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Full-Text Articles in Physics
Extrapolation Procedures In Mott Electron Polarimetry, Timothy James 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 James Gay, M. A. Khakoo, J. A. Brand, J. E. Furst, W. V. Meyer, W. M.K.P. Wijayaratna, F. B. Dunning
Physics Faculty Research & Creative Works
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 …
Mott Electron Polarimetry, Timothy James Gay, F. B. Dunning
Mott Electron Polarimetry, Timothy James Gay, F. B. Dunning
Physics Faculty Research & Creative Works
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 …
Production Of A High-Density State-Selected Metastable Neon Beam, J. A. Brand, J. E. Furst, Timothy James Gay, Laird D. Schearer
Production Of A High-Density State-Selected Metastable Neon Beam, J. A. Brand, J. E. Furst, Timothy James Gay, Laird D. Schearer
Physics Faculty Research & Creative Works
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 3.6x1014 sr-1 s-1 and a density on target of 7.7x106 cm-3.
Calculation Of The Residual Resistivity And The Thermoelectric Power Of Sp Impurities In Silver, Thomas Vojta, Ingrid Mertig, Rudolf Zeller
Calculation Of The Residual Resistivity And The Thermoelectric Power Of Sp Impurities In Silver, Thomas Vojta, Ingrid Mertig, Rudolf Zeller
Physics Faculty Research & Creative Works
We present ab initio calculations for the residual resistivity and the thermopower of sp impurities in silver. The calculations are based on density-functional theory and the Korringa-Kohn-Rostoker Greens-function method. The linearized Boltzmann equation is solved by means of a Fermi-surface harmonic expansion to calculate the residual resistivity, taking into account the anisotropic electronic properties of the dilute alloy. The thermoelectric power was obtained from the energy dependence of the residual resistivity by means of Mott's formula. The results are in satisfying agreement with highly precise experimental results and confirm experimentally obtained deviations from a quadratic dependence on the valence difference …
Classical Description And Calculation Of Ionization In Collisions Of 100 Ev Electrons And Positrons With He And H2, D. R. Schultz, L. Meng, Ronald E. Olson
Classical Description And Calculation Of Ionization In Collisions Of 100 Ev Electrons And Positrons With He And H2, D. R. Schultz, L. Meng, Ronald E. Olson
Physics Faculty Research & Creative Works
In order to explore the range of applicability of the classical trajectory Monte Carlo technique concerning the phenomena associated with light-particle impact of atoms and molecules we present calculations of the singly and doubly differential cross sections for 100 eV electron and positron impact of He and H2 Through comparison with experimental measurements it is noted in what regimes of ejection energy and angle the classical model describes reasonably the process of ionization by electrons. We find that reasonable agreement is obtained regarding the integrated (singly differential and total) cross sections while the features of the doubly differential cross …
Line Emission From C⁶⁺, O8+ + Li Electron Capture Collisions, Ronald E. Olson, J. Pascale, R. Hoekstra
Line Emission From C⁶⁺, O8+ + Li Electron Capture Collisions, Ronald E. Olson, J. Pascale, R. Hoekstra
Physics Faculty Research & Creative Works
Electron capture cross sections to nl sublevels have been calculated for 1-10keVu−1 collisions of C6+ and O8+ projectiles on a Li target. The classical trajectory Monte Carlo method has been employed with the initial phase distributions for the Li(2s) target obtained from Hartree-Fock calculations. The cross sections are found to maximize at π = 7 for C6+ and n = 8−9 for O8+. The nl cross sections were used to calculate Δ n = 1 line emission cross sections. Comparison of these cross sections with the experimental results of Wolfruni et al indïoitçs good …
State-Selective Capture In Collisions Of Protons With Noble Gases, Michael Schulz, D. M. Blankenship, S. W. Bross, A. D. Gaus, Timothy Gay, W. T. Htwe, John T. Park, Jerry Peacher
State-Selective Capture In Collisions Of Protons With Noble Gases, Michael Schulz, D. M. Blankenship, S. W. Bross, A. D. Gaus, Timothy Gay, W. T. Htwe, John T. Park, Jerry Peacher
Physics Faculty Research & Creative Works
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.
