Volume 30, Issue 6, 01 June 1959
Index of content:
30(1959); http://dx.doi.org/10.1063/1.1735243View Description Hide Description
Fast moving plasmas encountering transverse magnetic fields of order 104 gauss are decelerated so rapidly as to produce reflected shock waves. Observations in hydrogen at gas pressures of 1 to about 10 mm Hg are analyzed. There are critical conditions of magnetic field for the onset of the reflection. The velocities of the advancing and reflected waves are recorded as a function of pressure and field.
Experimental Verification of Theoretical Relations between Total Gas Absorptivities and Total Gas Emissivities for CO30(1959); http://dx.doi.org/10.1063/1.1735244View Description Hide Description
An experimental study has been carried out for the purpose of verifying theoretical predictions concerning the relations between total absorptivities and total emissivities for transparent gases. The experimental conditions have been designed in such a way as to permit a direct check of theoretical relations derived for (a) nonoverlapping dispersion lines and (b) spectral lines with sufficient pressure broadening to permit neglect of the rotational fine structure. A comparison between the emissivities derived from absorptivity measurements and emissivities calculated from the spectroscopic constants of CO shows a good agreement (within 20% for most of the temperature range).
The apparatus for the measurement of total gas absorptivities is described. Results for total absorptivities of carbon monoxide measured at temperatures between 300 and 500°K are given and total emissivities have been calculated in the temperature range of 300 to 1600°K. The range of total gas pressure is 0 to 515 psia.
30(1959); http://dx.doi.org/10.1063/1.1735245View Description Hide Description
Dynamic pyroelectric techniques have been used to study single crystal BaTiO3hysteresis loops which have been reported in several recent investigations to be asymmetric with respect to both the polarization and electric field axes. It is shown that an apparent polarization bias occurs because of electrode‐edge effects and that this bias may be shifted with an appropriate application of a dc field which serves to alter the direction of the polarization in fringe regions which contribute to the observed pyroelectric signal. The pyroelectrichysteresis loops are symmetric with respect to the polarization when electrode‐edge effects are eliminated. These data strongly suggest that asymmetric remanent polarizations reported in several piezoelectric and pyroelectric investigations may have been due to edge effects. The pyroelectrichysteresis loops are found to be biased with respect to the electric field axis in the same manner as that reported in a recent piezoelectric study. Small residual pyroelectric signals observed at temperatures above the Curie point of the bulk material do not result from fringe effects, and the earlier interpretation of the residual signals in terms of a polarized surface layer is consistent with the present results.
30(1959); http://dx.doi.org/10.1063/1.1735246View Description Hide Description
Interdiffusion in a nondegenerate, exhaustion range, binary ionic semiconductor is investigated using the recently improved theory for the concentrations of defects in crystals and Wagner's phenomenological flow equation. The composition dependence of the interdiffusion constant is found to be determined by the ratio of the ion jump frequencies, the Schottky constant, and the intrinsic concentration of conduction bandelectrons. The removal of the restriction to an exhaustion range semiconductor and the replacement of the basic assumption of local electroneutrality are discussed.
Single Crystal Anisotropy and Magnetostriction Constants of Several Ferromagnetic Materials Including Alloys of NiFe, SiFe, AlFe, CoNi, and CoFe30(1959); http://dx.doi.org/10.1063/1.1735247View Description Hide Description
The anisotropy and magnetostriction of single crystals of several ferromagnetic materials have been determined experimentally. The materials include the metals iron and nickel, binary alloys of nickeliron,siliconiron,aluminumiron,cobaltnickel, and cobaltiron, ternary alloys of molybdenumnickeliron,nickelcobaltiron, and molybdenumaluminumiron, and magnetite. The effect of the order‐disorder reaction on these properties was measured for several of the alloys.
