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1 Feb 1957

Volume 28, Issue 2, pp. 143-281

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Study of Boiling in Short Narrow Channels and Its Application to Design of Magnets Cooled by Liquid H2 and N2

S. G. Sydoriak and T. R. Roberts

J. Appl. Phys. 28, 143 (1957); http://dx.doi.org/10.1063/1.1722696 (6 pages) | Cited 10 times

Online Publication Date: 17 May 2004

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A study has been made of the critical heat input, Qc, to liquid H2 and N2 boiling in an annular gap, of cross‐section area, A, between a vertical cylindrical heater of height, Z, and various concentric plugs. The data are in approximate agreement with calculations based on an assumption of homogeneous and frictionless two phase flow. The pressure drop across the channel is spent primarily to accelerate the vapor being formed and the liquid carried with it. The derived relation does not contain any empirical coefficients or exponents. For ρv,2≪ρL the general equation reduces to
math
,where L is the latent heat of vaporization, ρv,2 the exit vapor density, ρL the liquid density, g the gravitational acceleration, Ze the hydrostatic head equivalent to the pressure drop across the heater, and f2 the mass fraction of vapor in the fluid leaving the heater.
Forced flow experiments give f2. At Qc equal to that found in natural convection boiling, f2=0.5 for both liquids. For Z=3 or 6 in. and a channel thickness of 0.022 in. the ratio of observed to calculated Q is 0.95 for N2 and 0.70 for H2. The calculation is equally good for critical natural convection experiments, Ze=Z, and for subcritical as well as critical forced flow measurements, which extend up to Ze=70 Z.
The optimum operating vapor pressure is discussed for magnets cooled by ideal natural convection boiling. A simple roll‐type of coil is discussed and is shown to be superior in some respects to more conventional windings.

Special Theory of Ultrasonic Machining

George E. Miller

J. Appl. Phys. 28, 149 (1957); http://dx.doi.org/10.1063/1.1722698 (8 pages) | Cited 12 times

Online Publication Date: 17 May 2004

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A model is proposed for the mechanism of material removal in ultrasonic machining. From this model and fundamental physical principles, a machining rate equation is derived for the special case where solid, circular tools are used in conjunction with a puddled slurry. A comparison of the predictions of the theory with the experimental data shows that the theory gives the correct relationship between the machining rate and the variables involved in the machining process. Suggestions for the improvement of the ultrasonic machining process are presented, and the method to be used in generalizing the theory is outlined. The poor reproducibility of the machining rate measurements is explained on the basis of the machining rate equation.

Studies on the Mechanism of Operation of the L Cathode. I

E. S. Rittner, R. H. Ahlert, and W. C. Rutledge

J. Appl. Phys. 28, 156 (1957); http://dx.doi.org/10.1063/1.1722699 (11 pages) | Cited 25 times

Online Publication Date: 17 May 2004

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Performance characteristics of the L cathode, including emission, evaporation rate, and evaporant composition, are presented, followed by an investigation of the constitution of the emitting surface. Activation of the external tungsten surface is effected by the migration thereover of strongly adsorbed BaO issuing from the pores. The active surface, which is continuously renewed during life, comprises a nearly complete oxygen monolayer on tungsten covered in turn by a complete barium monolayer. The oxygen in the dipole layer enhances emission and drastically increases the sticking time of barium. The cathode emission is close to the maximum that can be expected from a barium activated tungsten dispenser cathode.

Studies on the Mechanism of Operation of the L Cathode. II

W. C. Rutledge and E. S. Rittner

J. Appl. Phys. 28, 167 (1957); http://dx.doi.org/10.1063/1.1722700 (7 pages) | Cited 16 times

Online Publication Date: 17 May 2004

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An experimental study of the L cathode is presented, including the chemistry of carbonate decomposition and barium generation, the origin of BaO in the evaporant, the barium transport mechanism through the porous plug, and the factors determining cathode life. Carbonate decomposition is accompanied in low porosity cathodes by the deleterious reaction
math
.Barium is generated in the cavity at an equilibrium pressure by the reaction
math
and is transported continuously through the porous tungsten predominantly by Knudsen flow. During transport the barium acquires oxygen from the tungsten, producing in the evaporant a large BaO content which helps to activate the surface. Termination of life coincides with completion of the BaO☒W reaction and onset of the subsequent reaction
math
,which is accompanied by release of a poisoning agent. Material decrease in evaporation rate and a corresponding increase in cathode life may be gained by addition of SrCO3.

