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Physics Faculty Research & Creative Works

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Articles 1891 - 1920 of 1961

Full-Text Articles in Physical Sciences and Mathematics

Channeltron Gain In Magnetic Fields, Yu Bong Hahn, Robert E. Hebner, Daniel R. Kastelein, Kaare J. Nygaard Dec 1972

Channeltron Gain In Magnetic Fields, Yu Bong Hahn, Robert E. Hebner, Daniel R. Kastelein, Kaare J. Nygaard

Physics Faculty Research & Creative Works

The gain and total count rate of electron channel multipliers depend strongly on applied magnetic fields. We report experimental results for Channeltrons operated in magnetic fields of up to 300 G, and find that the applied voltage must be increased to about 4000 V to maintain a sufficiently high gain. Slightly higher count rates are observed if the magnetic field is parallel to the plane of the Channeltron, as compared to perpendicular to that plane. © 1972 The American Institute of Physics.

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System For Data Acquisition From High Voltage Terminals, George W. York, John T. Park, James J. Miskinis, David H. Crandall, Victor Pol Dec 1972

System For Data Acquisition From High Voltage Terminals, George W. York, John T. Park, James J. Miskinis, David H. Crandall, Victor Pol

Physics Faculty Research & Creative Works

An inexpensive data acquisition system has been designed to provide high voltage isolation for data acquisition in analog, digital, and pulse modes. The telemetry system uses GaAs light sources, fiber optics, and phototransistors to accomplish the data transmission. Prewired logic boards have been adapted to accomplish the timing and logic functions. Seven decades of digital data are transmitted error free, pulse data can be transmitted at rates up to 1 MHz, and analog data are transmitted with 0.05% full scale accuracy. © 1972 The American Institute of Physics.

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Eikonal Approximation For Coupled Equations For Multichannel Scattering, Rung T. Ling, Joseph C.Y. Chen, Jerry Peacher, Kenneth M. Watson Aug 1972

Eikonal Approximation For Coupled Equations For Multichannel Scattering, Rung T. Ling, Joseph C.Y. Chen, Jerry Peacher, Kenneth M. Watson

Physics Faculty Research & Creative Works

It is well known that the Glauber approximation for scattering amplitudes is obtained by applying the eikonal approximation to the Fourier transform of the transition operator. The eikonal approximation can also be applied to the coupled equations of scattering obtained by the expansion of the state function in terms of a suitable set of functions. The scattering amplitude can thus be obtained by solving the set of eikonal coupled equations. The latter approach is analyzed for a special class of channel-coupling potentials. The first-order approximation to the derived eikonal coupled equations is the eikonal Born approximation. Numerical illustrations in this …

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Molecular Model For Prenucleation Water Clusters, P. L. M. Plummer, Barbara N. Hale May 1972

Molecular Model For Prenucleation Water Clusters, P. L. M. Plummer, Barbara N. Hale

Physics Faculty Research & Creative Works

A molecular model applicable to prenucleation water clusters is described. As an illustration the model is applied to water clusters having clathrate-like structures composed of five-menibered rings. This work was motivated by the apparent inadequacies of the corrected liquid drop model which (in addition to applying bulk properties to small clusters) predicts nucleation rates which may be as much as 1017 larger than experiment. We present the "energy of formation" at a temperature of 277°K for our molecular model for clusters ranging in size from 5 to 57 molecules. These results agree qualitatively with experiment and, we believe, provide …

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Thomson's E/M Experiment Revisited, Michael Glascock, Don M. Sparlin Jan 1972

Thomson's E/M Experiment Revisited, Michael Glascock, Don M. Sparlin

Physics Faculty Research & Creative Works

The objective of this experiment is to familiarize the student with the impulse theorem, electron dynamics, and magnetic field contours. He is challenged to obtain accurate as well as precise measurements with suboptimum apparatus through correct analysis. He also investigates the influence of various systematic errors using model calculations on a small computer. © 1972, American Association of Physics Teachers. All rights reserved.