The present data for the nickeliron and siliconiron systems agree well with recently published values. Ordering generally raises the magnetostriction and lowers the anisotropy of the aluminumiron alloys near the Fe3Al composition. The first anisotropy constant, K 1, for the cobaltnickel system as derived from torque curves is similar to old data derived from magnetization curves. However, K 1 for cobaltiron (30, 35, and 45% cobalt) appears to be considerably larger than previously reported. In general, the addition of cobalt to nickel and to iron changes the magnetostriction constants (λ100 and λ111) toward large positive values. Thus, λ100 increases to 100×10−6 for 50% cobaltnickel and to 130×10−6 for 45% cobaltiron; λ111 increases to 30×10−6 for 45% cobaltiron but remains approximately constant for the cobaltnickel alloys.
30(1959); http://dx.doi.org/10.1063/1.1735248View Description Hide Description
An ultrasonicinterferometer technique for measuring the temperature dependence of the relative change in elastic constants is described in detail. Results are reported for measurements carried out as a function of frequency from 10 mc/sec to 170 mc/sec, for compressional wave propagation along the  axis of silicon over a temperature range of −60° to +15°C.
The mean value of (1/c 11)(dc 11/dT) obtained is 55.59±0.81×10−6 (°C)−1, and no frequency dependence of (1/c 11)(dc 11/dT) was found.
30(1959); http://dx.doi.org/10.1063/1.1735249View Description Hide Description
A theory of convergent, high‐efficiency electron guns for the production of dense hollow beams is presented. An approximate solution to Poisson's equation is obtained in a cylindrical coordinate system modified to account for the toroidal geometry. Experimental measurements on a series of toroidal guns tend to confirm the space‐charge theory. They also show that the annular slit in the anode very seriously affects the uniformity of cathode emission and diverges the beam more than can be accounted for by present theories. These effects of the slit appear to confine the usefulness of these guns to high‐power applications.
30(1959); http://dx.doi.org/10.1063/1.1735250View Description Hide Description
The density and distribution of dislocations in tip grownironwhiskers produced by the hydrogen reduction of liquidiron halide salts has been measured by means of x‐ray rocking curves. The data show that the more perfect whiskers have dislocation densities below 106dislocation lines per cm2. Thus, many of these whiskers which are less than 10 μ in diameter would contain, at most, only a small number of dislocations and should behave as perfect crystals. No evidence of a large elastic twist was found in any of the whiskers as would be expected for a whiskergrown by a screw dislocation mechanism. This did not completely prove that ironwhiskers must grow, therefore, by a mechanism based on coherent two‐dimensional nucleation as there are combinations of specific types of screw dislocations which will not produce elastic twists in the whiskers.
30(1959); http://dx.doi.org/10.1063/1.1735251View Description Hide Description
Experimental investigation of the flow rates of normal paraffins in porous Vycor glass shows that there are deviations from the viscosity dependence required by Poiseuille's law. A discussion of the application of capillary models to describe flow in porous media in terms of the measured porosity and surface‐to‐volume ratio points out that such models are not generally applicable, though they give useful results for some purposes. An estimate of the permeability predicted by Poiseuille's law is made by an empirical method which uses gas flow measurements in the Knudsen flow region. The equations of slip flow as derived for gases do not explain the experimental deviations from Poiseuille flow. The concept of a slipping adsorbed layer of molecular thickness at the wall of a capillary is combined with the usual Poiseuille treatment for the interior to give a result which is compatible with experiment.
30(1959); http://dx.doi.org/10.1063/1.1735252View Description Hide Description
The orientations of individual grains in cold‐rolled and annealed silicon‐iron strip are obtained for a single‐component texture and a multiple‐component texture to determine (1) the preferred orientations in the two textures and (2) some information on the nature of formation of the textures. A set of three axis density figures and a (100) pole density figure are synthesized for the multicomponent texture. It is concluded from the figures that the axis density figures give more information about the components present in the texture than a (100) pole figure does. It is also concluded that oriented nucleation is important in the development of the textures.
