Index of content:
Volume 29, Issue 5, 01 May 1958
29(1958); http://dx.doi.org/10.1063/1.1723277View Description Hide Description
Dislocation etch pits can be formed on LiF by a dilute aqueous solution of FeF3. In this report the etch pit formation is described in detail, and the mechanism for pit formation is discussed. The nature of the etch pits depends on the character of the dislocation, and on the exact composition of the etchant. Edge dislocations and screw dislocations etch slightly differently; the former produce deeper pits. The etching is inhibited by some segregated impurities at dislocations, therefore aged dislocations and fresh dislocations etch much differently. Etch pit formation is probably due to the preferential nucleation of unit pits one molecule deep at a dislocation, and the movement of the monomolecular steps across the surface. The relative rates of these two processes determine the shape of the etch pits. The nucleation rate for unit pits depends upon the dislocation energy, hence upon the character of the dislocation and the impurity content as suggested by Cabrera. The nucleation rate is faster at edge dislocations, because of their higher energy. The nucleate rate is low at dislocations with segregated impurities, because the impurities lower the dislocation energy. The ferric ion is adsorbed on the surface and inhibits the motion of steps, so that steeper, more visible pits are produced as the iron content is increased.
29(1958); http://dx.doi.org/10.1063/1.1723278View Description Hide Description
Polished and etched, as well as free surfaces, of bariumtitanate were studied by the direct carbon replica technique. Domain configurations of both the 90° and 180° type were made visible at a higher magnification than has been possible by optical methods. The behavior of 90° domains at a grain boundary was studied and photographed. Hexagonal and square growth patterns of the free surface were observed and photographed.
29(1958); http://dx.doi.org/10.1063/1.1723279View Description Hide Description
The results of a numerical treatment of the dependence of half‐widths of electron energy distribution on temperature, field, and work function are presented for the electrons emitted from a metal at temperatures and fields within the extended field emission range. For the distribution, the width of the peak at half maximum and the partial widths from peak to half‐maximum on either side are presented graphically as a function of one parameter depending on temperature, field, and work function. The peak energy can also be determined in terms of this parameter.
29(1958); http://dx.doi.org/10.1063/1.1723280View Description Hide Description
It has been demonstrated that dislocations can be revealed as etch pits in copper crystals doped with a small amount of Te. The progress of polygonization of such copper after bending was followed with etch pits and x‐ray diffraction. It was found that climbing occurred at 500°C and that polygonization was complete after 2 hr at 1000°C. In similar experiments with three samples of nominally 99.999% copper, the one which was probably purest did not polygonize, while the other two did so. This indicates that if impurity is necessary for polygonization, only a very small amount is required.
29(1958); http://dx.doi.org/10.1063/1.1723281View Description Hide Description
Infrared radiation has been used to obtain a direct measure of the added carrier concentrations immediately adjacent to a junction when a current was passing through it. The currentversuscarrier densitycharacteristics thus determined can provide sensitive tests of junction theory. For junctions between two highly dopedgermanium regions and low injection levels, the experimental results agree with existing theory. For these junctions and high injection levels, or for junctions between regions where one or both sides may be lightly doped and for arbitrary levels of injection, it is necessary to extend the theory. This is done by extending the boundary conditions for higher levels of injection and using the current equations in the ambipolar form, where the field as well as the diffusioncurrents are considered. The resulting currentversuscarrier density relationship involves the total current and takes into account, for both sides of the junction, the change in conductivity with injection level and the change in the drift length with the applied electric field. If, in addition, the change in lifetime with injection level is taken into consideration, good agreement obtains between experiment and theory. Current‐voltage relationships are also derived which contain the above mentioned improvements.
29(1958); http://dx.doi.org/10.1063/1.1723282View Description Hide Description
Cleaved germanium surfaces, oxygenated at room temperature, were heated under high vacuum and the restoration of their oxygen‐adsorbing capacity was determined. No restoration was observed at 425°C. Above 575°C, however, the oxygen‐adsorbing capacity of the surfaces was completely recovered. Discharge of GeO from the surface was associated with this process. The restoration process followed first‐order reaction kinetics with an activation energy of 56 kcal/mole. Concurrently with restoration a pronounced decrease in the surface area was observed. The results are discussed in terms of the kinetic and energy requirements of the system.