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A Correction To Classical Homogeneous Nucleation Theory For Polar Molecules Exhibiting An Electric Double Layer At The Liquid Surface, Daniel R. White, James L. Kassner Jan 1972

A Correction To Classical Homogeneous Nucleation Theory For Polar Molecules Exhibiting An Electric Double Layer At The Liquid Surface, Daniel R. White, James L. Kassner

Physics Faculty Research & Creative Works

An oriented dipole surface layer is added to the classical liquid drop model of nucleation to account for the surface behavior of substances having polar nonsymmetrical molecules. The preliminary treatment of the change in free energy as given by Abraham is modified to include Fletcher's exponential decay of the degree of orientation. An additional correction for the excess binding energy due to the presence of a foreign molecule in the prenucleation cluster is included to account for the inflections observed in the experimental results of Allen and Kassner. The resulting free energy of formation is combined with the kinetic treatment …

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A Study Of Phosphorus Adsorption And Desorption Kinetics On Silicon (111) Surfaces, L. E. Davis, L. L. Levenson, J. J. Melles Jan 1972

A Study Of Phosphorus Adsorption And Desorption Kinetics On Silicon (111) Surfaces, L. E. Davis, L. L. Levenson, J. J. Melles

Physics Faculty Research & Creative Works

Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) methods were used to characterize the (111) surface of Si wafers before and after the deposition of P2 molecules. Before deposition, the well-known Si(111)-7 LEED pattern was easily obtained by thermal cleaning at 1200 °C. Cleaning was done by electron bombardment in a vacuum chamber with a base pressure of ∼ 10-10 Torr. After cleaning, AES showed that about 10-2 atomic layer of carbon was the only surface contaminant. The sensitivity of our cylindrical AES apparatus for phosphorus was about 10-3 atomic layer. We found that ∼5x10-2 atomic layer of …

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Collisional Excitation Of N+ At 50 Kev, D. H. Crandall, G. York, V. Pol, John T. Park Jan 1972

Collisional Excitation Of N+ At 50 Kev, D. H. Crandall, G. York, V. Pol, John T. Park

Physics Faculty Research & Creative Works

The excitation spectrum of N+ has been observed by examining the energy lost by a 50- keV N+ beam passing through a He target. The spectrum exhibits dramatic features with large cross sections. Determination of the approximate ratio of metastable to ground-state ions in the primary ion beam has permitted measurement of excitation cross sections from both ground-state and metastable N+ ions colliding with He target atoms. © 1972 The American Physical Society.

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Adsorption Of Rare Gas Atoms On Xenon, Donald E. Hagen Jan 1972

Adsorption Of Rare Gas Atoms On Xenon, Donald E. Hagen

Physics Faculty Research & Creative Works

The problem of adsorption of rare gas atoms on solids is treated for the case of submonolayer films. An energy spectrum calculation method which is suitable for band structure or heat capacity calculations is discussed. It is particularly useful for adsorbate-substrate systems in the region intermediate between "tight binding" and "plane wave" behavior. The method employs a technique introduced by Kohn and Luttinger of using the eigenfunctions corresponding to a particular point in the Brillouin zone as a basis set. The cases of He and Ne adsorbed on Xe are discussed.

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An Inexpensive Electrical Vacuum Feedthrough, D. R. Kastelein, Richard A. Anderson, Kaare J. Nygaard Jan 1972

An Inexpensive Electrical Vacuum Feedthrough, D. R. Kastelein, Richard A. Anderson, Kaare J. Nygaard

Physics Faculty Research & Creative Works

No abstract provided.

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Excited-Ion Lifetimes Using Penning-Ionizing Collisions, William F. Parks, Laird D. Schearer Jan 1972

Excited-Ion Lifetimes Using Penning-Ionizing Collisions, William F. Parks, Laird D. Schearer

Physics Faculty Research & Creative Works

We show that in the Penning-ionizing collision He(23S1)+X→He(11S0)+(X+)*+e the precession of the Hem spin at its Larmor frequency forces the J polarization of the Penning ion to rotate at the same frequency but shifted in phase. The tangent of the phase shift is proportional to the lifetime of the ionic state and presents a unique method for measuring excited-ion lifetimes. © 1972 The American Physical Society.