Diffraction In The Binary Encounter Electron Peak Observed In Collisions Of 0.6 Mev Amu⁻¹ I7+, I23+ And Au11+ Projectiles With He And Ar, W. Wolff, J. L. Shinpaugh, H. E. Wolff, Ronald E. Olson, Jee-Ching Wang, S. Lencinas, D. Piscevic, R. Herrmann, H. Schmidt-Böcking
Diffraction In The Binary Encounter Electron Peak Observed In Collisions Of 0.6 Mev Amu⁻¹ I7+, I23+ And Au11+ Projectiles With He And Ar, W. Wolff, J. L. Shinpaugh, H. E. Wolff, Ronald E. Olson, Jee-Ching Wang, S. Lencinas, D. Piscevic, R. Herrmann, H. Schmidt-Böcking
Physics Faculty Research & Creative Works
Relative double differential cross sections for electron emission from collisions of 0.6 MeV amu-1I7+and I23+ projectiles with Ar and Au11+projectiles with He were measured for electron energies from 100 eV to 2000 eV and for angles from 0° to 50°. Experimentally observed sudden shifts of the position of the binary encounter peak were interpreted as resulting from quantum interference in the scattering of target electrons from the partially stripped projectile ion. To this end calculations for the elastic scattering of free electrons initially at rest in the laboratory reference frame from the screened …
Absolute Triple Differential Cross Section For Ionization Of Helium Near Threshold, T. Rösel, Jochen Röder, Leslie S. Frost, Kurt Jung, Hendrik Ehrhardt, Stephenie J. Jones, Don H. Madison
Absolute Triple Differential Cross Section For Ionization Of Helium Near Threshold, T. Rösel, Jochen Röder, Leslie S. Frost, Kurt Jung, Hendrik Ehrhardt, Stephenie J. Jones, Don H. Madison
Physics Faculty Research & Creative Works
Absolute measurements with an accuracy of 22% and theoretical results in a distorted-wave Born approximation (DWBA) are reported for the triple-differential cross section for 26.6-eV electron-impact ionization of helium. An apparatus is used that allows all scattering angles to be independently varied for both coplanar and noncoplanar geometries. The measurements are compared with a DWBA calculation that includes exchange distortion in the calculation of the distorted waves, as well as with earlier calculations by Crothers [J. Phys. B 19, 463 (1986)] and Pan and Starace [Phys. Rev. Lett. 67, 185 (1991)]. Emphasis is placed on understanding the mechanisms for near-threshold …
Adiabatic Cooling Of Atoms By An Intense Standing Wave, Jian Chen, J. Greg Story, Jeffrey J. Tollett, Randall G. Hulet
Adiabatic Cooling Of Atoms By An Intense Standing Wave, Jian Chen, J. Greg Story, Jeffrey J. Tollett, Randall G. Hulet
Physics Faculty Research & Creative Works
Lithium atoms channeled in the nodes of an intense standing-wave radiation field are cooled to near the recoil limit by adibatically reducing the radiation intensity. The final momentum distribution has a narrow component with a root-mean-squared momentum of 2ħk in one dimension, where ħk is the momentum of a radiation-field photon. The data are compared with the results of a Monte Carlo simulation using a two-level atom model. This process may be useful for cooling and increasing the phase-space density of atoms confined in a magnetic trap.
