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1971

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Articles 1 - 30 of 49

Full-Text Articles in Physics

Shubnikov-De Haas Effect And Magnetic Breakdown In Be , David J. Sellmyer, I.S. Goldstein, B.L. Averbach Dec 1971

Shubnikov-De Haas Effect And Magnetic Breakdown In Be , David J. Sellmyer, I.S. Goldstein, B.L. Averbach

David Sellmyer Publications

Magnetic breakdown in the basal plane of Be was investigated in fields up to 150 kG. Geometrical aspects of the open orbits caused by breakdown are discussed. An estimate of 30 kG for the characteristic breakdown field is obtained by applying the theory of Falicov et al. Shubnikov-de Haas frequency measurements are reported for the central-cigar cross section. These measurements are relevant to a recent conjecture that the Onsager-Lifshitz quantization scheme may be violated in the presence of magnetic breakdown.

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Even-Parity Lattice Resonances And Anharmonicity In Ki: Ag+, Roger D. Kirby Nov 1971

Even-Parity Lattice Resonances And Anharmonicity In Ki: Ag+, Roger D. Kirby

Roger Kirby Publications

We report here the observation of four impurity-induced lattice resonances in KI:Ag+. In addition to the well-known T1u symmetry resonant mode at 17.3 cm-1, we have observed two even-parity resonant modes of A1g and Eg symmetries at 25 and 16.35 cm-1, respectively, and a T1u symmetry gap mode at 86.2 cm-1. The two even-parity modes were detected using far-infrared spectroscopic techniques with the sample in an external electric field. The field induces a strong mixing of the modes of opposite parity and results in large field-induced shifts. The Eg symmetry resonance has also been seen in the Raman spectrum of …

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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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Thermionic Space Charge Oscillations, William Carl Nov 1971

Thermionic Space Charge Oscillations, William Carl

Masters Theses & Specialist Projects

Thermionic electrons emitted into a potential well will produce radiation, the frequency of which is determined by the transit time of the electrons. This paper investigates the case where radiation is produced by a vacuum tube in which two Pierce guns face each other, one acting as the emitter, the other acting as a reflector. Symmetry and the focusing of the electron beam by the Pierce guns make it possible to make an accurate determination of the electron transit time. Measurements showed that the period of the oscillation was 1.5 times the period required for an electron to traverse the …

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Cellular Inactivation By Heavy Ions, Neutrons, And Pions, Robert Katz, S. C. Sharma, M. Hamayoonfar Oct 1971

Cellular Inactivation By Heavy Ions, Neutrons, And Pions, Robert Katz, S. C. Sharma, M. Hamayoonfar

Robert Katz Publications

The delta-ray theory of the inactivation of cells by energetic heavy ions describes cellular survival after heavy ion bombardment through a two-component survival model, in which 4 operational parameters (E0,m0, σ0, and κ) describe the response of a particular cellular variety in a particular ambient condition, for an arbitrary radiation environment. The quantities m and E0 are the extrapolation number and extrapolated D-37 dose of the survival curve after gamma-ray irradiation. The quantities σ0 and κ are found from the initial slope of survival curves after irradiation with ions of different LET, …

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Measurement Of Currents In Lake Mead With The Deep Water Isotopic Current Analyzer (Dwica), J. J. Sartoris, D. A. Hoffman, Bureau Of Reclamation Oct 1971

Measurement Of Currents In Lake Mead With The Deep Water Isotopic Current Analyzer (Dwica), J. J. Sartoris, D. A. Hoffman, Bureau Of Reclamation

Publications (WR)

In Nov 1967, a Deep Water Isotopic Current Analyzer (DWICA) was used to study current patterns in the Boulder Basin of Lake Mead to determine if low-quality water from Las Vegas Bay might enter the Southern Nevada Water Project intake on Saddle Island. Secondary objectives were to study the general current patterns in Boulder Basin and the effect of power discharges at Hoover Dam on these currents. Results of current measurements at 3 stations in Boulder Basin are given. Observations indicate a definite possibility that low-quality water from Las Vegas Bay might enter the water intake on Saddle Island. Current …

