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Articles 1 - 25 of 25
Full-Text Articles in Physics
Investigation Of The Appropriateness Of Sensitized Luminescence To Determine Exciton Motion Parameters In Pure Molecular Crystals, Vasudev M. Kenkre, Paul Ernest Parris, Dankward B. Schmid
Investigation Of The Appropriateness Of Sensitized Luminescence To Determine Exciton Motion Parameters In Pure Molecular Crystals, Vasudev M. Kenkre, Paul Ernest Parris, Dankward B. Schmid
Physics Faculty Research & Creative Works
A wealth of experimental data has been collected over the years regarding the sensitized luminescence of molecular crystals. Indeed, such observations have played a primary role in attempts to characterize the dynamical aspects of exciton transport in these materials. Nonetheless, as has been noted previously, serious questions of interpretation remain concerning the relationship between primary experimental observables and microscopic parameters which govern exciton transport and capture. In the past these questions have led to an uncertainty, not always acknowledged, in the values of exciton diffusion constants reported in the literature. On the other hand, careful analysis of some recent experiments …
Electron Production In Proton Collisions: Total Cross Sections, M. Eugene Rudd, Yongki Kim, Don H. Madison, Jean W. Gallagher
Electron Production In Proton Collisions: Total Cross Sections, M. Eugene Rudd, Yongki Kim, Don H. Madison, Jean W. Gallagher
Physics Faculty Research & Creative Works
Existing data on the ionization of neutral atoms and molecules by proton impact are reviewed, and electron production cross-section data are collected. The three major experimental methods are discussed and possible sources of error identified. Some theoretical cross sections are discussed, and well-established methods of relating them to measured cross sections are reviewed. A mathematical equation is fitted to the weighted experimental data for each target, and these fits are adjusted to be consistent with appropriate theoretical calculations and with electron impact and photoionization data. Recommended values of total cross sections for proton-impact ionization are given.
Angular Differential Cross Sections For The Excitation Of 1¹S Helium To The 2¹S And 2¹P States By 25- To 100-Kev-Proton Impact, Thomas J. Kvale, Denver G. Seely, D. M. Blankenship, E. Redd, Timothy Gay, Mineo Kimura, Eduard P. Rille, Jerry Peacher, John 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, Thomas J. Kvale, Denver G. Seely, D. M. Blankenship, E. Redd, Timothy Gay, Mineo Kimura, Eduard P. Rille, Jerry Peacher, John T. Park
Physics Faculty Research & Creative Works
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 …
Time-Dependent Magnetic Structures Of The Superconducting Mixed Ternary System Ho(Rh₁₋ₓirₓ)₄B₄, Steven E. Lambert, M. Brian Maple, Oran Allan Pringle, Herbert A. Mook
Time-Dependent Magnetic Structures Of The Superconducting Mixed Ternary System Ho(Rh₁₋ₓirₓ)₄B₄, Steven E. Lambert, M. Brian Maple, Oran Allan Pringle, Herbert A. Mook
Physics Faculty Research & Creative Works
Magnetic structures have been determined by netron diffraction for several compositions in the superconducting mixed ternary system Ho(Rh1-xIrx)4B4. Two features previously reported to occur in the heat capacity for some compositions are shown to correspond to successive magnetic transitions. For x=0.30 and 0.45, neutron diffraction peaks for the lowest temperature structure develop over a timescale of many hours. The results are discussed in terms of magnetic frustration.