Work‐Function Studies of Germanium Crystals Cleaned by Ion Bombardment

J. A. Dillon and H. E. Farnsworth

J. Appl. Phys. 28, 174 (1957); http://dx.doi.org/10.1063/1.1722701 (11 pages) | Cited 54 times

Online Publication Date: 17 May 2004

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The work functions of germanium single crystals have been obtained by measuring the contact potential differences between the germanium crystals and a gold reference whose work function was measured by the Fowler method. Work function values for the bombardment‐cleaned surfaces of three samples having comparable resistivities were the same within experimental error (4.78±0.015 ev). Variation in the doping concentration resulted in work‐function changes smaller than those predicted by a simple Fermi level shift. Adsorption of oxygen at pressures of about 1×10−7 mm Hg resulted in work‐function increases of about 0.20 ev. The clean surface work‐function values could be restored after O2 adsorption by heating at 500°C for 15 min. For those cases in which changes were noted, adsorption of hydrogen and nitrogen at higher pressures (10−3 mm Hg) resulted in decreases of work function, while CO adsorption increased the work function. Measurements of the effects of strong electric fields and intense illumination on the work function suggested that these effects were associated with rather thick surface layers which could be removed by vacuum heating or ion‐bombardment cleaning. The photoelectric‐threshold level was near or slightly above the Fermi level for the ion‐bombardment cleaned surfaces. After oxygen adsorption the threshold level was below the Fermi level.

Angular Averages in the Scattering of Slow Neutrons by Gases

Howard C. Volkin

J. Appl. Phys. 28, 184 (1957); http://dx.doi.org/10.1063/1.1722702 (6 pages)

Online Publication Date: 17 May 2004

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A procedure is developed for averaging over the thermal translational motion of a gas scatterer in order to obtain observed angular averages from a knowledge of the differential cross section in the center‐of‐mass system. The results are applied to the simple case of spherically symmetrical elastic scattering with constant cross section.

Dependence of the Ferromagnetic Resonance Line Width on the Shape of the Specimen

A. D. Berk

J. Appl. Phys. 28, 190 (1957); http://dx.doi.org/10.1063/1.1722703 (3 pages) | Cited 12 times

Online Publication Date: 17 May 2004

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The dependence of line width of the ferromagnetic resonance on the shape of the sample is examined on phenomenological grounds. If a damping term of the Bloch‐Bloembergen type is assumed in the equation of motion of the magnetization, the line width for an ellipsoidal sample is given by ΔH = [1+Ms2γ2(Nx−Ny)2/4ω2]−½2/γT2. The Landau‐Lifshitz form of damping leads to a line width which is independent of the shape of the specimen.

Dislocation Damping at High Temperatures

J. Weertman

J. Appl. Phys. 28, 193 (1957); http://dx.doi.org/10.1063/1.1722704 (4 pages) | Cited 14 times

Online Publication Date: 17 May 2004

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See Also: Erratum

Show Abstract
An unpinned dislocation damping model (based on the Mott‐Nabarro solution hardening theory) was previously used to explain internal friction at room temperature and is now extended into the high‐temperature range. With the model it is possible to explain the high‐temperature internal friction which has been observed in the kilocycle frequency range for measurements made at very low strain amplitudes. In addition, the damping due to dislocation climb is considered.

Compressional Creep of Tin Single Crystals

J. Weertman

J. Appl. Phys. 28, 196 (1957); http://dx.doi.org/10.1063/1.1722705 (2 pages) | Cited 11 times

Online Publication Date: 17 May 2004

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Compressional creep tests were run on single crystals oriented so that the direction of compression was along the c axis. Two activation energies of creep were found: approximately 24 500 cal∕mole above 120°C and 12 000 cal∕mole below this temperature.

Annealing of Cold‐Worked Copper by Electron Irradiation

C. J. Meechan

J. Appl. Phys. 28, 197 (1957); http://dx.doi.org/10.1063/1.1722706 (4 pages) | Cited 9 times

Online Publication Date: 17 May 2004

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Copper wires were cold worked at room temperature to approximately a 15% reduction in area and were then irradiated at temperatures between 100° and 150°C with 1.25‐Mev electrons. The residual resistivity was observed to decrease as a function of exposure at temperatures above 100°C. The higher the temperature at which the irradiation was performed, the greater was the rate of resistivity decrease. From these data, it is concluded that one of the primary defects produced by electron irradiation becomes mobile in the temperature range, 100°–150°C. It is suggested that interstitials and vacancies produced by the irradiation initiate a process which results in the annihilation of dislocations. From an analysis of the temperature dependence of the rate of decrease, a value for the activation energy for vacancy migration in copper has been deduced: 1.28±0.10 ev.