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Nuclear-Magnetic-Resonance Studies Of The Semiconductor-To-Metal Transition In Chlorine-Doped Cadmium Sulfide, Frank D. Adams, David C. Look, Carlton L. Brown, Donald R. Locker Oct 1971

Nuclear-Magnetic-Resonance Studies Of The Semiconductor-To-Metal Transition In Chlorine-Doped Cadmium Sulfide, Frank D. Adams, David C. Look, Carlton L. Brown, Donald R. Locker

Physics Faculty Publications

Spin-lattice relaxation times (T1) and Knight shifts were measured for Cd113 nuclei in 12 CdS crystals doped with various amounts of chlorine. Hall coefficients were measured in order to estimate conduction-electron concentrations. Data were obtained for all samples at 300 °K and for some highly doped samples at 77, 4.2, and 2.13 °K. Metallic properties were observed in all samples having electron concentrations n>2×1018 cm-3. At 300 °K, we find 1/T1∝n for nonmetallic samples and 1/T1∝n2/3 when samples are metallic. The latter proportionality continues to hold at lower …

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Comment On Electron Scattering In The Image Potential Well, Pavel Smejtek, M. Silver Oct 1971

Comment On Electron Scattering In The Image Potential Well, Pavel Smejtek, M. Silver

Physics Faculty Publications and Presentations

Comments are made on the model of electron injection into SiO₂ proposed by Berglund and Powell. Their assumptions on electron scattering, disregarding the change of the escape cone with the distance from the emitter, lead to serious underestimation of the injected current. Two alternative models of electron injection, based solely on elastic scattering are discussed and do not predict the experimental results. We suggest that observed field dependence of the injected current into SiO₂ indicates that energy relaxation associated with the injected electrons is responsible for the voltage dependence of the current.

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Studies Of The Potential Curve Crossing Problem I. Analysis Of Stueckelberg's Method, W. R. Thorson, John B. Delos, Seth A. Boorstein Sep 1971

Studies Of The Potential Curve Crossing Problem I. Analysis Of Stueckelberg's Method, W. R. Thorson, John B. Delos, Seth A. Boorstein

Arts & Sciences Articles

A detailed critical analysis is made of Stueckelberg's treatment of inelastic transitions at a crossing of two potential curves. Using an asymptotic method analogous to the WKB approximation, Stueckelberg obtained the well-known Landau-Zener-Stueckelberg (LZS) formula for the inelastic transition probability. His method involved the determination of "connection formulas" linking amplitudes associated with his asymptotic approximants on either side of the crossing-point region. Here we show that (a) Stueckelberg's asymptotic approximants are just the WKB approximants for elastic scattering on the adiabatic (noncrossing) potential curves; (b) Stueckelberg's method for obtaining the connection formulas can be put on a rigorous footing, including …

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Application Of The Method Of Lattice Statics To Vacancies In Aluminum, Larry Boyer, John R. Hardy Aug 1971

Application Of The Method Of Lattice Statics To Vacancies In Aluminum, Larry Boyer, John R. Hardy

John R. Hardy Papers

In this paper the method of lattice statics is applied to the calculation of the atomic displacements about a vacancy in aluminum using a fifth-neighbor force-constant model for the dynamical matrix and the vacancy-host lattice interaction. The strain-field interaction energy between two vacancies is similarly calculated. The main object of this work is to demonstrate the important modifications of earlier results, obtained for a first- and second-neighbor force-constant model, when one uses the fifth-neighbor model designed to give a significantly better fit to the measured phonon dispersion curves. In particular it is demonstrated that the displacements about the vacancy continue …

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On The Molecular Theory Of Dielectric Polarization In Rigid‐Dipole Fluids, John D. Ramshaw Aug 1971

On The Molecular Theory Of Dielectric Polarization In Rigid‐Dipole Fluids, John D. Ramshaw

Physics Faculty Publications and Presentations

A molecular theory is developed for the polarization P(r) produced by a weak position‐dependent external electric field E0(r) in a finite fluid system, of arbitrary shape, composed of rigid polar molecules. The theory differs from earlier work in that no assumption is made concerning the form of the electrostatic constitutive relation. [The usual assumption in this regard is that P(r) = (ε–1) E(r) / 4π, where E(r) is the total Maxwell electric field. The “dielectric constant” ε is well defined only if the relation between P(r) and E(r) …

