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Journal of Applied Physics

Issue 12 • Date Dec 1957

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Displaying Results 1 - 25 of 32
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Editorial: Robert L. Sproull

    Page(s): 1387
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    First Page of the Article
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  • Structure in Magnetically Confined Electron Beams

    Page(s): 1388 - 1397
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    A number of observations have been made of structure changes that occur in hollow and solid electron beams which are confined by a magnetic field. These structure changes occur in both the density of the beam and the transverse velocity components of the beam electrons. The velocity components have been measured by use of a pinhole camera. Some of the results obtained are as follows. The density of electron paths in a beam may become non‐uniform if there is a spread in the forward component of velocity of the electrons. This may occur either because of a spread in initial angle of the electrons or because of a potential depression in the beam. In addition, changes in beam shape and transverse velocity components of the beam electrons can occur as a result of drifting of electrons in crossed electric and magnetic fields, the electric fields in this case being provided by the space charge of the electrons themselves. Thin beams have been found to be unstable and it has been observed that they divide into an array of vortex‐like current filaments when the beam current is sufficiently high. A possible connection between this occurrence and phenomena in the aurora is suggested. View full abstract»

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  • Electron Emission in Moderate Accelerating Fields

    Page(s): 1398 - 1405
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    Investigations of Schottky emission from metals, including some recent work, are summarized and discussed. The following are some of the conclusions: The surface barrier outside a uniform metal surface can be represented accurately by a mirror‐image form for distances greater than about 20 A from the surface. Patch effects can be correlated to some extent with known surface properties. The dependence of photoelectric emission on applied field is in agreement with the Fowler theory adjusted for a Schottky‐type field‐dependent threshold. Periodic deviations from the thermionic Schottky effect are in full agreement with the mirror‐image model for the extra‐surface barrier, and can be used in determining the barrier form in the immediate vicinity of the emitter surface. View full abstract»

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  • Transmission of Electrons through Metal Surfaces

    Page(s): 1405 - 1408
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    This paper is a review of recent developments in the theory of electron emission from metals. The main subjects discussed are the periodic deviations in the Schottky effect and the transition between thermionic and field emission. The indications are that each of these phenomena can be understood in terms of the free electron model for the metal and the transmission of the electrons through the image force barrier at the metal surface. View full abstract»

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  • Application of the Mass Spectrometer to the Study of the Upper Energy States of Molecules

    Page(s): 1409 - 1413
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    It is claimed that the poor agreement often found between the energy quantities measured by mass spectrometry, and those obtained by other methods, is due in large part to the interpretation of the experimental data. The conditions necessary for accurate measurement are summarized. It is shown that by making certain assumptions about the probability of ionization for different processes, ionization efficiency curves can be interpreted to give the probabilities for electronic transitions from the ground state to the various ionic states of molecules. From these electronic transition probabilities, information can be deduced about the potential energy functions for these upper states. To exploit the method fully, beams of ionizing particles with low spreads in energy are necessary. Electron and photon impact are compared, and it is shown that the latter possesses many advantages. View full abstract»

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  • Formation of Negative Ions in Gases by Secondary Collision Processes

    Page(s): 1414 - 1418
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    Experiments on the formation of negative ions by electron bombardment of hydrogen, oxygen, and water vapor at pressures of 0–4 mm are described. The only ion observed in hydrogen is H-, formed by dissociative attachment. Pressure dependence of the O2- intensity shows that a secondary collision is involved in its formation. Data on the formation of O- and O2- at low electron energies indicate that the secondary collision leading to the formation of O2- does not involve an O- ion. The formation of O2- probably involves a stabilizing collision with a molecule of gas after the initial formation of the ion by electron attachment. From the behavior of H-, O-, and OH- intensities with H2O pressure, it is shown that the secondary process for the formation of OH- in water vapor is probably H-+H2OOH-+H2. The cross section for this reaction is more than 10-17 cm2. View full abstract»

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  • Effect of Oxygen on Etch‐Pit Formation in Silicon

    Page(s): 1419 - 1423
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    The etching behavior of as‐grown and heat‐treated silicon crystals has been studied using an etching procedure developed by Dash. The rate of chemical etching of silicon was found to decrease with increased concentration of dissolved oxygen. This effect impedes the formation of etch‐pits. To explain the observed etching behavior after heat treatment it is necessary to assume that the rate of chemical etching increases with increased amount of precipitated oxygen in pulled crystals. View full abstract»

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  • Lifetime in Pulled Silicon Crystals