29(1958); http://dx.doi.org/10.1063/1.1723283View Description Hide Description
This paper describes a 4.3‐mm radiometer and measurements made with it of the apparent temperature of various terrestrial materials, the attenuation through the atmosphere and the temperature of the sun. Materials whose apparent temperatures were measured included water, wood, metal, grass, asphalt, gravel and asbestos. Since their apparent temperatures are dependent upon their reflectivity, these data are interpreted in terms of the background reflected by the materials.
The attenuation vertically through a clear sky ranged between 1.6 and 2.3 db. The sun, of optical disk size, was found to be between 104 and 1.2×104°K on May 3 and June 17, 1957.
29(1958); http://dx.doi.org/10.1063/1.1723284View Description Hide Description
The noise temperature, band width, and gain modulation characteristics of a transmission maser are obtained as a function of iris coupling for fixed desired gain and other parameters. It is found with the help of a characteristic curve that certain of these characteristics can be optimized at the expense of others. The same functions are compared in the case of a reflection maser. The reflection maser is shown to be superior in most respects, although the same noise temperature may be attained with the transmission maser at a substantial sacrifice in band width and gain modulation. The reflection maser is also limited by the availability of good circulators, while a transmission maser can be made independent of load. A figure of merit for both types of maseramplifiers is obtained. This is Q 0 Z, where Q 0 is the unloaded cavity Q; Z is given by ; ξ is the filling factor; and χ0 is the negative rf susceptibility. When the cavity band width is much less than the susceptibility band width, an auxilliary figure of merit is Z.
29(1958); http://dx.doi.org/10.1063/1.1723285View Description Hide Description
The equivalent shunt impedance of a lightly coupled transmission cavity can be measured by inserting very small perturbing elements and using a simple bridge method to detect small shifts of transmission phase. A simple graphical procedure is developed for the interpretation of these measurements. It is shown that the procedure measures directly the shunt impedance R of the cavity, rather than the geometric quantity R/Q. Experimental results are presented for one such cavity, which show that phase information thus obtained is about 100 times as sensitive as amplitude information normally obtained from a transmission cavity.
29(1958); http://dx.doi.org/10.1063/1.1723286View Description Hide Description
Orthogonality relations are given for the ``four‐vector'' guided modes of anisotropic uniform wave guides and for the ``six‐vector'' guided modes of uniform wave guides containing unidirectional electron beams with axially independent dc velocities. In general, these orthogonality relations involve both the modes of the given wave guide and those of an appropriate ``adjoint'' wave guide. A description is given for the adjoint wave guides associated with wave guides which contain media whose characteristics are restricted only by the requirement that they be axially independent and which, if bounded, are subject to a variety of boundary conditions arising from idealizations of actual boundaries.
29(1958); http://dx.doi.org/10.1063/1.1723287View Description Hide Description
The application of preferential etching techniques to the study of crystalline imperfection in photographic emulsion grains is described. Both chemical etching and halogen evolution by print‐out exposure in the absence of gelatin form well‐defined pits in most cases. The concentration of chemical etch pits is dependent on the solvent used but is not sensitive to concentration or etch time over the range investigated. A general increase in etching on certain faces is found after intentionally straining the grains, but the effect is not sufficiently strong to establish a one‐to‐one relationship between etch pits and dislocations. In both silver bromide and silver bromoiodide grains, no evidence is found for the existence of any type of polycrystalline substructure. Experiments on pitting by print‐out exposure indicate that iodide ions provide internal hole traps or recombination centers.
29(1958); http://dx.doi.org/10.1063/1.1723288View Description Hide Description
Expressions are developed for the average power radiated by a high‐energy electron moving in a circular orbit. The instantaneous electron energy E(t) is assumed to vary with the time in accordance with . Spectral distributions are obtained corresponding to the radiation emitted over a partial or full acceleration interval. The numerical results predicted from the general relations are examined for a particular value of the peak energy Em =6.0 Bev and the orbital radius R=86.14 ft. In the case of these parameters, the continuous spectrum attains a peak at 0.36 A. Other numerical calculations, related to the case where the radiation is collected only over the low‐energy portion of the acceleration interval, indicate that it is feasible to utilize the continuum as a source for measurements in problems of interest to astrophysics and solid state spectroscopy.
29(1958); http://dx.doi.org/10.1063/1.1723290View Description Hide Description
The mechanisms for bulk viscosity are different between associated and nonassociated liquids. Here, a new mechanism for bulk viscosity is proposed from the standpoint of the hole theory of liquids and the rate process theory. This mechanism can explain the temperature and pressure dependencies of acoustic absorption for associated liquids and very viscous nonassociated liquids.