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High-Pressure Equation Of State For Nacl, Kcl, And Cscl, Daniel L. Decker Jul 1971

High-Pressure Equation Of State For Nacl, Kcl, And Cscl, Daniel L. Decker

Faculty Publications

A calculation of the equation of state for NaCl from a Mie-Grüneisen equation was repeated using more accurate values of the zero-pressure compressibility. It was also extended to KCl and CsCl. An analysis of this approach to pressure calibration indicates that it will yield pressures with about the same accuracy as can be presently achieved by experimental measurements above 25 kbar, and thus furnishes a temporary practical pressure scale.

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Raising Of Discrete Levels Into The Far Continuum, J.L. Dehmer, Anthony F. Starace, U. Fano, J. Sugar, J.W. Cooper Jun 1971

Raising Of Discrete Levels Into The Far Continuum, J.L. Dehmer, Anthony F. Starace, U. Fano, J. Sugar, J.W. Cooper

Anthony F. Starace Publications

Broad peaks observed in the photoabsorption spectra of rare earths ∼10-20 eV above the 4d edge are attributed to transitions 4d104fN→4d94fN+1. Exchange interaction splits the 4d94fN+1 configuration and raises some multiplets by ∼20 eV. Autoionization to 4d9-4fNεf broadens the high levels. The interpretation extends to p→d processes observed in the absorption of synchrotron light by transition elements.

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Calculation Of Point-Defect Energies And Displacements In Alkali Halides Using The Lattice-Statics Method, Arnold Karo, John Hardy May 1971

Calculation Of Point-Defect Energies And Displacements In Alkali Halides Using The Lattice-Statics Method, Arnold Karo, John Hardy

John R. Hardy Papers

The method of lattice statics, in the zero-order approximation, is used to evaluate the Schottky-pair formation energies and the displacement fields about positive- and negative-ion vacancies for all alkali halide crystals with rock-salt structures. The deformation-dipole model, used extensively in earlier work on the lattice dynamics of these crystals, is employed to describe the host lattice. Long-range Coulomb interactions are included explicitly, and short-range repulsive interactions are described by a simple Born-Mayer potential. Comparison is made with earlier Mott-Littleton-type calculations and very satisfactory agreement is found. Comparison with available experimental values is somewhat less satisfactory, particularly regarding the lithium salts; …

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Ion‐Pair Theory Of Concentrated Electrolytes. Iii. Variational Principle, Frank Stillinger, Ronald White Apr 1971

Ion‐Pair Theory Of Concentrated Electrolytes. Iii. Variational Principle, Frank Stillinger, Ronald White

Center for Advanced Mineral and Metallurgical Processing (CAMP)

Two major contributions are devised for that theory of concentrated electrolytes which by convention regards the ions as completely paired into uncharged dipolar “molecules.” First, a more satisfactory expression is obtained for the wavelength‐dependent static dielectric “constant” ε(k). Second, a variational principle for Helmholtz free energy F is displayed whose minimization with respect to the ion‐pair size distribution p(1) serves to determine both F and p(1). In anticipation of future numerical applications, a binary collision approximation is specified for the short‐range interaction aspect of the functional F[p(1)].

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Ion‐Pair Theory Of Concentrated Electrolytes. Iv. Ion Atmosphere Charge Distribution, Frank Stillinger, Ronald White Apr 1971

Ion‐Pair Theory Of Concentrated Electrolytes. Iv. Ion Atmosphere Charge Distribution, Frank Stillinger, Ronald White

Center for Advanced Mineral and Metallurgical Processing (CAMP)

Arguments are presented indicating that the large‐size limiting behavior of the ion‐pair size distribution is qualitatively the same both with, and without, Coulomb interactions between ions. This in turn implies that the static dielectric response function ε0 / ε(k) derived in the preceding paper is nonanalytic at k = 0. The specific singular behavior of this response requires a branch cut along the imaginary k axis. It furthermore induces an r−8 tail in the ion atmosphere charge distribution at finite electrolyte concentration.