30(1959); http://dx.doi.org/10.1063/1.1735253View Description Hide Description
A method of making an ohmic contact to a semiconductor that does not inject minority carriers at high current densities has been found. This surmounts difficulties and limitations of previously reported experiments. Utilizing this technique, the high field current‐voltage characteristic of p‐type germanium was measured at several temperatures from room temperature to liquid heliumtemperatures, a wider range than previously reported. From these data, one can compute the drift velocity (and drift mobility) as a function of electric field and also estimate the amount of heating that will occur when a square pulse of current is passed through a p‐type germanium sample immersed in liquid helium.
30(1959); http://dx.doi.org/10.1063/1.1735254View Description Hide Description
Since the initial work of Brillouin, interest in long, dense electrom beams with a uniform velocity profile has increased steadily. Notable contributions have been made by Samuel and Harris. In this paper, the general member of this class of beams is derived. Various special cases become the equilibrium systems of current interest. In addition to these known systems, the analysis leads to new possibilities. One of these is of particular interest in that it is the first of this group of beams in which the axial velocity is important to the balance of forces on the electrons. The new beam has properties ideal for M‐type interaction and should be of considerable future importance.
30(1959); http://dx.doi.org/10.1063/1.1735255View Description Hide Description
Since the small‐angle x‐ray scattering intensity can be expressed as a Fourier integral, the techniques of asymptotic expansion of Fourier integrals can be used to calculate the small‐angle x‐ray scattering at relatively large scattering angles. Some asymptotic expansion techniques which are often useful are described. The relation between the scattered intensity at relatively large angles and the characteristic function and its derivatives is discussed. The scattered intensity for both prolate and oblate ellipsoids of revolution is calculated to provide examples of asymptotic expansion methods, and the resulting expressions are evaluated numerically. The behavior of the scattered intensity at relatively large scattering angles for platelet particles of negligible thickness is described.
30(1959); http://dx.doi.org/10.1063/1.1735256View Description Hide Description
Rotating collector measurements, made at a pressure of 10−5 mm Hg, yielded cosine distributions for all experimental conditions. Data were obtained for gas‐covered and partly gas‐covered target surfaces, for several beam incidence angles, and for ion energies of 40, 400, and 825 ev. It is postulated that the identical cosine distributions observed for both kinetic and potential ejection are caused by the existence of isotropic angular distributions for both mechanisms within the metal. A general expression is given for the angular distribution of emission from an arbitrarily shaped surface. This expression is a function of the fundamental angular distribution associated with a single element of area on that surface and the orientation distribution of the elements of area.
30(1959); http://dx.doi.org/10.1063/1.1735257View Description Hide Description
The high intensity of the anomalously transmitted x‐ray beam depends upon the coincidence of the nodal planes of the x‐ray wave field with one set of atomic planes within the crystal when the crystal is set for Laue diffraction. If there is any structuraldefect within the crystal which causes some of the atoms of the crystal to deviate from their normal location in perfect planes, these atoms will no longer be at the nodes of the x‐ray wave field and by their absorption they will reduce the transmitted intensity.
The present paper shows how this effect may be employed to measure the amount of microstrain present in nearly perfect germanium crystals. It is found that some apparently dislocation free crystals show a greater degree of crystalline imperfection than crystals with a finite dislocation count.
30(1959); http://dx.doi.org/10.1063/1.1735258View Description Hide Description
We have measured the carrier density as a function of temperature in n‐type germanium which has been plastically deformed by bending, and find that it can be accounted for on the basis of Read's theory if the dislocation acceptor level lies 0.18 to 0.20 ev below the conduction band. The analysis indicates that the dislocation density introduced by plastic bending is about 8 times the theoretical equilibrium density that would correspond to zero internal stress. We observe that the mobility for current flow along the bending axis is the normal mobility, which indicates that the dislocations are parallel to the bending axis, although they may zig‐zag with line segments along (110) type directions. The mobility perpendicular to the bending axis is in qualitative agreement with the theory given by Read, although the theory tends to underestimate the reduction of mobility below 50°K. We have extended Read's theory to the case where the current flows along the bending axis and the magnetic field is perpendicular to the bending axis.