Quasi-Discretization Of The Electron Continuum Emitted In Collisions Of 0.6 Mev U−¹ Au11+ With Noble Gases, S. Hagmann, W. Wolff, J. L. Shinpaugh, H. E. Wolf, Ronald E. Olson, C. P. Bhalla, R. Shingal, C. Kelbch, R. Herrmann, O. Jagutzki, R. Dörner, R. Koch, J. Euler, U. Ramm
Quasi-Discretization Of The Electron Continuum Emitted In Collisions Of 0.6 Mev U−¹ Au11+ With Noble Gases, S. Hagmann, W. Wolff, J. L. Shinpaugh, H. E. Wolf, Ronald E. Olson, C. P. Bhalla, R. Shingal, C. Kelbch, R. Herrmann, O. Jagutzki, R. Dörner, R. Koch, J. Euler, U. Ramm
Physics Faculty Research & Creative Works
We have measured relative doubly differential cross sections for electron emission in collisions of 0.6 MeV u−1 Au11+ projectile ions with He, Ne and Ar targets for laboratory electron-detection angles between 17' and 80' and electron energies from 100 eV to well above the classical binary encounter region. The authors observe that, independent of the target Zt, the electron spectra display three characteristic peak-line structures whose energies are nearly invariant with observation angle. These structures are attributed to the diffraction of quasi-free target electrons in the potential of the projectile. © 1992 IOP Publishing Ltd.
Electron Emission From Foils Induced By Energetic Heavy-Ion Impact, R. A. Sparrow, Ronald E. Olson, D. Schneider
Electron Emission From Foils Induced By Energetic Heavy-Ion Impact, R. A. Sparrow, Ronald E. Olson, D. Schneider
Physics Faculty Research & Creative Works
Doubly differential cross sections have been measured and calculated for the electron emission produced by collisions of 3.5 MeV u−1 U38+ on thin carbon foils. The electron emission is observed in both forward and backward directions. Calculations are in reasonable agreement with the experimental results in both shape and absolute magnitude. At intermediate foil thicknesses, a double binary peak structure is observed that is due to 0° binary electrons being elastically scattered to angle θ along with those that are produced at θ and suffer no large-angle scattering events in the foil. Absolute electron yields show that several …
Electron Production In Proton Collisions With Atoms And Molecules: Energy Distributions, M. Eugene Rudd, Yongki Kim, Don H. Madison, Timothy Gay
Electron Production In Proton Collisions With Atoms And Molecules: Energy Distributions, M. Eugene Rudd, Yongki Kim, Don H. Madison, Timothy Gay
Physics Faculty Research & Creative Works
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 …
Angular-Differential Cross Sections For H(2p) Formation In Intermediate-Energy Proton-Helium Collisions, Denver G. Seely, S. W. Bross, A. D. Gaus, John Wm Edwards, David R. Schultz, Timothy Gay, John T. Park, Jerry Peacher
Angular-Differential Cross Sections For H(2p) Formation In Intermediate-Energy Proton-Helium Collisions, Denver G. Seely, S. W. Bross, A. D. Gaus, John Wm Edwards, David R. Schultz, Timothy Gay, John T. Park, Jerry Peacher
Physics Faculty Research & Creative Works
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 experimental …
Mössbauer And Neutron Diffraction Studies Of Y₂(Fe₁₋ₓmnₓ)₁₄B, Oran Allan Pringle, Gaya Kanishka Marasinghe, Gary J. Long, William Joseph James, William B. Yelon, Decai Xie, Fernande Grandjean
Mössbauer And Neutron Diffraction Studies Of Y₂(Fe₁₋ₓmnₓ)₁₄B, Oran Allan Pringle, Gaya Kanishka Marasinghe, Gary J. Long, William Joseph James, William B. Yelon, Decai Xie, Fernande Grandjean
Physics Faculty Research & Creative Works
We have used Mössbauer spectroscopy and neutron diffraction to study a series of Y2(Fe1-xMnx)1 4B samples in the composition range from x=0.0 to 0.4. Y 2(Fe0.6Mn0.4)14B is paramagnetic at both room temperature and 85 K. The iron quadrupole splitting in this paramagnetic compound allows us to place an upper limit on the quadrupole shift in the magnetic Y2(Fe1-xMnx) 14B alloys. Refinement of Y2(Fe 1-xMnx)14B neutron diffraction data have been used to …
Magnetic Properties Of A Novel Iron Carbide Film, Fe₇C₃X Formed In A Glow Discharge, Oran Allan Pringle, Gary J. Long, Fernande Grandjean, Jun L. Li, George C. Hadjipanayis, William Joseph James
Magnetic Properties Of A Novel Iron Carbide Film, Fe₇C₃X Formed In A Glow Discharge, Oran Allan Pringle, Gary J. Long, Fernande Grandjean, Jun L. Li, George C. Hadjipanayis, William Joseph James
Physics Faculty Research & Creative Works
No abstract provided.