    Page(s): 1423 - 1426
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    Lifetime data of 46 pulled silicon crystals are interpreted in terms of the Shockley‐Read recombination theory. The data are consistent with the theory under the assumption of a single recombination level and a constant concentration of recombination centers, independent of the resistivity of the crystals. However, it is not possible to distinguish between two possibilities as to the location of the recombination level in the lower or the upper half of the energy gap by this type of experiment. The energy levels thus obtained are at 0.17 ev from the valence band or 0.20 ev from the conduction band in p‐type silicon and at 0.22 ev from the valence band or 0.25 ev from the conduction band in n‐type silicon. View full abstract»

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  • Effect of Heat Treatment upon the Electrical Properties of Silicon Crystals

    Page(s): 1427 - 1436
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    Studies have been made of the process in which donors are introduced into silicon by heating in the temperature range 300°–500°C and are caused to disappear on heating at higher temperature. This phenomena is shown to depend on the conditions of growth and the heat‐treatment history of the crystal. Evidence is summarized which shows that oxygen is the impurity from which the donors are formed. The characteristics of the processes involved are described and possible mechanisms are discussed. View full abstract»

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  • Explosive Induced Shock Waves. Part I. Plane Shock Waves

    Page(s): 1437 - 1441
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    The explosive production of plane shock waves in solids is analyzed in the approximation that third and higher order terms in the shock strength can be neglected, and a procedure is developed for calculating the attenutation of the shocks. Application is made to the problem of determining the equation of state of the burned explosive gas. View full abstract»

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  • Junction of Smooth Flared Wave Guides

    Page(s): 1441 - 1448
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    Stevenson's general theory of electromagnetic horns or flared wave guides, which is valid only for geometrical configurations whose cross sections are continuous along the direction of propagation together with their first and second derivatives, is generalized to include sudden jumps in the first derivatives of the cross sections. Thus the junction of wave guides with different flares and of arbitrary cross sections can be treated, provided that at the junction plane the cross sections on the two sides are identical. General expressions are derived for the reflection and transmission coefficients correct up to the second order in flare angle. Explicit results for a few configurations of practical interests are derived, including some second‐order ones. In cases where special theories exist, comparisons are made with favorable results. In addition, an experimental check is performed. View full abstract»

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  • Growth and Defect Structure of Sapphire Microcrystals

    Page(s): 1449 - 1454
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    Examination of small euhedral crystals of α‐Al2O3 (sapphire) that were observed following oxidation of aluminum and an aluminum alloy in wet hydrogen at high temperatures showed that growth probably occurs by decomposition of AlO on an Al2O3 surface. Rapid growth occurs on the tips of needles and the edges of platelets at lattice steps formed by intersection of hollow screw dislocations with these surfaces. Screw dislocations were detected by x‐ray measurement of the lattice twist they produce in the needle‐like crystals or ``whiskers.'' Needles were bent to elastic strains of over 2% corresponding to a strength of 1011 dyne cm-2. View full abstract»

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  • Some New Aspects of the Reflection of Electromagnetic Waves on a Rough Surface

    Page(s): 1455 - 1463
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    The reflection of a plane‐electromagnetic wave from a rough perfect conductor is investigated. The roughness is represented by hemispherical bosses whose radii and mutual distances are small relative to the wavelength. This problem is solved taking into account the electromagnetic interaction of the bosses. Aside from throwing some light on the limitations of approximate methods, the present solution reveals some effects not known before. For grazing incidence and vertical polarization the interaction has a drastic influence in that it causes a complete phase reversal of the reflected wave, near a 45 degree incidence the influence of the roughness vanishes. These effects do not occur for horizontal polarization. An approximate treatment for the case of the imperfect conductor is indicated. The analogous case for the acoustic wave is also developed and shows similar behavior. The effect of the roughness is shown to be equivalent to a boundary condition for the wave equation. Extension of the method to a more general type of roughness, and to the case of statistical and asymmetric shapes and distributions, is briefly discussed. View full abstract»

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  • Emissivities of Metallic Surfaces at 76°K

    Page(s): 1464 - 1467
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    Heat transport by radiation between surfaces at 300°K and 76°K was measured to evaluate the effective emissivities of a number of technical grade or commercially available metals with unknown metallurgical history. The surface with the lowest total hemispherical emissivity was an unbuffed silver‐plated surface. It was found that the emissivity of surfaces was lowest when used without any mechanical working and that the ability to absorb radiant energy varied with the length of time the surface was kept cold, even at a pressure less than 10-6 mm Hg, indicating surface contamination by residual gases. View full abstract»

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  • On the Mechanism of Operation of the Barium Aluminate Impregnated Cathode