Linear Dissipation in Solids

C. Lomnitz

J. Appl. Phys. 28, 201 (1957); http://dx.doi.org/10.1063/1.1722707 (5 pages) | Cited 54 times

Online Publication Date: 17 May 2004

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In solid materials the properties of transient creep, internal friction and dispersion can be correlated on the basis of a linear theory, if the strains are small throughout. The theory, first given by Boltzmann, is developed in some detail. Dissipative properties of the material are shown to depend on a function of time called the ``creep function'' ϕ(t).
The general condition 1∕Q≅constant is examined. This condition is compatible with a creep function of logarithmic type. Velocity dispersion of plane or spherical waves is very small in such a medium. Graphs of 1∕Q, phase and group velocities vs frequency are given, and a quantitative relationship between creep and internal friction constants is derived. The results are substantially applicable to the problem of losses in dielectrics, by carrying out the electromechanical analogy.

Air Bubbles in Water

Leonard Liebermann

J. Appl. Phys. 28, 205 (1957); http://dx.doi.org/10.1063/1.1722708 (7 pages) | Cited 33 times

Online Publication Date: 17 May 2004

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The solubility of air bubbles is observed in a variety of experiments. Freely rising bubbles exhibit a solution rate more than twice that of bubbles which are stationary: i.e., trapped on the walls of the container. The theory of solution of stationary bubbles is given but the theory of a free bubble is difficult and has not been solved. Stationary bubble observations lead to a determination of the coefficient of diffusivity: 2.9×10−5 cm2∕sec at 27°C; the temperature dependence is considerable, obeying Einstein's equation relating diffusion and viscosity. The effect of surface contamination on diffusion is analyzed; bubble solution in the presence of contaminants is not greatly altered. Experiments are described showing that air bubbles of dimension less than 1μ lodged on hydrophobic particles are not soluble and can exist indefinitely. It is shown that hydrophobic particle residues frequently remain after bubble solution, even in relatively pure water. These residues function as bubble nuclei for boiling or for cavitation.

Maser Oscillators

J. C. Helmer

J. Appl. Phys. 28, 212 (1957); http://dx.doi.org/10.1063/1.1722709 (4 pages) | Cited 11 times

Online Publication Date: 17 May 2004

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Two maser oscillators have been constructed and operated. The behavior of one maser has been observed under various operating conditions by comparing it with the second maser which is used as a reference standard. The expeimental setup is shown and experimental results are given. The frequency‐pulling effects of the beam and the oscillation amplitude as a function of cavity‐tuning are compared with the theoretically expected behavior. It is shown that the simple behavior predicted by theory exists only for oscillation frequencies which are well removed from line center.
The theoretical curves are obtained from a new analysis which includes the velocity distribution in the beam. A comparison is made between the velocity‐distributed and uni‐velocity theories. It is shown that the introduction of the velocity distribution drops the maximum beam efficiency from 1 to 0.76 and causes a region of stability to appear in the beam frequency‐pulling function.

Reflection of Plane‐Polarized, Electromagnetic Radiation from an Echelette Diffraction Grating

William C. Meecham and C. W. Peters

J. Appl. Phys. 28, 216 (1957); http://dx.doi.org/10.1063/1.1722710 (2 pages) | Cited 7 times

Online Publication Date: 17 May 2004

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A variational method is used to calculate the distribution of energy reflected from an echelette diffraction grating. Experiments performed using a klystron generating 3.2‐cm electromagnetic waves which impinge upon a large scale grating agree with the calculations to within a few percent, the error being that expected from the variational formulation.

Ferrite Slabs in Transverse Electric Mode Wave Guide

H. Seidel

J. Appl. Phys. 28, 218 (1957); http://dx.doi.org/10.1063/1.1722711 (9 pages) | Cited 4 times

Online Publication Date: 17 May 2004

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The transversely magnetized slab operating in a parallel‐plane‐type transverse electric mode may be examined from an operational viewpoint. Characteristics of the wave‐guide mode emerge from considerations of symmetry and some results are derived that are not evident from a first‐order perturbation theory. Operators are developed associated with various transverse strata of the wave‐guide cross section corresponding to slabs of different media within the guide. The use of these operators is systematized in application to propagation problems in both rectangular and coaxial type transmission lines. Ferromagnetic resonance is explored in ferrites obeying a reactive Polder tensor‐type description and some features of resonance are discussed.