Low Temperature Tunneling Dynamics In Condensed Media, Paul Ernest Parris, Robert J. Silbey
Low Temperature Tunneling Dynamics In Condensed Media, Paul Ernest Parris, Robert J. Silbey
Physics Faculty Research & Creative Works
There has been considerable interest recently in the low temperature dynamics of condensed phase tunneling phenomena. In this paper we consider the interplay between quasiparticle transport and vibrational relaxation; the former taking place via tunneling in a double well potential, and the latter occurring due to interactions of the tunneling system with a harmonic bath. Taking the system-bath interactions to be linear in the bath coordinates, and explicitly allowing for a vibrationally excited well, we present a unified treatment of the weak and strong coupling regimes and obtain reduced equations of motion for the tunneling particle position operator. Solutions are …
Small-Angle Neutron Scattering Of (Er₀.₈Ho₀.₂)Rh₄B₄, Oran Allan Pringle, Herbert A. Mook, M. Brian Maple
Small-Angle Neutron Scattering Of (Er₀.₈Ho₀.₂)Rh₄B₄, Oran Allan Pringle, Herbert A. Mook, M. Brian Maple
Physics Faculty Research & Creative Works
The (Er1-xHox)Rh4B4 pseudoternary alloy system has a minimum in the phase boundary between the superconducting and ferromagnetic phases near x=0.3. This minimum has been identified as due to the competing magnetic anisotropies of Er and Ho. It has also been suggested that there could be a Lifschitz point near the minimum. Using the 30-m SANS camera at the National Center for Small-Angle Scattering Research at ORNL, we have observed a peak in the SANS pattern for (Er 0.8Ho0.2)Rh4B4 at Q=0.065 Å-1. This peak appears for …
Spin-Exchange Cross Sections For Hydrogen-Atomalkali-Metal-Atom Collisions, H. R. Cole, Ronald E. Olson
Spin-Exchange Cross Sections For Hydrogen-Atomalkali-Metal-Atom Collisions, H. R. Cole, Ronald E. Olson
Physics Faculty Research & Creative Works
The pseudopotential molecular-structure method has been used to calculate the X1 and a3 interaction potentials for the alkali-metal-atom hydrogen-atom systems. These potentials were then used in a quantum-mechanical calculation to determine the spin-exchange cross sections in the energy range from 2.5x10-4 eV to 2.5 eV. The cross sections follow the general form Q1/2=a-b lnv. However, abundant structure on the cross sections is present due to orbiting resonances induced by the deeply bound well of the X1 molecular state. The spin-exchange cross sections range from 17x10-16 to 25x10-16 cm2 at room temperature for H(F=1) transferring to H(F=0) in collision with unpolarized …
Neutron-Diffraction Study Of The Magnetic Ordering In Ni(Ch₂Co₂Nh₂)₂ 2h₂O, Akifumi Onodera, Yorihiko Tsunoda, Nobuhiko Kunitomi, Oran Allan Pringle, Robert M. Nicklow, Ralph M. Moon
Neutron-Diffraction Study Of The Magnetic Ordering In Ni(Ch₂Co₂Nh₂)₂ 2h₂O, Akifumi Onodera, Yorihiko Tsunoda, Nobuhiko Kunitomi, Oran Allan Pringle, Robert M. Nicklow, Ralph M. Moon
Physics Faculty Research & Creative Works
The magnetic structure of Ni(CH2CO2NH2)2 2 H2O has been determined by the analysis of neutron-diffraction data from powder and single-crystal samples. Ni(CH2CO2NH2)2 2 H2O orders at a Néel temperature of 0.88 K. The magnetic structure consists of antiferromagnetically coupled layers having a canted ferromagnetic ordering within layers, with a moment of (2.33 ± 0.14)μB per Ni2+ ion. The magnetic unit cell is composed of two crystallographic unit cells, and contains four nickel atoms. The moment direction is not simply related …
Erratum: Normalized Line Shapes For Far-Wing Continuum Spectra: The Rb-Xe Satellite Band (Physical Review A(1985) 32, 5 (3150-3152)), Ronald James Bieniek
Erratum: Normalized Line Shapes For Far-Wing Continuum Spectra: The Rb-Xe Satellite Band (Physical Review A(1985) 32, 5 (3150-3152)), Ronald James Bieniek
Physics Faculty Research & Creative Works