29(1958); http://dx.doi.org/10.1063/1.1723291View Description Hide Description
An x‐ray method has been worked out for the detection of screw dislocations in whiskers and has been proved satisfactory on α‐Al2O3whiskers in which the screw dislocation is identified by an axial pore and the twist independently measured by optical methods.
29(1958); http://dx.doi.org/10.1063/1.1723292View Description Hide Description
Glass breakage experiments were made which indicate two different mechanisms of fracture. The breaking process is dependent on the widths as well as the depth of the origin flaws. When the fracture is of the large, open type, the reciprocal of the breaking stress is a linear function of the depth of flaw; when the flaw is minute, the reciprocal of the breaking stress is a linear function of the square root of fracture depth.
A pronounced strength increase was observed in cuts formed under various liquids and aged for various lengths of time. This increase took place about one hour after cutting and was interpreted as a rehealing phenomenon. Cuts made in air did not show the rapid strength increase.
Cycle fatigue tests were also made on laths of glass and it was observed that there was an initial decrease in strength followed by an increase. This was interpreted as rehealing effect in the minute type of flaw.
29(1958); http://dx.doi.org/10.1063/1.1723293View Description Hide Description
Application is made of the semi‐asymptotic method of Spencer to the penetration and slowing down of neutrons in infinite media. This method can handle complete numerical input data, and is not restricted in distance. Calculations are carried out for the ideal constant cross section case, and a 1‐kev point source in air. Complete flux spectra for the 1‐kev point source are given for distances out to 100 mean free paths (mfp).
29(1958); http://dx.doi.org/10.1063/1.1723294View Description Hide Description
A simple procedure for determining the ``instantaneous'' absolute evaporation rate of barium from dispenser cathodes is presented. The method entails exposing a clean tungsten wire to a stream of barium and noting the time required to reach maximum emission. The sensitivity of the wire as a detector of total barium is established on an absolute basis by chemical calibration. It has been found that the wire sensitivity is a function of the barium oxide content of the evaporant stream. This fact may be employed to determine the oxide composition of the evaporant from wire emission‐time measurements and a single chemical analysis. It is also possible to obtain approximate, instantaneous values of total barium and the fraction BaO at any time during tube life from wire emission‐time measurements only. Calibration data are presented for almost the full range of Ba–BaO compositions.
29(1958); http://dx.doi.org/10.1063/1.1723295View Description Hide Description
Positive‐ion effects have been observed in pulsed electron beams of short duration (0.5 to 5 microseconds), under conditions of operation normally encountered in high‐power microwave tubes. Three different aspects of ion effects were studied; (1) beam focusing, (2) ion oscillations, and (3) ion trapping at scallop minima. Experimental results are given and correlated with previous work on ion effects by other authors.
29(1958); http://dx.doi.org/10.1063/1.1723296View Description Hide Description
Diffusion rates of tungsten in single crystal and polycrystallinenickel were measured at temperatures between 1100°C and 1275°C by using radioactive tungsten185 and a sectioning technique. Grain boundarydiffusion was observed by use of radioautographs. A simple vacancy mechanism accounts for nearly all of the diffusion; some refinement is required for the transport observed at greater depths.
The rate of reaction of polycrystalline 4.9% tungsten‐nickel alloy with SrO was measured by the hydrogen evolution technique at temperatures between 830°C and 1280°C. The rate indicates that the production of Sr in amounts up to 200 μg cm−2 is not limited by diffusion of tungsten in the nickel core.
29(1958); http://dx.doi.org/10.1063/1.1723297View Description Hide Description
A magnetic memory can be interrogated nondestructively by applying a perturbing field normal to the direction of remanent magnetization, and, at the same time, observing the sign of the reversible flux change. However, there may be a considerable irreversible flux change during the first few interrogations following magnetization. This irreversible component can be reduced by introducing magnetic anisotropy in a direction parallel to the direction of magnetization which is used to store binary information. The characteristics of the ideal memory is analyzed by means of domain theory. In an experimental memory a steel wire under tension was used for the memory material. A small solenoid was used to magnetize the wire locally and also to observe the flux change which was produced by an interrogative current pulsed through the wire itself. The general predictions of the theory were confirmed by experiment. Interrogation is non‐destructive and is completed in less than 1 μsec. The output is proportional to the square of the wire current, and discrimination is a matter of observing its polarity. A single bit can be written into a memory array by a coincidence of a wire current and a solenoid current. The wire current can be the same as that used for interrogation. A number of bits can be carried on one wire and interrogated simultaneously. The factors affecting the design of a memory array are discussed.