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Application Of The Weiss Molecular Field Theory To The B‐Site Spinel, W. E. Holland, Harry A. Brown Jan 1972

Application Of The Weiss Molecular Field Theory To The B‐Site Spinel, W. E. Holland, Harry A. Brown

Physics Faculty Research & Creative Works

A molecular field treatment of the B‐site spinel was used to determine the ordering temperatures and the asymptotic Curie temperature in terms of the exchange integrals. The theory was developed from a 16‐sublattice model and took into account interactions between an atom and its nearest to fourth‐nearest neighbors. Experimental values of the ordering temperatures and the asymptotic Curie temperature were then used to determine the exchange integrals for the systems Hg1−xCdx Cr2 S4, CdCr2S4(1−y)Se4y, and Zn1−xCdxCr2Se4. Copyright © 1972 WILEY‐VCH Verlag GmbH & Co. KGaA

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Mössbauer-Effect Studies Of The Phase Transitions In Antiferroelectric Pbzro₃ And Ferroelectric Pbti₀.₀₂Zr₀.₈O₃, James P. Canner, C. M. Yagnik, Robert Gerson, William Joseph James Nov 1971

Mössbauer-Effect Studies Of The Phase Transitions In Antiferroelectric Pbzro₃ And Ferroelectric Pbti₀.₀₂Zr₀.₈O₃, James P. Canner, C. M. Yagnik, Robert Gerson, William Joseph James

Physics Faculty Research & Creative Works

The Mössbauer spectra were studied for the antiferroelectric compound PbZrO3 and for the closely related ferroelectric PbTi0.2Zr0.8O3. In both cases, a substitution of 5-mol% BiFeO3 was made to permit the Mössbauer measurements. Little difference was found in the isomer shift in these compounds, whether they were in the ferroelectric, antiferroelectric, or cubic state, indicating that the bonding character is not affected by the transitions among the states. There was a pronounced and approximately equivalent dip in the recoil-free fraction at the Curie points of both the antiferroelectric and ferroelectric materials, associated with …

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Magnetostriction And Magnetic Breakdown In Cadmium, J. M. Carter, Don M. Sparlin Jan 1971

Magnetostriction And Magnetic Breakdown In Cadmium, J. M. Carter, Don M. Sparlin

Physics Faculty Research & Creative Works

Studies of the monotonic magnetostriction of cadmium at 4.2 °K in applied magnetic fields to 70 kG have shown that the angular variation of an extremal point Hm is proportional to secθ. The magnitude of Hm is in close agreement with the onset of a breakdown orbit γ13 observed for the applied field within 35 °of the c axis. The range of observation of Hm coincides with the range of the orbit γ. © 1971 The American Physical Society.

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Scattering Of Waves In Many Dimensions, I. Adawi Jan 1971

Scattering Of Waves In Many Dimensions, I. Adawi

Physics Faculty Research & Creative Works

Scattering by a spherical potential is discussed in all dimensions by one formulation using the partial-wave expansion method. The optical theorem relating the total scattering cross section σ to the forward scattering amplitude f(0) is derived.

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Collision Cross Sections For The Excitation Of The Schumann-Runge Dissociation Continuum In Molecular Oxygen By 20-110-Kev Protons, John T. Park, F. D. Schowengerdt, D. R. Schoonover Jan 1971

Collision Cross Sections For The Excitation Of The Schumann-Runge Dissociation Continuum In Molecular Oxygen By 20-110-Kev Protons, John T. Park, F. D. Schowengerdt, D. R. Schoonover