Recent advances in experimental spectroscopy offer the promise of yielding much detailed information about molecular potentials and collisional interactions from a study of the light emitted or absorbed in the far wings of atomic lines. However, readily manipulable, accurate theoretical expressions and methods are needed to extract such knowledge. Straightforward formulas, based on the distorted-wave approximation, for the normalized emission intensity in the far wing of a pumped atomic line are given here. By normalizing theoretical spectra with respect to the strength of the atomic line, one obtains a convenient form for the analysis of experimental differential spectra that are …
Electron Capture In Pseudo-Two-Electron Systems: Ar8++He, M. Kimura, Ronald E. Olson
Electron Capture In Pseudo-Two-Electron Systems: Ar8++He, M. Kimura, Ronald E. Olson
Physics Faculty Research & Creative Works
Molecular-structure calculations using the pseudopotential method have been performed on the (ArHe)8+ system. The cross section for single-electron capture in Ar8++He collisions was calculated for energies from 20 eV to 10 keV/amu. The perturbed-stationary-state method [M. Kimura, H. Sato, and R. E. Olson, Phys. Rev. A 28, 2085 (1983)], modified to include electron translation factors appropriate to two-electron systems, was used. The total cross section is relatively energy independent with a value of approximately 2.5x10-15 cm2. The n=4 level of Ar7+ is found to be preferentially populated, with the 4f level being dominant. © 1985 The …
Interaction Of Electric And Magnetic Charges: Addendum, I. Adawi
Interaction Of Electric And Magnetic Charges: Addendum, I. Adawi
Physics Faculty Research & Creative Works
The problem of a head-on collision between a spherically symmetric electric and magnetic charge is reconsidered. The assumption of the equality of the electric and magnetic forces made earlier is abandoned as it does not follow from the model. It is shown that the rotational angular momentum a charge acquires is determined by the amount of the angular momentum which the charge removes from the field by virtue of its extension. The interaction energy of each charge with the dipole it induces in the other charge is equal to the rotational energy of the charge itself. This results in simple …
Electron Capture By Slow Alq+ Ions Colliding With Hydrogen, R. A. Phaneuf, M. Kimura, H. Sato, Ronald E. Olson
Electron Capture By Slow Alq+ Ions Colliding With Hydrogen, R. A. Phaneuf, M. Kimura, H. Sato, Ronald E. Olson
Physics Faculty Research & Creative Works
Total electron-capture cross sections have been measured for collisions of Alq+ (q=210) with H and H2 in the 20120-eV/amu energy range. The general trend of the cross sections for both H and H2 is an approximately linear increase with ionic charge state. The Al2++H and Al3++H systems were investigated theoretically using the molecular-orbital method with a pseudopotential to represent the Al3+ ion core. Coupled-channel calculations realize good agreement with experiment. An anomalously small cross section for Al2++H is attributed to the fact that of the 1 and 3 entrance channels, only the 1 …
Raman Studies Of Heavily Implanted, Dye-Laser-Annealed Gaas, H. D. Yao, A. Compaan, Edward Boyd Hale
Raman Studies Of Heavily Implanted, Dye-Laser-Annealed Gaas, H. D. Yao, A. Compaan, Edward Boyd Hale
Physics Faculty Research & Creative Works
Raman scattering is used to study the annealing behavior produced by 10 nsec, 565 nm dye laser pulses in high dose ion-implanted GaAs. Samples were prepared with Sn and Cd implantations of 2, 5, and 10 x 1015 cm2. The Raman spectra indicate that the threshold for epitaxial growth lies between 0.2 - 0.3 J cm2. Best carrier activation (∼ 2%), however, is achieved at ∼1.6 J cm2 for the Sn-implanted sample (n-type). For Cd implantation the electrical activation appears to be very high ({greater-than or approximate} 50%) for low pulse energies({less-than or approximate} 0.3 J cm2) but decreases for …
Summary Abstract: Computerized Scanning Auger Microprobe, T. J. Sommerer, Edward Boyd Hale
Summary Abstract: Computerized Scanning Auger Microprobe, T. J. Sommerer, Edward Boyd Hale
Physics Faculty Research & Creative Works
No abstract provided.
