the projectile scattering angle. The coincidences are dominated by capture to the 2p state of the projectile. While the total cross sections depend strongly on the target, the shape of the angular distribution of the differential cross sections was found to depend only weakly on that parameter. The data indicate that electrons are captured predominantly from the outermost shell of the target atom for the collision systems studied here.
Electron Production In Proton Collisions With Atoms And Molecules: Energy Distributions, M. Eugene Rudd, Y.-K. Kim, D. H. Madison, Timothy J. Gay
Electron Production In Proton Collisions With Atoms And Molecules: Energy Distributions, M. Eugene Rudd, Y.-K. Kim, D. H. Madison, Timothy J. Gay
Timothy J. Gay Publications
All known data on the energy distribution of secondary electrons from collisions of protons with atoms and molecules have been reviewed and differential cross sections have been collected. The two experimental methods used to obtain the data are discussed and possible sources of error pointed out. Theoretical treatments are reviewed and several methods of checking the consistency of the data are discussed. Two semiempirical models have been chosen to represent the differential cross sections, and parameters for these models are given which fit the average of the experimental data, subject to known constraints. Recommended values of differential cross sections are …
Mott Electron Polarimetry, Timothy J. Gay, F. B. Dunning
Mott Electron Polarimetry, Timothy J. Gay, F. B. Dunning
Timothy J. Gay Publications
Electron polarimeters based on Mott scattering are extensively used in atomic and molecular, solid state, nuclear, and high-energy physics. This use stems from the increasing realization that much additional information concerning many physical processes can be obtained through spin-dependent measurements. In this review we discuss the basic physics and application of Mott polarimetry. A number of different Mott polarimeter designs are described that illustrate the wide range of operating energies (10 eV-1 MeV) and geometries that can be used in such instruments. The calibration of Mott polarimeters is discussed together with the potential sources of systematic error that can arise …
Angular-Differential Cross Sections For H(2P) Formation In Intermediate-Energy Proton-Helium Collisions, D. G. Seely, S. W. Bross, A. D. Gaus, J. W. Edwards, D. R. Schultz, Timothy J. Gay, J. T. Park, J. L. Peacher
Angular-Differential Cross Sections For H(2P) Formation In Intermediate-Energy Proton-Helium Collisions, D. G. Seely, S. W. Bross, A. D. Gaus, J. W. Edwards, D. R. Schultz, Timothy J. Gay, J. T. Park, J. L. Peacher
Timothy J. Gay Publications
Angular-differential cross sections for charge transfer with simultaneous emission of a photon in collisions of protons with helium atoms have been measured. The incident proton energies were 25, 50, and 100 keV and the center-of-mass scattering angles were between 0 and 2.0 mrad. In the experiment, hydrogen atoms that scattered through an angle θ were detected in coincidence with photons emitted perpendicular to the scattering plane with a wavelength between 1140 and 1400 Å. Differential cross sections for capture into the 2p state of the hydrogen atom were determined from the variation in the coincidence signal with θ. The …
Extrapolation Procedures In Mott Electron Polarimetry, Timothy J. Gay, M. A. Khakoo, J. A. Brand, J. E. Furst, W. V. Meyer, W. M. K. P. Wijayaratna, F. B. Dunning
Extrapolation Procedures In Mott Electron Polarimetry, Timothy J. Gay, M. A. Khakoo, J. A. Brand, J. E. Furst, W. V. Meyer, W. M. K. P. Wijayaratna, F. B. Dunning
Timothy J. Gay Publications
In standard Mott electron polarimetry using thin gold film targets, extrapolation procedures must be used to reduce the experimentally measured asymmetries A to the values they would have for scattering from single atoms. These extrapolations involve the dependence of A on either the gold film thickness t or the maximum detected electron energy loss in the target ΔE. Using a concentric cylindrical-electrode Mott polarimeter, we have studied and compared these two types of extrapolations over the electron energy range 20-100 keV. The potential systematic errors which can result from such procedures are analyzed in detail, particularly with regard to the …
Production Of A High-Density State-Selected Metastable Neon Beam, J. A. Brand, J. E. Furst, Timothy J. Gay, L. D. Shearer
Production Of A High-Density State-Selected Metastable Neon Beam, J. A. Brand, J. E. Furst, Timothy J. Gay, L. D. Shearer
Timothy J. Gay Publications
We have developed a high-density source of metastable neon and have selectively quenched both metastable species using a standing-wave dye laser. The source is compact, stable, and produces an average intensity of 3.6 x 1014 sr -1 s -1 and a density on target of 7.7 x 106 cm-3.