°-Electron Emission In Fast Heavy Ion Atom Collisions, H. Schmidt-Böcking, U. Ramm, G. Kraft, J. Ullrich, H. Berg, C. Kelbch, Ronald E. Olson, R. (Robert) D. Dubois, S. Hagmann, F. Jiazhen
°-Electron Emission In Fast Heavy Ion Atom Collisions, H. Schmidt-Böcking, U. Ramm, G. Kraft, J. Ullrich, H. Berg, C. Kelbch, Ronald E. Olson, R. (Robert) D. Dubois, S. Hagmann, F. Jiazhen
Physics Faculty Research & Creative Works
Biological damages such as mutations, chromosomal aberrations etc. are consequence of biochemical changes mostly in the DNA /1/. With ionizing radiation, these chemical changes are due to primary ionization events and secondary ionization effects caused by the primarily produced electrons. Differences in the biological response of densely ionizing radiation, like heavy charged particles, in comparison to sparsely ionizing radiation, such as X- or γ-rays, are mainly due to the differences in the productions of the so called δ-electrons. Therefore, the emission process of electrons i.e., the cross section for the primary ionization event as well as the energy and angular …
Differential Cross Sections For State-Selective Electron Capture In 25100-Kev Proton-Helium Collisions, D. R. Schultz, C. O. Reinhold, Ronald E. Olson, D. G. Seely
Differential Cross Sections For State-Selective Electron Capture In 25100-Kev Proton-Helium Collisions, D. R. Schultz, C. O. Reinhold, Ronald E. Olson, D. G. Seely
Physics Faculty Research & Creative Works
Cross sections differential in the scattering angle of the projectile are presented for electron capture summed over all states and to the 2s, 2p, 3s, 3p, 4s, and 4p states of hydrogen in 25-, 50-, and 100-keV proton-helium collisions. The classical-trajectory Monte Carlo (CTMC) technique was employed for these calculations as well as to compute total cross sections as a function of impact energy. The latter are compared with experiment to display the behavior of the integral state-selective cross sections in this energy regime. Detailed comparison is also made between the calculated angular differential cross sections and the experimental measurements …
Pressure And Temperature Effects On The Energy Of Formation For Silicon Clusters, Sung-Ho Suck Salk, Chen K. Lutrus, Donald E. Hagen, T. Oshiro, Steven M. Beck, Gary L. Loper
Pressure And Temperature Effects On The Energy Of Formation For Silicon Clusters, Sung-Ho Suck Salk, Chen K. Lutrus, Donald E. Hagen, T. Oshiro, Steven M. Beck, Gary L. Loper
Physics Faculty Research & Creative Works
At present most theoretical studies of atomic clusters are limited to their physical properties referred to 0 K. To the best of our knowledge, there exists no theoretical study of the simultaneous dependence of cluster formation and cluster-size distributions on both pressure and temperature. In the present work both pressure and temperature effects on the formation of silicon clusters are explored. A universal semiempirical formula is obtained to show a general trend in the variation of binding energy as a function of cluster size for both atomic and molecular clusters.