Computerized Scanning Auger Microprobe, T. J. Sommerer, Edward Boyd Hale
Computerized Scanning Auger Microprobe, T. J. Sommerer, Edward Boyd Hale
Physics Faculty Research & Creative Works
An Auger spectrometer has been automated using a microcomputer. Fundamental considerations in the design and choice of the computerized system are presented and should be of general interest. The spectrometer was a Physical Electronics Ind. model 545 scanning Auger microprobe. The microcomputer chosen was a Southwest Technical Products 6809 computer system. Hardware details are discussed with emphasis on the four computer-spectrometer interface boards. These boards are (1) Auger energy control board, which sets the Auger detection energy with its 16 bit digital-to-analog converter (DAC); (2) read Auger signal board, which reads the Auger signal intensity with its 12 bit analog-to-digital …
Spin-1 Exchange-Interaction Model Of Ferromagnetism, Harry A. Brown
Spin-1 Exchange-Interaction Model Of Ferromagnetism, Harry A. Brown
Physics Faculty Research & Creative Works
The spin-exchange operator for spin S=1 and a constant-coupling-like approximation are used to evaluate the thermodynamic properties of a system described by a two-spin Hamiltonian that includes dipole and quadrupole interactions. The dipole and quadrupole moments and the exchange energy are found as functions of temperature. There is a critical temperature, Tc, which depends on the coordination number of the lattice at which the system undergoes a second-order phase transition. Below Tc, both magnetic moments, simultaneously, take on nonzero values and have infinite derivatives there while the derivative of the exchange energy is discontinuous. Comparison is made with other results …
Laser-Assisted Charge-Transfer Collisions: K++Na, Y. P. Hsu, M. Kimura, Ronald E. Olson
Laser-Assisted Charge-Transfer Collisions: K++Na, Y. P. Hsu, M. Kimura, Ronald E. Olson
Physics Faculty Research & Creative Works
A theory has been formulated to characterize charge-transfer collisions in the presence of an external laser field. The molecular-state-expansion method is used to describe the scattering process within the impact-parameter formalism. Electron translation factors are included in the molecular-state expansion so that the scattering wave function satisfies the correct boundary conditions. The theory is applied to the process K++NaK+Na+. In addition, we have made a detailed analysis of laser-assisted charge transfer for low-energy collisions. In this case, a Landau-Zener formula can be derived which shows that the cross section increases with decreasing incident energy. In general the laser coupling is …
Faraday's Law Demonstration, Richard Sankovich
Faraday's Law Demonstration, Richard Sankovich
Physics Faculty Research & Creative Works
No abstract provided.
Relative Fluorescence Efficiencies For The Dissociative Excitation Of Some Hg-Halides By N2(A ³Σu+), Laird D. Schearer
Relative Fluorescence Efficiencies For The Dissociative Excitation Of Some Hg-Halides By N2(A ³Σu+), Laird D. Schearer
Physics Faculty Research & Creative Works
No abstract provided.