An Attempt To Observe Mott Scattering Optically, J. E. Furst, Timothy J. Gay, W. M. K. P. Wijayaratna, K. Bartschat, H. Geesmann, M. A. Khakoo, D. H. Madison
An Attempt To Observe Mott Scattering Optically, J. E. Furst, Timothy J. Gay, W. M. K. P. Wijayaratna, K. Bartschat, H. Geesmann, M. A. Khakoo, D. H. Madison
Timothy J. Gay Publications
We report an attempt to make an optical observation of Matt scattering, involving the first studies of inelastic collisions between polarized electrons and a heavy noble gas. Polarization fractions of light emitted by the 5p56p[5/7],(3D3) state of Xe following impact excitation in an axial collision geometry were measured as a funclion of the incident electron energy, and compared with distorted-wave Bom calculations. The theoretical and experimental results agree qualitatively in the energy range where cascade contributions to the photon signal are small. We failed to measure non-zero values of the linear polarization fraction η …
Measurement Of Parity Violation In The Elastic Scattering Of Polarized Electrons From 12C, P. A. Souder, R. Holmes, D. - H. Kim, K. S. Kumar, M. E. Schulze, K. Isakovich, G. W. Dodson, K. W. Dow, M. Farkhondeh, S. Kowalski, M. S. Lubell, J. Bellanca, M. Goodman, S. Patch, Richard Wilson, G. D. Cates, S. Dhawan, Timothy J. Gay, V. W. Hughes, A. Magnon, R. Michaels, H. R. Schaefer
Measurement Of Parity Violation In The Elastic Scattering Of Polarized Electrons From 12C, P. A. Souder, R. Holmes, D. - H. Kim, K. S. Kumar, M. E. Schulze, K. Isakovich, G. W. Dodson, K. W. Dow, M. Farkhondeh, S. Kowalski, M. S. Lubell, J. Bellanca, M. Goodman, S. Patch, Richard Wilson, G. D. Cates, S. Dhawan, Timothy J. Gay, V. W. Hughes, A. Magnon, R. Michaels, H. R. Schaefer
Timothy J. Gay Publications
We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from 12C nuclei. Our result is Aexpt=0.60±0.14±0.02 ppm, where the first error is statistical and the second is systematic. With a beam polarization of 0.37, we compute the isoscalar vector hadronic coupling constant γ̃ to be 0.136±0.032±0.009. The standard model predicts γ̃ =0.155 at the tree level, in agreement with our data.
Orientation Of Hydrogen 2P After Tilted-Foil Excitation, C. J. Liu, Timothy J. Gay, K. P. Schuler
Orientation Of Hydrogen 2P After Tilted-Foil Excitation, C. J. Liu, Timothy J. Gay, K. P. Schuler
Timothy J. Gay Publications
The circular polarization of Lyman-α photons resulting from beam-tilted-foil excited H(2p) was measured at energies between 9 and 20 keV with foil tilt angles up to 60°. Various interaction models are used to fit the data, and their physical significance is discussed.
Elastic Angular Differential Cross Sections For Quasi-Oneelectron Collision Systems At Intermediate Energies: (Na+, Li+)+H And (Mg+, Be+)+He, J. L. Peacher, E. Redd, D. G. Seely, Timothy J. Gay, D. M. Blakenship, J. T. Park
Elastic Angular Differential Cross Sections For Quasi-Oneelectron Collision Systems At Intermediate Energies: (Na+, Li+)+H And (Mg+, Be+)+He, J. L. Peacher, E. Redd, D. G. Seely, Timothy J. Gay, D. M. Blakenship, J. T. Park
Timothy J. Gay Publications
Measurements of elastic angular differential cross sections have been carried out for four quasi-one-electron collision systems at intermediate energies. Data are presented for Na++H collisions at laboratory energies of 35.94, 51.75, 63.89, and 143.75 keV, for Li++H collisions at energies of 19.44 and 43.75 keV, for Mg++He collisions at energies of 30, 66.7, and 150 keV, and for Be++He collisions at an energy of 56.25 keV. The highest energy in each case corresponds to a projectile velocity of (1/2 a.u. Born and Eikonal calculations, in which we model the projectile ion as …
Dynamics Of Antimatter-Atom Collisions, R. E. Olson, Timothy J. Gay
Dynamics Of Antimatter-Atom Collisions, R. E. Olson, Timothy J. Gay
Timothy J. Gay Publications
Classical-trajectory Monte Carlo calculations have been used to study ionizing collisions between charged particles (p, p̅ , ℯ+, ℯ-) and He atoms at an incident velocity of 2.83 a.u. While differences in the total single-ionization cross sections for these projectiles are small, our calculations reveal large effects at all angles in the ionized electron spectra, and provide qualitative evidence for a Barkas effect in p and p̅ collisions. Experimental data agree well with our fully classical calculations, including cross sections involving ejected electrons of long wavelength.