Physics Faculty Research & Creative Works

Absolute cross sections for the excitation of the Schumann-Runge dissociation continuum of molecular oxygen have been obtained from inelastic energy-loss spectra induced by 20-110-keV protons incident on gaseous targets of molecular oxygen. Apparent differential energy loss cross sections, ionization cross sections, and total inelastic cross sections are also obtained from the energy-loss spectra. The proton energy-loss spectra have an energy resolution of about 2 eV. The energy location of the first peak in the energy-loss spectra of O2 is in general agreement with the findings of photo absorption and electron energy-loss-spectra measurements. The cross section for the Schumann-Runge dissociation continuum …

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Second- And Third-Order Elastic Constants Of Aluminum And Lead, Tetsuro Suzuki Jan 1971

Second- And Third-Order Elastic Constants Of Aluminum And Lead, Tetsuro Suzuki

Physics Faculty Research & Creative Works

The second- and third-order elastic constants of Al and Pb are calculated as the second and third derivatives of the binding energy with respect to the finite deformation parameter. The binding energy is derived from a local pseudopotential by use of second-order perturbation theory. It is shown that the binding energy satisfied not only the diagonal equilibrium condition, but also the off-diagonal equilibrium condition, i.e., the first derivative of the binding energy with respect to a volume change as well as with respect to shear deformations is zero. Accordingly, the present method of calculation is based on a stable lattice …

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Calculation Of Anisotropic Hyperfine Constants For Lattice Nuclei Near A Shallow Donor, Edward B. (Boyd) Hale, Robert Lee Mieher Jan 1971

Calculation Of Anisotropic Hyperfine Constants For Lattice Nuclei Near A Shallow Donor, Edward B. (Boyd) Hale, Robert Lee Mieher

Physics Faculty Research & Creative Works

A method is presented for calculating the magnetic anisotropic (dipolar) hyperfine constants for lattice nuclei near a shallow-donor impurity. The method assumes that the wave function of the donor electron can be expressed in an effective-mass form, i.e., a slowly varying envelope function times conduction-band Bloch functions. For each dipolar hyperfine constant, two separate calculations are performed. One calculation is for a local region about the lattice nucleus of interest. The greatest part of the interaction occurs in this region (about 85 ± 10%). The second calculation is for the more distant region. The dipolar constants in the distant region …

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Electron-Impact Excitation Of Auto-Ionizing Levels In Cesium, Yu Bong Hahn, Kaare J. Nygaard Jan 1971

Electron-Impact Excitation Of Auto-Ionizing Levels In Cesium, Yu Bong Hahn, Kaare J. Nygaard

Physics Faculty Research & Creative Works

Auto-ionizing states in Cs between 12 and 20 eV have been studied by electron impact. The retarding-potential-difference method was used to obtain an electron beam with energy spread of about 0.1 eV. To determine the threshold energies, inelastically scattered electrons were analyzed by the trapped-electron method. We have been able to identify about 20 levels, and the agreement with spectroscopic data is excellent. A peak appearing at 12.80 eV is probably due to the quartet states observed by Feldman and Novick. © 1971 The American Physical Society.

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Experimental And Theoretical Study Of The Sign Preference In The Nucleation Of Water Vapor, Daniel R. White, James L. Kassner Jan 1971

Experimental And Theoretical Study Of The Sign Preference In The Nucleation Of Water Vapor, Daniel R. White, James L. Kassner

Physics Faculty Research & Creative Works

The nucleation of water vapor on ions in atmospheres of helium and argon was studied using an expansion type cloud chamber. Separation of the positive and negative ions was achieved so that the nucleation could be studied as a function of both the sign of the ionic charge and the supersaturation. A semiphenominological theory was developed as an extension of the classical liquid drop theory to include the effects of the ionic charge on the nucleation process. The theoretical model of the prenucleation embryo was assumed to possess an oriented dipole surface layer with the direction of orientation dependent on …

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Excitation Of The 2s State Of Atomic Hydrogen By Electron Impact In The Distorted-Wave Approximation - Angular Distributions, W. Neil Shelton, E. S. Leherissey, Don H. Madison Jan 1971