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Length And Velocity Formulas In Approximate Oscillator-Strength Calculations, Anthony F. Starace Apr 1971

Length And Velocity Formulas In Approximate Oscillator-Strength Calculations, Anthony F. Starace

Anthony F. Starace Publications

The matrix element for electric dipole transitions is correctly given by the length formula in the Hartree-Fock, configuration-interaction, and related approximations, which involve the diagonalization of an approximate, but nonlocal, Hamiltonian.

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Mössbauer Spectroscopy Study Of The Spin‐Flop Transition In Fe‐Doped Mnf2, C. R. Abeledo, Richard B. Frankel, A. Misetich, N. A. Blum Mar 1971

Mössbauer Spectroscopy Study Of The Spin‐Flop Transition In Fe‐Doped Mnf2, C. R. Abeledo, Richard B. Frankel, A. Misetich, N. A. Blum

Physics

Measurements of the hyperfine interaction in Fe+ + in MnF2 in external fields above the spin‐flop field at 4.2 K are reported and a value of g⊥ = 2.13 is derived, in good agreement with theory.

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Track Theory And Radiation Quality, Robert Katz Mar 1971

Track Theory And Radiation Quality, Robert Katz

Robert Katz Publications

Radiation detection and damage data from several physical, chemical, and biological systems have been analyzed by a unified track theory, in which observed effects are attributed to the interaction of secondary electrons with the medium. Gamma-ray dose-response curves are combined with calculations of the spatial dose distribution about an ion's path to yield dose-response curves (survival curves) for heavy ion bombardment, through appropriately defined parameters. Perplexing phenomena associated with high LET radiation are sorted out according to track regime (grain-count or track-width), inactivation mode (gamma-kill or ion-kill), structural complexity (elementary, cellular, multicellular), and end-point. The central problem in assigning a …

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Mössbauer Effect In Fe-Doped Kmgf3, J. Chappert, J. R. Regnard, Richard B. Frankel, A. Misetich, N. A. Blum Mar 1971

Mössbauer Effect In Fe-Doped Kmgf3, J. Chappert, J. R. Regnard, Richard B. Frankel, A. Misetich, N. A. Blum

Physics

An iron-doped KMgF3 single crystal has been studied with the Mössbauer technique. The two charge states, Fe2+ and Fe3+, are observed. Below 12 °K an Fe2+ quadrupole doublet appears. Using Ham strain model we calculate that the first excited spin-orbit level lies ~ 120 cm-1 above the Γ5g ground state.

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Low-Lying Even-Parity Resonances In Ki:Ag+, Roger D. Kirby Mar 1971

Low-Lying Even-Parity Resonances In Ki:Ag+, Roger D. Kirby

Roger Kirby Publications

Lattice resonances of Eg symmetry (16.35 cm-1) and A1g symmetry (25 cm-1) have been found in KI:Ag+ using far-infrared spectroscopic techniques. The two even-parity modes are found to be anharmonically coupled to the T1u- symmetry resonant mode at 17.3 cm-1, giving rise to the combination bands observed at 30 and 44.4 cm-1.

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Isomeric Shift Of The 83 Kev Transition In 153Eu, E. Ansaldo, L. Grodzins, Richard B. Frankel Feb 1971

Isomeric Shift Of The 83 Kev Transition In 153Eu, E. Ansaldo, L. Grodzins, Richard B. Frankel

Physics

No abstract provided.

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Far-Infrared Properties Of Lattice Resonant Modes. V. Second-Order Stark Effect, B.P. Clayman, Roger D. Kirby, A. J. Sievers Feb 1971

Far-Infrared Properties Of Lattice Resonant Modes. V. Second-Order Stark Effect, B.P. Clayman, Roger D. Kirby, A. J. Sievers

Roger Kirby Publications

Small electric-field-induced frequency shifts have been observed for resonant modes associated with three defect systems. For NaI: Clˉ, the shifts have been used to measure the quartic anharmonic terms of the interionic potential of the impurity ion. For KBr: Li+, the quartic anharmonic terms are found to be very small, and an harmonic potential which includes a central barrier with the barrier height less than the zero-point energy of the oscillator is required to explain the experimental results. For NaCl: Cu+, only an "on-center" resonant-mode configuration is consistent with the experimental results.