Electrostatic Considerations in BaTiO3 Domain Formation during Polarization Reversal

Rolf Landauer

J. Appl. Phys. 28, 227 (1957); http://dx.doi.org/10.1063/1.1722712 (8 pages) | Cited 161 times

Online Publication Date: 17 May 2004

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Merz's picture of spike‐shaped domains of reversed polarization emerging from an electrode is analyzed with particular attention to its electrostatic aspects, taking into account the inhomogeneous piezoelectric distortions which accompany domain formation. The depolarization energy of a domain is evaluated. The interaction energy of the applied field and the depolarization field is shown to be negligible. The charge flowing into the electrodes as a domain expands is shown to be related primarily to the reversal of spontaneous polarization, rather than to the changes of the depolarization field. Our final results are similar in form to the expression originally given by Merz. Although a detailed domain wall theory is not yet available, we have combined an existing domain wall estimate with our electrostatic expressions, and this results in an implausibly large critical nucleus. Some effects of nonlinearities in the dielectric behavior and of internal charge distributions are discussed.

Rectification Properties of Metal‐Silicon Contacts

E. C. Wurst and E. H. Borneman

J. Appl. Phys. 28, 235 (1957); http://dx.doi.org/10.1063/1.1722713 (6 pages) | Cited 10 times

Online Publication Date: 17 May 2004

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Area contacts of twenty different metals were made on n and p silicon. The contacts were applied by the use of jet plating techniques, with the exception of alkali metal contacts which were pressure contact or mercury amalgam contact. A qualitative correlation is shown to exist between the work function of the metals and the rectification of these metals on n and p silicon. I–V characteristics taken on eleven of these metal‐silicon contacts lend further support to this picture. Consideration of a quantitative work function model is made difficult due to the many errors and interpretations involved in using metal work function values.
Transistor structures were made and studied for several of the metal‐silicon contacts. From analysis of this transistor data it is found that an excess current three orders of magnitude greater than theory predicts, must be present in the diodes made from these metals. This excess current is not adequately explained by any presently known mechanism.

Grain Boundaries for Field Emission Microscopy

E. G. Brock

J. Appl. Phys. 28, 241 (1957); http://dx.doi.org/10.1063/1.1722715 (4 pages)

Online Publication Date: 17 May 2004

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Heretofore the observation of grain boundaries with the field emission microscope has been limited by the accidental and infrequent appearance of suitable specimens. A process for preparing polycrystalline tungsten samples by bending a tungsten wire, etching a tip at the bend and heating is described. Both large and small angle grain boundaries result. As many as five tungsten grains may share a cross section of less than one micron in diameter. All the parameters required to describe the geometry of the boundaries may be obtained experimentally. Detailed observations on the dislocation structure of boundaries with angles as great as 6° are potentially possible. However, the field emission intensity from the region immediately adjoining and including the grain boundary must first be increased appreciably. Possible methods for achieving improved electron emission from the grain boundary region are discussed.

Buildup of Electroluminescent Brightness

Claus H. Haake

J. Appl. Phys. 28, 245 (1957); http://dx.doi.org/10.1063/1.1722716 (6 pages) | Cited 2 times

Online Publication Date: 17 May 2004

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The buildup of electroluminescent brightness is compared to the buildup of photoluminescence under various conditions which affect the electron population in traps. A qualitative explanation is proposed as to the mechanism of buildup and conclusions are drawn which confirm the observation that electroluminescence is confined to small regions in the phosphor crystals.

Resonance Absorption of Neutrons by Uranium Cylinders

Monte V. Davis

J. Appl. Phys. 28, 250 (1957); http://dx.doi.org/10.1063/1.1722717 (5 pages) | Cited 5 times

Online Publication Date: 17 May 2004

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The integrated effective resonance neutron absorption cross section of uranium‐238 cylinders has been experimentally investigated in the Hanford Test Pile. The results of reactivity measurements were interpreted to yield the effective resonance integral as a function of the surface‐to‐mass ratio of the uranium cylinders. The experiments were extended to determine the Doppler coefficients resulting from heating the uranium in a constant neutron spectrum in the reactor. The effective resonance integral, ∫(σa0)effdE′∕E′, can be approximated as a function of the surface‐to‐mass ratio by
math
.The Doppler coefficient of resonance escape probability for the reactor is
math
,and the value assigned to the coefficient of the volume absorption of the resonance integral is
math
.