30(1959); http://dx.doi.org/10.1063/1.1735259View Description Hide Description
A study was made of crystallite orientation in cubic ferrites when pressed in a magnetic field. One easy axis orients in the field direction, the other easy axes lying at random in or near a perpendicular plane. Experimental torque curves have the theoretically predicted shape. The magnetic field required for microwaveresonance is lower than in the same nonoriented ferrite if the axis of alignment and the field are parallel. This occurs because the anisotropy field Ha is no longer randomly oriented but helps to supply part of the resonant field requirement. Values of saturation magnetization (Ms ), anisotropy energy (K), and resonant field (Hr ) at 14 775 mc/sec were measured on a series of oriented polycrystallinenickel cobalt ferrites. Values of the measuredresonant field are compared with values obtained from Kittel's resonance relation using the independently measured values of Ms and K.
30(1959); http://dx.doi.org/10.1063/1.1735260View Description Hide Description
Dynamic piezoelectric resonance measurements have been made on single crystals of bariumtitanate in the temperature range from room temperature to 160°C. In the ferroelectric region (room temperature to 120°C) the material is spontaneously polarized and hence naturally piezoelectric. For this range of temperature results are presented for the elastic compliance coefficients s 11 E and s 11 P , the combination (2s 12+s 66) at constant field and constant polarization, and the piezoelectric coefficient d 31 as functions of temperature. Above the Curie temperature (120°C) the piezoelectric resonances can be observed only by polarizing the crystal with an external field. From measurements of the resonant frequencies in crystals having their longitudinal axes along the (100) and the (110) direction, and the assumption of the validity of the Cauchy relation (c 12=c 44), the elastic coefficients at constant polarization have been determined as functions of temperature and polarization from the Curie point to 160°C. The strains induced by the polarization in a stress‐free crystal are shown to be proportional to the square of the polarization, for values of polarization up to one‐third of the spontaneous polarization at room temperature.
30(1959); http://dx.doi.org/10.1063/1.1735261View Description Hide Description
A filamentary structure has been used to compare the electrical properties of a germaniumsurface with those of an adjacent p‐n junction intersecting the same surface.Surface charge is varied by field effect plates in the isolated portion of the filament and near the junction. An orderly relation can be found between surface potential variations and changes in the reverse currents across the junction. At low bias, the junction current varies with surface recombination velocity, and for bias near breakdown, the breakdown voltage varies with induced charge at the surface. For inverted surfaces, the low bias current varies rapidly as expected from channel length variations. With inverted surfaces, channel growth leads to large reverse current variations with surface potential, but breakdown voltage becomes independent of surface charge. These variations are considered in terms of simple theory, and device implications are discussed.
30(1959); http://dx.doi.org/10.1063/1.1735262View Description Hide Description
The kinetic theory for the rate of stress‐assisted precipitation on dislocations is re‐examined in order to extend the work of Cottrell and Bilby. Two approximate expressions are used for the elastic interaction between a solute atom and edge and screw dislocations: V=−A sinθ/r and V=−B/r, respectively. The resulting partial differential diffusionequations are integrated numerically to get the time‐dependent rate of precipitation on an isolated dislocation. These results are used to calculate the short‐time part of the precipitation curve for an array of dislocations. Exact steady‐state solutions to the diffusionequations are derived for both interactions and are used with a variational procedure to establish the long‐time part of the curve for a regular array. For very short times the precipitated fraction W is proportional to t ⅔ as derived by Cottrell and Bilby, but this result is not accurate over the range of t during which most of the precipitation occurs. The long‐time part of the curve is given accurately by W=1−exp(−t/τ), where τ can be calculated by replacing each dislocation and its stress field by a cylinder with an ``effective capture radius,'' the value of which is calculated for each form of interaction. Complete precipitation curves are obtained for a regular array by combining the short‐ and long‐time results, and it is shown that these are changed but slightly if the array is random. These results differ significantly from a formula suggested by Harper to extend Cottrell and Bilby's work, and they thereby indicate that the interpretation of the precipitation process for carbon in alpha‐iron is not yet entirely established.