Excitation Of The 2s State Of Atomic Hydrogen By Electron Impact In The Distorted-Wave Approximation - Angular Distributions, W. Neil Shelton, E. S. Leherissey, Don H. Madison

Physics Faculty Research & Creative Works

The excitation of ground-state hydrogen atoms to the 2s state by the impact of electrons with energies of 1 to 50 Ry (13.6 to 680.3 eV) has been calculated in the distorted-wave approximation with exchange included. The angular distributions of the scattered electrons at 1 and 4 Ry are compared with those derived from the close-coupling calculations by Burke, Schey, and Smith, and are compared with four different plane-wave theories at all energies calculated. Taking the close-coupling results as a standard, it is found that the distorted-wave angular distributions represent an improvement over those of the plane-wave theories.

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Mössbauer Studies Of Bifeo₃-Pbtio₃ Perovskite-Type Solid Solutions, C. M. Yagnik, Robert Gerson, William Joseph James Jan 1971

Mössbauer Studies Of Bifeo₃-Pbtio₃ Perovskite-Type Solid Solutions, C. M. Yagnik, Robert Gerson, William Joseph James

Physics Faculty Research & Creative Works

The Mössbauer spectra of the ferroelectric solid solutions (BiFeO3)x(PbTiO)1-x have been studied as a function of temperature, mainly between room temperature and 600°C, using 57Fe in the solutions as an absorber. The quadrupole splitting increased and the isomer shift decreased between x = 0.05 and x = 0.70, a range in which the solutions are tetragonal and paramagnetic, and in which the unit cell volume increases with increasing x. The isomer shift, in particular, was primarily determined by the unit cell volume. Data are presented on the internal magnetic field of the antiferromagnetic …

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Absolute Excitation Cross Sections Of He+ In 20-100-Kev He+-He Collisions Using Energy-Loss Spectrometry, D. R. Schoonover, John T. Park Jan 1971

Absolute Excitation Cross Sections Of He+ In 20-100-Kev He+-He Collisions Using Energy-Loss Spectrometry, D. R. Schoonover, John T. Park

Physics Faculty Research & Creative Works

Application of positive-ion energy-loss spectrometry has been extended to include experimental determination of absolute excitation cross sections of ground-state helium ions. Helium ion-atom collisions were studied for impact energies ranging between 20-100 keV, in 10-keV intervals. The data were taken with an apparatus resolution between 0.6-0.8 eV full width at half-maximum (FWHM). Cross sections for transitions from ground state to the second and third principal quantum levels of the ion plotted as a function of impact energy were still rapidly increasing at 100 keV. The cross sections at this energy were (1.64 ± 0.28) x 10-18 cm2 for He+(1s122)→He+ (n=2) …

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Heisenberg Ferromagnet With Biquadratic Exchange, Harry A. Brown Jan 1971

Heisenberg Ferromagnet With Biquadratic Exchange, Harry A. Brown

Physics Faculty Research & Creative Works

The usual Heisenberg Hamiltonian with bilinear exchange -2JS→1•S→2 has been extended to include a biquadratic term -2αJ(S→1•S→2)2, with an adjustable parameter α. A method equivalent to constant coupling was employed to calculate the effect of the biquadratic exchange term on the Curie temperature, magnetization, susceptibility, specific heat, and entropy for lattices with spin-1 atoms. As α goes from 0 to 1, the Curie temperature falls by a factor 2 to 3, while the asymptotic Curie temperature is reduced by the factor 2. The magnetization rises much more rapidly below TC, and the specific heat has a peak and discontinuity several …

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Surface Plasmons And The Reflectivity Of N-Type Insb, William E. Anderson, Ralph William Alexander, Robert John Bell Jan 1971

Surface Plasmons And The Reflectivity Of N-Type Insb, William E. Anderson, Ralph William Alexander, Robert John Bell

Physics Faculty Research & Creative Works

The Reflectivity of N-Type InSb Has Been Measured in the Far Infrared. the Doping of the Samples Was Such that the Free-Carrier Plasma Frequency Was Near the LO Mode Frequency. the Results Suggest that Samples with a Sufficiently Thick Damage Layer Show Effects Due to Surface Plasmons. Use of a Simple Model Indicates that the Surface-Plasma Excitations Are Coupled to the Phonons. © 1971 the American Physical Society.