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Simulation Of Particle Tracks In Emulsion, Thomas E. Furtak, Robert Katz Feb 1971

Simulation Of Particle Tracks In Emulsion, Thomas E. Furtak, Robert Katz

Robert Katz Publications

Micrographs of energetic particles in nuclear emulsion are simulated by computing the spatial distribution of developed grains with the δ-ray theory of track structure, and representing the developed grains by points of light on an IBM 2250 visual display unit. The simulated tracks display many of the features of actual track structure and serve as a visual comparison between experiment and theory,

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Lamb-Mössbauer Factor Of Sodium Ferrocyanide, Daniel L. Decker, L. E. Lortz Feb 1971

Lamb-Mössbauer Factor Of Sodium Ferrocyanide, Daniel L. Decker, L. E. Lortz

Faculty Publications

Using a set of commercially prepared sodium ferrocyanide absorbers enriched to 91.2% Fe57 the Lamb-Mössbauer factor was measured to be 0.28±0.03. The thickness of Fe57 for these absorbers was measured using x-ray absorption techniques and was found to be considerably smaller than that advertised by the manufacturer even after correcting for the size of the ferrocyanide particles in the absorbers.

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Dielectric Polarization And Alignment And The Structure Of Polar Fluids, John D. Ramshaw, D. W. Schaefer, John S. Waugh, J. M. Deutsch Feb 1971

Dielectric Polarization And Alignment And The Structure Of Polar Fluids, John D. Ramshaw, D. W. Schaefer, John S. Waugh, J. M. Deutsch

Physics Faculty Publications and Presentations

An analysis is made of the information about the structure of dense polar fluids which resides in the dielectric constant, the Kerr constant, and the nuclear magnetic resonance (NMR) quadratic electric field effect. The inadequacy of the "local-field" model for liquids is discussed. The existence of a nonzero molecular hyperpolarizability is shown to destroy an equivalence which would otherwise exist between the Kerr and NMR experiments, and can easily account for apparent discrepancies between the reported Kerr and NMR data for nitrobenzene and nitromethane. A method is presented for removing dielectric boundary effects from statistical averages, so that the averages …

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Theory Of Relativistic Magnetic Dipole Transitions: Lifetime Of The Metastable 2s3 State Of The Heliumlike Ions, Gordon W. F. Drake Jan 1971

Theory Of Relativistic Magnetic Dipole Transitions: Lifetime Of The Metastable 2s3 State Of The Heliumlike Ions, Gordon W. F. Drake

Physics Publications

It has recently been established that the radiative lifetime of the metastable 2S3 state of helium and the heliumlike ions is determined by single-photon magnetic dipole (M1) transitions to the ground state, rather than the two-photon process proposed by Breit and Teller. The theory of nl-n′l M1 transitions with n ′ is developed in the Pauli approximation and extended to two-electron systems. Terms arising from relativistic energy corrections and finite-wavelength effects are included. The results for hydrogenic systems are shown to be identical to those obtained in the relativistic four-component Dirac formulation. The coefficients in the Z-1 perturbation expansion of …

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Mossbauer Study Of An Intramolecular Antiferromagnet, R. Lechan, C. R. Abeledo, R. B. Frankel Jan 1971

Mossbauer Study Of An Intramolecular Antiferromagnet, R. Lechan, C. R. Abeledo, R. B. Frankel

Physics

Mossbauer measurements at 4.2 ≤T ≤ 22 K and OsHosBO kOe are + reported in (Fe Salen Cl)2, a molecular complex containing two coupled Fe3+ ions bridged by oxygen atoms. At 4.2 K only the ground state with effective spin S = 0 is appreciably populated. Analysis of the magnetic field and temperature dependence of the magnetic hyperfine field yields an exchange constant J= -6.7 cm>sup>-1 and a hyperfine field of -192 kOe per unit spin at each Fe3+ nucleus.

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Local Magnetic Moments And The Mossbauer Effect, Richard B. Frankel, Brian B. Schwartz Jan 1971

Local Magnetic Moments And The Mossbauer Effect, Richard B. Frankel, Brian B. Schwartz

Physics

No abstract provided.

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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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