    Page(s): 1468 - 1473
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    Emission and evaporation characteristics of a porous tungsten cathode impregnated with the composition 5BaO·2Al2O3 are presented and are interpreted in terms of the cathode mechanism. Barium necessary for activation is generated by the reaction,

     2 
     3 
    Ba3Al2O6+
     1 
     3 
    W=
     1 
     3 
    BaWO4+
     2 
     3 
    BaAl2O4+Ba
    , and is transported through partially clogged pores, the length of which increases with time, predominantly via Knudsen flow. During transport, oxygen is acquired from the tungsten, leading to a substantial content of BaO in the evaporant. The BaAl2O4 component of the impregnant is inert. Emission is substantially lower than that of an L cathode, presumably because of release of a poisoning agent accompanying the activator. View full abstract»

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  • Drift Mobility Measurements

    Page(s): 1473 - 1478
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    Measurements of drift mobility have been made by observing the transit time t of a pulse of charge carriers over the distance x between the point of photoinjection and a ``point of detection.'' The detector point may be a reverse biased junction, a constriction in the cross‐sectional area, a point contact electrode, or other electrically indicating semiconductor construction. The arrival of the injected pulse at the detector results in a relatively large change in the conductance of the specimen. A signal taken from a load resistor in series with the sample is observed on the CRO. The time t is plotted against x. The reciprocal slope of the curve gives pulse drift velocity which when divided by the field strength E(x) gives the corresponding mobility μ(x). For a junction, electron mobility is determined by injection in the p region; hole mobility is determined by injection in the n region. View full abstract»

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  • Fields in Gap‐Excited Rectangular Ducts

    Page(s): 1479 - 1483
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    The electromagnetic field in a rectangular wave guide, cut in two by a plane perpendicular to its longitudinal axis, is investigated. A voltage applied across the two halves of the guide generates the field structure, which is analyzed for several values of the frequency (between zero and cutoff) and of the aspect ratio of the cross section. The problem is of interest for the design of particle accelerators. View full abstract»

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  • Theory of Peeling through a Hookean Solid

    Page(s): 1484 - 1485
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    When the adhesive is a Hookean solid and the adhesive joint between a rigid plate and a flexible ribbon is peeled, the force required for peeling is 0.3799 wσ(E/E1)14δ34y014, if w denotes the width of the ribbon, σ the tensile strength of the adhesive, E and E1 the moduli of elasticity of the ribbon and the adhesive, respectively, δ the thickness of the ribbon, and y0 the initial thickness of the adhesive film. If δ=y0, the ratio of tensile force to stripping force needed for separation is of the order of l/y0, l being the length of the ribbon. View full abstract»

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  • Analysis of the dc and Pulsed Thermionic Emission from BaO

    Page(s): 1486 - 1492
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    The effects of field penetration and donor mobility on the chemical potential of BaO have been computed by using a nondegenerate single donor level semiconductor model. Calculations which neglect the effects of surface states and porosity predict that the pulsed emission starts lower, but increases with field more rapidly than given by simple Schottky theory, actually being capable of exceeding the theoretical Schottky emission. The dc emission level is always lower than the pulsed emission, the difference being more pronounced at higher fields and for less active cathodes. View full abstract»

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  • Measurements of the Effective Resonance Integral in Uranium Metal and Oxide in Different Geometries

    Page(s): 1493 - 1502
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    A series of measurements of the effective resonance integral in uranium metal and oxide, UO2, has been made. Measurements were performed on simple rods, on a few tubes, empty or filled with a moderator, and on clusters of rods. Formulas for the effective resonance integral as a function of S/M and (S/M)½ are given for metal and UO2. In addition the variation of the resonance absorption of neutrons as a function of depth in metal rods has been studied. The results are given in the form of curves. View full abstract»

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  • Calculation of Energy Dissipation by Gamma Radiation near the Interface between Two Media

    Page(s): 1502 - 1508
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    A Monte Carlo calculation was made of the energy dissipation by gamma radiation in a medium with the scattering properties of water which consists of two semi‐infinite regions, one of which is much denser than the other. The calculations are for a 1.28‐Mev point‐isotropic source at or near the boundary plane separating the two regions. The results are presented in terms of boundary correction factors which express the change of energy dissipation compared to that prevailing at the same location in a medium of uniform density. The analysis of the results leads to the conclusion that the boundary effect is rather insensitive to the atomic number of the medium, and is mainly a function of the density change. The Monte Carlo results are in good agreement with an experiment of Soole on the propagation of radiation in the air above the ground, and an experiment by Titus on the dose distribution in iron. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Meet Our Editors

Editor
P. James Viccaro
Argonne National Laboratory