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Doppler Shift In Frequency In The Transport Of Electromagnetic Waves Through An Underdense Plasma, Jerry Peacher, Kenneth M. Watson Oct 1970

Doppler Shift In Frequency In The Transport Of Electromagnetic Waves Through An Underdense Plasma, Jerry Peacher, Kenneth M. Watson

Physics Faculty Research & Creative Works

In an earlier publication, the validity of the radiation transport theory was studied for the calculation of multiple scattering of electromagnetic waves by a turbulent plasma. In the present paper, we extend the transport theory to include a description of the Doppler shift in frequency caused by electron motion.

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Differential Cross Section For Charged A₁ Photoproduction Using The Regge Exchange Formalism, Keiji Kikkawa, Barbara N. Hale Feb 1970

Differential Cross Section For Charged A₁ Photoproduction Using The Regge Exchange Formalism, Keiji Kikkawa, Barbara N. Hale

Physics Faculty Research & Creative Works

The Regge-pole formalism is applied to the calculation of the differential cross section for A1+ photo-production in the region |tmin| < -t < 10µ2. The p, A1, A1-daughter, A2, and π trajectory contributions are considered, and use is made of chiral dynamics to estimate the unknown coupling constants. We find that the π and the A2 trajectories provide the dominant contributions.

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Note On "Approximate Free Energies For Heisenberg Ferromagnets", J. H. Hemmann, Harry A. Brown Jan 1970

Note On "Approximate Free Energies For Heisenberg Ferromagnets", J. H. Hemmann, Harry A. Brown

Physics Faculty Research & Creative Works

No abstract provided.

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Ground-State Wave Function Of Shallow Donors In Uniaxially Stressed Silicon: Piezohyperfine Constants Determined By Electron-Nuclear Double Resonance, Edward B. (Boyd) Hale, Theodore G. Castner Jan 1970

Ground-State Wave Function Of Shallow Donors In Uniaxially Stressed Silicon: Piezohyperfine Constants Determined By Electron-Nuclear Double Resonance, Edward B. (Boyd) Hale, Theodore G. Castner

Physics Faculty Research & Creative Works

Stress-induced changes in the ENDOR spectra of a shallow donor electron interacting with various Si29 nuclei neighboring the donor have been experimentally and theoretically investigated. For each of the three measured donors - As, P, and Sb - the compressional, uniaxial stress was applied along the [001] axis and its magnitude corresponded to strains up to 10-3. To describe the observed linear and quadratic shifts and splitting's of the lines in an ENDOR shell, we have defined a set of piezo hyperfine constants. One piezo hyperfine constant was measured for each axis-class shell; three independent piezo hyperfine constants were measured …

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Theory Of Droplet Growth In Clouds. I. The Transient Stage Of The Boundary-Coupled Simultaneous Heat And Mass Transport In Cloud Formation, John C. Carstens, Joseph T. Zung Jan 1970

Theory Of Droplet Growth In Clouds. I. The Transient Stage Of The Boundary-Coupled Simultaneous Heat And Mass Transport In Cloud Formation, John C. Carstens, Joseph T. Zung

Physics Faculty Research & Creative Works

Two solutions to the system of equations describing the simultaneous heat and mass transport involved in the condensational growth of a droplet in a supersaturated atmosphere are presented. The first, valid for very short times, describes the transient stage of such growth; the second, valid for longer times, presupposes the establishment of a steady-state condition. The two are shown to be complementary for the cases examined. The equations examined satisfy the usual boundary conditions imposed on a drop in a concentric sphere as required by the cellular model for cloud formation. Hence our results can be immediately extended to the …

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