Effects Of Iron Implantation On The Aqueous Corrosion Of Magnesium, S. Akavipat, Edward Boyd Hale, C. E. Habermann, P. L. Hagans
Effects Of Iron Implantation On The Aqueous Corrosion Of Magnesium, S. Akavipat, Edward Boyd Hale, C. E. Habermann, P. L. Hagans
Physics Faculty Research & Creative Works
The influence of the implantation of iron ions on the corrosion of magnesium and an AlZn-rich magnesium alloy (AZ91C) has been studied. Anodic polarization measurements in a dilute chloride-containing alkaline solution were used to evaluate corrosion resistance. A range of ion energies (50-180 keV) and doses (1016-2 x 1017 Fe+ ions cm-2) have been evaluated. Both the iron-implanted pure magnesium and the alloy AZ91C gave improved polarization measurements. A systematic positive shift of the open-circuit potential with increasing iron dose was found. In AZ91C at a dose of 1017 Fe+ ions cm-2, there was a + 0.6 V more noble …
Charge Transfer Of Hydrogen Ions And Atoms In Metal Vapors, T. J. Morgan, Ronald E. Olson, A. S. Schlachter, J. W. Gallagher
Charge Transfer Of Hydrogen Ions And Atoms In Metal Vapors, T. J. Morgan, Ronald E. Olson, A. S. Schlachter, J. W. Gallagher
Physics Faculty Research & Creative Works
Cross sections and equilibrium fractions for energetic H+, H−, and H0 in collisions with metal vapor targets have been compiled and evaluated. Both experimental and theoretical results are reported. Sources of errors are discussed, and recommended values for the data are presented. © 1985, American Institute of Physics for the National Institute of Standards and Technology. All rights reserved.
Evidence For Uncorrelated Electron Capture And K-Shell Excitation In S13++He Collisions, J. A. Tanis, E. M. Bernstein, M. W. Clark, W. G. Graham, Robert H. Mcfarland, T. J. Morgan, B. M. Johnson, K. W. Jones, M. Meron
Evidence For Uncorrelated Electron Capture And K-Shell Excitation In S13++He Collisions, J. A. Tanis, E. M. Bernstein, M. W. Clark, W. G. Graham, Robert H. Mcfarland, T. J. Morgan, B. M. Johnson, K. W. Jones, M. Meron
Physics Faculty Research & Creative Works
Evidence is presented for a two-step process in ion-atom collisions in which two independent interactions occur in a single encounter. Measurements for 15200-MeVS13++He collisions indicate that uncorrelated projectile K-shell excitation and capture of a target electron occur in a single collision with one target atom. The results are in reasonable qualitative agreement with theoretical predictions of this two-step process. © 1985 The American Physical Society.
A Continental Well-Aged Aerosol In The Guinean Savannah At The Level Of A Trough Along The Itcz, F. Desalmand, Josef Podzimek, R. Serpolay
A Continental Well-Aged Aerosol In The Guinean Savannah At The Level Of A Trough Along The Itcz, F. Desalmand, Josef Podzimek, R. Serpolay
Physics Faculty Research & Creative Works
Simultaneous measurements of Aitken nuclei, cloud condensation nuclei and aerosol particles sizes larger than 0.3 μm in the Guinean savannah during the dry season show an aerosol of very exceptional physical properties: numerous cloud condensation nuclei (2000-3000 per cm3) active at low supersaturation (or slight 'undersaturation'), absence of very small Aitken nuclei active at 180% of supersaturation and concentrations of large aerosol particles (D > 0.3 μm) between 30 and 60 per cm3. The analysis of the aerosol behavior during a 'typical' 24-hr period of the dry season and during a fog situation indicates that (1) the aerosol is a very …
Satellite Structure In Laser-Assisted Charge-Transfer Cross Sections, Y. P. Hsu, Ronald E. Olson
Satellite Structure In Laser-Assisted Charge-Transfer Cross Sections, Y. P. Hsu, Ronald E. Olson
Physics Faculty Research & Creative Works
A six-state coupled-channel calculation has been performed on the laser-assisted charge-transfer collision H++Na+Latin small letter h with stroke. A greatly enhanced charge-transfer cross section is observed for low-energy collisions if the photon energy is matched to the classical satellite frequency. This frequency is determined by the location of an extremum in the difference of potential energies between the laser-pumped initial and final molecular states. The stationary-phase method has been used to reproduce the general features and the magnitude of the cross-section structure. © 1985 The American Physical Society.
The Spin‐Exchange Ferromagnet With Dipole And Quadrupole Interactions, Harry A. Brown
The Spin‐Exchange Ferromagnet With Dipole And Quadrupole Interactions, Harry A. Brown
Physics Faculty Research & Creative Works
No abstract provided.