Carbon Tantalum Internal Friction Peak

R. W. Powers and Margaret V. Doyle

J. Appl. Phys. 28, 255 (1957); http://dx.doi.org/10.1063/1.1722718 (4 pages) | Cited 15 times

Online Publication Date: 17 May 2004

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The internal friction peak in tantalum arising from the diffusion of interstitial carbon has been located at 338°C for vibration frequencies of 0.55 cps. The corresponding activation energy is 39.6 kcal. The identification of this peak is made difficult by its proximity to the nitrogen peak. However, the two can be distinguished by the lesser stability of the carbon peak with respect to aging at 400°C and by a different dependence of peak height on solute concentration.

Stereo‐Micrographs of Conductivity

Ludwig Mayer

J. Appl. Phys. 28, 259 (1957); http://dx.doi.org/10.1063/1.1722719 (4 pages) | Cited 6 times

Online Publication Date: 17 May 2004

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The paper deals with the utilization of electron mirror microscopy for pictorial representation of the distribution of electrical conductivity. Previously described conductivity pictures obtained by this novel kind of electron microscopy have been of the normal two‐dimensional type; this paper reports three‐dimensional display of conductivity distributions. It discusses the concept of ``stereo‐micrographs of conductivity.'' It is shown that a three‐dimensional display of the conductivity distribution of thin films is possible by combining two electron mirror micrographs to a stereo‐pair. The two micrographs are distinguished solely by the amount of current passing through the specimen. As experimental evidence of the feasibility of three‐dimensional ``conductivity pictures'' a stereo‐micrograph of a test sample with artificially prepared areas of different conductivities is shown. Limitations and precautions to be observed are briefly discussed.

Aging Characteristics of Electroluminescent Phosphors

S. Roberts

J. Appl. Phys. 28, 262 (1957); http://dx.doi.org/10.1063/1.1722720 (4 pages) | Cited 9 times

Online Publication Date: 17 May 2004

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The brightness, B, of electroluminescent light sources is observed to decay gradually as a function of operating time, t, according to the empirical formula, B=B0∕(1+t∕tc), where B0 is the initial brightness and tc is the time to half‐brightness. At 60 cps the values of tc range in the hundreds to thousands of hours, while at 5000 cps tc is observed to be less than 100 hr for the particular phosphor used. The value of tc depends slightly, if at all, on voltage; but a very significant change in the voltage dependence of brightness occurs during the aging process. The results are interpreted on the basis of the Piper‐Williams theory and are thought to be consistent with a field‐induced migration of the deep donor impurity.

Ultrasonic Double Refraction in Single Crystals

P. C. Waterman and L. J. Teutonico

J. Appl. Phys. 28, 266 (1957); http://dx.doi.org/10.1063/1.1722721 (5 pages) | Cited 16 times

Online Publication Date: 17 May 2004

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The phenomenon of ultrasonic double refraction and methods of observing it with pulsed echo methods are described in some detail. Two causes of ultrasonic double refraction are described. Double refraction effects were observed in three germanium single crystals. The main cause of the effects reported here seems to be a small angular difference between the propagation direction and a principal axis of the crystal.

Effect of Annealing in Various Gases on the Bulk Lifetime of Germanium

Kurt Weiser

J. Appl. Phys. 28, 271 (1957); http://dx.doi.org/10.1063/1.1722722 (2 pages) | Cited 1 time

Online Publication Date: 17 May 2004

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High resistivity germanium single crystals were annealed at 500°C in various gases. For an oxygen atmosphere with a trace of water vapor present, the bulk lifetime more than doubled, then decreased to below the initial value. For dry oxygen and for nitrogen, helium, hydrogen, or argon in the presence of water vapor, the lifetime first remained constant, and then decreased. Prolonged annealing in dry helium did not affect the lifetime. The data have been interpreted in terms of a ``leaching out'' of an impurity recombination center by a water catalyzed surface oxidation, and a simultaneous formation of an oxide of germanium which diffuses into the bulk and on precipitation acts as a recombination center.
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