Projectile-Charge Dependence Of Ejected-Electron Spectra, V. D. Irby, Timothy J. Gay, J. Wm. Edwards, E. B. Hale, M. L. Mckenzie, R. E. Olson
Projectile-Charge Dependence Of Ejected-Electron Spectra, V. D. Irby, Timothy J. Gay, J. Wm. Edwards, E. B. Hale, M. L. Mckenzie, R. E. Olson
Timothy J. Gay Publications
We have studied H++He and 3He+++He ionizing collisions at intermediate energies (60 to 120 keV/amu) and have observed a significant shift in the velocity position of the maxima in forward-ejected electron spectra when changing projectiles from protons to α particles. In ionizing collisions, a large portion of the ejected electrons are stranded near the transitory equiforce, or saddle point, position between the target ion and receding projectile. The shift in the electron spectra maxima to smaller velocities, due to changing projectiles from protons to α particles, is consistent with the shift in the saddle-point velocity …
Angular-Differential Studies Of Excitation In Quasi-Oneelectron Collisions At "High" Energy, E. Redd, Timothy J. Gay, D. M. Blakenship, J. T. Park, J. L. Peacher, D. G. Seely
Angular-Differential Studies Of Excitation In Quasi-Oneelectron Collisions At "High" Energy, E. Redd, Timothy J. Gay, D. M. Blakenship, J. T. Park, J. L. Peacher, D. G. Seely
Timothy J. Gay Publications
Qualitative differences have been observed between two types of "quasi-one-electron" collision systems. We have studied valence-electron excitation at "high" energy (relative collision velocities up to 0.5 a.u.) in the Mg++He and Na++H collision systems, and find that while Mg++He collisions are dominated by "direct" excitation, the Na++H collisions exhibit significant "molecular" excitation, even at the highest velocities. This behavior can be understood in terms of the molecular structure of the respective collision complexes, and the energy separation between the ground and first excited states of the valence electron.
Saddle-Point Electrons In Ionizing Ion-Atom Collisions, R. E. Olson, Timothy J. Gay, H. G. Berry, V. D. Irby
Saddle-Point Electrons In Ionizing Ion-Atom Collisions, R. E. Olson, Timothy J. Gay, H. G. Berry, V. D. Irby
Timothy J. Gay Publications
We have studied H++He ionizing collisions, and find that electrons stranded between the two postcollision Coulomb centers dominate the ejected-electron spectra for intermediate (~100 keV) projectile energies. The importance of these electrons is clearly established by our classical calculations which are in qualitative agreement, in both shape and magnitude, with experimental spectra taken by us, and with earlier measurements. These ‘‘saddle-point’’ electrons are produced by a classically understandable mechanism, and are unambiguously observed at nonzero scattering angles.