Plasma As A High-Charge-State Projectile Stripping Medium, G. D. Alton, R. A. Sparrow, Ronald E. Olson
Plasma As A High-Charge-State Projectile Stripping Medium, G. D. Alton, R. A. Sparrow, Ronald E. Olson
Physics Faculty Research & Creative Works
The classical trajectory Monte Carlo model has been used to computationally study the charge-state distributions that result from interactions between a high-energy, multielectron projectile and neutral and fully ionized targets. These studies are designed to determine the properties of a plasma for producing highly stripped ions as a possible alternative to gas and foil strippers that are commonly used to enhance the charge states of energetic ion beams. The results of these studies clearly show that a low-atomic-number, highly ionized plasma can yield higher charge states than a neutral target of the same density. The effect is principally attributable to …
Monte Carlo Study Of A Simple Model Bulk-Ice-Ih System: P-T Melting Behavior At Constant Volume, K. Han, Barbara N. Hale
Monte Carlo Study Of A Simple Model Bulk-Ice-Ih System: P-T Melting Behavior At Constant Volume, K. Han, Barbara N. Hale
Physics Faculty Research & Creative Works
An NVT Metropolis Monte Carlo computer simulation is used to examine the P-T behavior of a constant-density model periodic ice-Ih sample near melting. The ice unit cell with density 0.904 g/cm3 consists of 192 rigid water molecules interacting via the revised central-force potentials (RSL2) of Stillinger and Rahman [J. Chem. Phys. 68, 666 (1978)] with a cutoff. Intramolecular parameters are determined from a minimization of the total potential energy of the ice-Ih structure at 0 K. In the P-T plot, emergence of the liquid-solid coexistence region is signaled by a change in sign of dP/dT (when expansion occurs upon …
Dynamic Mechanisms Of He Single Ionization By Fast Proton Impact, A. Gensmantel, J. Ullrich, R. Dörner, Ronald E. Olson, K. Ullmann, E. Forberich, S. Lencinas, H. Schmidt-Böcking
Dynamic Mechanisms Of He Single Ionization By Fast Proton Impact, A. Gensmantel, J. Ullrich, R. Dörner, Ronald E. Olson, K. Ullmann, E. Forberich, S. Lencinas, H. Schmidt-Böcking
Physics Faculty Research & Creative Works
Triple-differential ionization cross sections 3 pdcphipdprec, the momentum distributions of singly charged recoil ions transverse to the beam direction as a function of the projectile polar (p), and azimuthal (cphip) scattering angle were measured in order to elucidate the dynamics of 3-MeV H+ on He single ionization. For projectile polar deflections 0.2 p1 mrad and azimuthal scattering angles 0°cphip360°, the kinematic regimes where two-body interactions dominate the three-body momentum exchange of the single-ionization reaction were separated experimentally. © 1992 The American Physical Society.
Homogeneous Nucleation Of Liquid From The Vapor Phase In An Expansion Cloud Chamber, John L. Schmitt
Homogeneous Nucleation Of Liquid From The Vapor Phase In An Expansion Cloud Chamber, John L. Schmitt
Physics Faculty Research & Creative Works
A Wilson expansion cloud chamber has been used to measure the homogeneous vapor-to-liquid nucleation of several materials over the past decade. These data, representing nucleation rate as a function of temperature and supersaturation ratio for toluene, nonane, and water measured in our center, have been re-examined and are presented both in graphical form and as a table of selected data points. The latter is included for ease of comparison with theory. Measurements of the binary homogeneous nucleation of ethanol-water (E-W) mixtures are also presented. The expansion chamber experimental technique and data reduction technique are discussed.
Classical Calculation Of High-Energy Electron Capture In 5-Mev Proton-Hydrogen Collisions, D. R. Schultz, C. O. Reinhold, Ronald E. Olson
Classical Calculation Of High-Energy Electron Capture In 5-Mev Proton-Hydrogen Collisions, D. R. Schultz, C. O. Reinhold, Ronald E. Olson
Physics Faculty Research & Creative Works
The existence of the classical Thomas peak in the angular distribution of projectiles undergoing capture in collisions of 5-MeV protons with atomic hydrogen is explored using the three-body, three-dimensional classical-trajectory Monte Carlo technique. A method that selects only that portion of the initial phase space which yields capture at this energy was developed to make the calculation tractable due to the extremely small cross section. The spectrum obtained displays only a small shoulder near the angle predicted by Thomas on the basis of successive classical binary collisions and the total (integral) cross section is overestimated by a factor of 26 …