New Insights Into Mott-Scattering Electron Polarimetry, G. D. Fletcher, Timothy J. Gay, M. S. Lubell
New Insights Into Mott-Scattering Electron Polarimetry, G. D. Fletcher, Timothy J. Gay, M. S. Lubell
Timothy J. Gay Publications
In order to understand some of the systematic effects associated with conventional Mottscattering electron polarization measurements, we analyzed asymmetry data obtained with 94-keV polarized electrons scattered at 120° from gold-foil targets ranging in thickness from 27 to 62 μg/cm2. Based upon an examination of the influence of multiple and plural scattering, we conclude that the precision of such Mott measurements is fundamentally limited by an experimental uncertainty of greater than ±2.5% and an absolute uncertainty of approximately ±5%, considerably worse than is customarily assumed. We believe that similar conclusions can be drawn for measurements made with “compact” cylindrical and spherical …
Angular Differential Cross Sections For The Excitation Of 11S Helium To The 21S And 21P States By 25- To 100-Kev-Proton Impact, T. J. Kvale, D. G. Seely, D. M. Blakenship, E. Redd, Timothy J. Gay, M. Kimura, E. Rille, J. L. Peacher, J. T. Park
Angular Differential Cross Sections For The Excitation Of 11S Helium To The 21S And 21P States By 25- To 100-Kev-Proton Impact, T. J. Kvale, D. G. Seely, D. M. Blakenship, E. Redd, Timothy J. Gay, M. Kimura, E. Rille, J. L. Peacher, J. T. Park
Timothy J. Gay Publications
Angular differential cross sections for the proton-impact excitation of ground-state helium (11S) to the 21S and 21P states have been measured for the first time in the energy range 25 to 100 keV with use of the energy-loss technique. The data indicate that, for very small scattering angles, at 25 keV the 21S differential cross section is greater than the 21P differential cross section. For impact energies greater than 50 keV, the 21P differential cross section clearly dominates over the 21S cross section in the very small scattering …
Experimental Study Of Spin-Exchange Effects In Elastic And Ionizing Collisions Of Polarized Electrons With Polarized Hydrogen Atoms, G. D. Fletcher, M. J. Alguard, Timothy J. Gay, V. W. Hughes, P.F. Wainwright, M. S. Lubell, W. Raith
Experimental Study Of Spin-Exchange Effects In Elastic And Ionizing Collisions Of Polarized Electrons With Polarized Hydrogen Atoms, G. D. Fletcher, M. J. Alguard, Timothy J. Gay, V. W. Hughes, P.F. Wainwright, M. S. Lubell, W. Raith
Timothy J. Gay Publications
Using crossed beams of polarized electrons and polarized hydrogen atoms we have investigated the effect of spin exchange on 90° elastic scattering from 4.4 to 30.3 eV and impact ionization from 14.1 to 197.0 eV. Our results suggest that the range of validity of various theoretical approximation methods is more restricted than had been assumed previously.
Measurement Of Spin-Exchange Effects In Electronhydrogen Collisions: Further Studies Of Impact Ionization, Timothy J. Gay, G. D. Fletcher, M. J. Alguard, V. W. Hughes, P. F. Wainwright, M. S. Lubell
Measurement Of Spin-Exchange Effects In Electronhydrogen Collisions: Further Studies Of Impact Ionization, Timothy J. Gay, G. D. Fletcher, M. J. Alguard, V. W. Hughes, P. F. Wainwright, M. S. Lubell
Timothy J. Gay Publications
Using a Fano-effect polarized electron source and a state-selected thermally dissociated hydrogen beam, we measured the interference between the direct and exchange scattering amplitudes for electron-impact ionization of atomic hydrogen between 14.1 and 30.3 eV. We report the data from these measurements and the results of corrections applied to previously published data.
Measurement Of Spin-Exchange Effects In Electron-Hydrogen Collisions: 90° Elastic Scattering From 4 To 30 Ev, G. D. Fletcher, M. J. Alguard, Timothy J. Gay, V. W. Hughes, C. W. Tu, P. F. Wainwright, M. S. Lubell, W. Raith, F. C. Tang
Measurement Of Spin-Exchange Effects In Electron-Hydrogen Collisions: 90° Elastic Scattering From 4 To 30 Ev, G. D. Fletcher, M. J. Alguard, Timothy J. Gay, V. W. Hughes, C. W. Tu, P. F. Wainwright, M. S. Lubell, W. Raith, F. C. Tang
Timothy J. Gay Publications
With use of a Fano-effect polarized electron source and a state-selected thermally dissociated hydrogen beam, the interference between the direct and the exchange scattering amplitudes was measured for 90° elastic scattering of electrons from atomic hydrogen for energies between 4 and 30 eV.
Molecular Effects In Beam-Foil Collision-Induced Alignment Of He I, Timothy J. Gay, H. G. Berry, R. Deserio
Molecular Effects In Beam-Foil Collision-Induced Alignment Of He I, Timothy J. Gay, H. G. Berry, R. Deserio
Timothy J. Gay Publications
We have measured the alignment of beam-foil collision-excited states of He I produced by bombarding carbon foils of various (1.3-110 μg/cm2) areal densities with beams of He+ and HeH+. In addition, we have measured the total light yield of several transitions in He I, He II, and H as a function of foil thickness using beams of HeH+ ions. Experiments were done with He-foil exit energies of 125, 500, 550, and 650 keV. He I alignment decreases in all cases for the thinnest foils when molecular projectiles are used. Total light intensities generally increase …
Energy Dependence Of Alignment In Foil Collision-Excited N=3 States Of He I, Timothy J. Gay, H. G. Berry, R. Deserio, H. P. Garnir, R. M. Schectman, N. Schaffel, R. D. Hight, D.J. Burns
Energy Dependence Of Alignment In Foil Collision-Excited N=3 States Of He I, Timothy J. Gay, H. G. Berry, R. Deserio, H. P. Garnir, R. M. Schectman, N. Schaffel, R. D. Hight, D.J. Burns
Timothy J. Gay Publications
We have measured the beam-foil collision-induced alignment of the 3p 1P, 3p 3P, 3d 1D, and 3d 3D states of He I for He+ beam energies between 30 and 1300 keV. The alignment of all four states is found to vary with beam-current density as well as energy. The number of secondary electrons emitted per incident ion, γ, has also been measured as a function of foil temperature and beam energy between 400 and 1400 keV. The rate of change of both alignment and γ with foil temperature exhibits …
Orientation And Alignment Of The 3P 1P And 4D 1D Levels Of Neutral Helium, R. M. Schectman, R. D. Hight, S. T. Chen, L. J. Curtis, H. G. Berry, Timothy J. Gay, R. Deserio
Orientation And Alignment Of The 3P 1P And 4D 1D Levels Of Neutral Helium, R. M. Schectman, R. D. Hight, S. T. Chen, L. J. Curtis, H. G. Berry, Timothy J. Gay, R. Deserio
Timothy J. Gay Publications
The alignment and orientation produced by the tilted-foil excitation of He was studied for a wide range of foil tilt angles and outgoing-atom velocities. In particular, two quantum states of different orbital angular momentum (3p 1P and 4d 1D) were investigated and the results were compared with a number of previously proposed models.
Temperature Dependence Of Alignment Production In He I By Beam-Foil Excitation, Timothy J. Gay, H. G. Berry
Temperature Dependence Of Alignment Production In He I By Beam-Foil Excitation, Timothy J. Gay, H. G. Berry
Timothy J. Gay Publications
We have measured the dependence upon target-foil temperature of the linear polarization fraction (M / I) of the 2s1S-3p1P, 5016-Å transition in He I for ion energies between 60 and 180 keV. The thin carbon exciter foils were heated externally by Nichrome resistance elements. The measurements of Hight et al. are duplicated; the energy and current dependencies of M / I are the same, assuming correspondence between beam heating and external heating. We also observe that γ, the number of secondary electrons produced per incident ion, decreases with increasing foil …
Alignment Of Helium Excited By Thin Carbon Foils, R. D. Hight, R. M. Schectman, H. G. Berry, G. Gabrielse, Timothy J. Gay
Alignment Of Helium Excited By Thin Carbon Foils, R. D. Hight, R. M. Schectman, H. G. Berry, G. Gabrielse, Timothy J. Gay
Timothy J. Gay Publications
We have measured the linear polarization of the 5016-Å, 2s 1S-3p 1P transition of Hei excited by a thin carbon foil perpendicular to the incident He+ beam at ion energies 50-500 keV. We find that the alignment of the 3p 1P term depends upon the beam current density within the range (2- 150 μA cm-2) measured. Oscillations in the dependence of both M / I (the linear polarization fraction) upon energy and the current density variation of M / I with energy are observed. We discuss possible origins of these …
Alignment Of Helium Excited By Thin Carbon Foils, R. D. Hight, R. M. Schectman, H. G. Berry, G. Gabrielse, Timothy J. Gay
Alignment Of Helium Excited By Thin Carbon Foils, R. D. Hight, R. M. Schectman, H. G. Berry, G. Gabrielse, Timothy J. Gay
Timothy J. Gay Publications
We have measured the linear polarization of the 5016-Å, 2s 1S-3p 1P transition of Hei excited by a thin carbon foil perpendicular to the incident He+ beam at ion energies 50-500 keV. We find that the alignment of the 3p 1P term depends upon the beam current density within the range (2- 150 μA cm-2) measured. Oscillations in the dependence of both M / I (the linear polarization fraction) upon energy and the current density variation of M / I with energy are observed. We discuss possible origins of these variations.