摘要:

A method is described for simultaneously measuring the diffusion coefficient, solubility, and permeability for a given gas in a single sample of solid material. The method utilizes solutions of the diffusion equation (for both plane and cylindrical geometry) which make it easily possible to calculate the diffusion parameters from data taken either in the period of steady‐state gas flow or in the early part of the transient period. Using ultra‐high vacuum techniques, it is possible to make the measurements with extremely small amounts of gas and without errors due to leaks or contamination in the gas handling system.Values for the diffusion parameters have been determined for helium in Pyrex glass (Corning 7740), and comparisons with previous measurements are made. Directly measured values of the diffusion coefficient are given for the first time. The diffusion coefficient and permeability both exhibit a temperature dependence of the form exp (−E/kT) both having the same activation energy (6.4×103cal/mole) within the experimental error. The solubility exhibits little or no variation with temperature over the range 25°C to 300°C, and is in good agreement with the only previous measurement, carried out at 515°C.

ISSN:0021-8979    

DOI:10.1063/1.1721760

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The asymptotic expansion of wave fields in powers of 1/kfor largek, wherekis the wave number, has as its lowest‐order term what is commonly known as the geometrical optics field. The caustics of geometrical optics are those point sets on which the zero‐order terms become infinite. It is well known that caustics may exist even where the exact wave field is perfectly regular. An investigation of reflection from cylindrical walls of arbitrary cross section shows that the occurrence of caustic points means a change in character of the asymptotic expansion of the true field such that the lowest‐order term is no longer independent ofkbut actually contains a factorkraised to a positive power. There also occurs a jump in phase along a ray passing through a caustic which, as is well known, equals &pgr;/2. As an application of the general method, the geometrical optics field is worked out in detail for the case of a plane wave incident on a parabolic cylinder, and the field is obtained in its lowest order at the focus and in the neighborhood of the focus. A similar problem for a reflector consisting of a segment of a circular cylinder is also considered in detail.

ISSN:0021-8979    

DOI:10.1063/1.1721761

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

A mass spectrometer ion collector system has been devised for the investigation of secondary electron emission by impact of ions on surfaces. Results are reported for various ions incident on clean, baked (but not atomically clean) surfaces of AgMg, CuBe, and Nichrome V targets. For rare gas isotopic ions it is found that for a given energy ion the value of &ggr; varies approximately inversely with the square root of the mass.

ISSN:0021-8979    

DOI:10.1063/1.1721762

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The methods of information theory are used in the discussion of observations under a microscope. Conclusions are similar to those obtained in a previous paper and exemplify again the difficulty of measuring extremely small distances. A comparison with the discussion of uncertainty relations shows that quantum uncertainties can be very much higher than the theoretical limit, especially when material screens or shutters are not being used and the observation is made on a free particle. This correction to uncertainty relations, however, does not introduce any change in the theory of quantized fields of Bohr and Rosenfeld.

ISSN:0021-8979    

DOI:10.1063/1.1721763

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Several inorganic substances have been examined by electron microscope and selected area electron diffraction techniques. Large crystals of sodium chloride and potassium chloride break up into many smaller crystals of the same substances. Ammonium chloride evaporates, and nitron nitrate appears merely to melt. Reduction to metal was found for silver chloride, silver nitrate, lead carbonate, and cupric oxide. Only morphological changes were observed on bombardment of silver sulfate, lead oxide, lead chloride, and gold chloride. Hydrous ferric oxide and aluminum oxide were converted to crystalline forms which could not be identified by electron diffraction.

ISSN:0021-8979    

DOI:10.1063/1.1721764

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The available experimental data on the short arcs which occur on closure of electrical contacts with potential differences less than the minimum sparking potential are shown to be consistent with the hypothesis that the arcs are initiated and sustained by field emission electrons. Positive ions then carry less than 7 percent of the current at the cathode. The primary function of the ions is to supply sufficient positive space charge to maintain the high cathode field, but the action of the discrete ions near the cathode in creating a temporary pass in the potential barrier may result in the attainment of sufficient electron emission to sustain the arc at values of the cathode field somewhat lower than that required by the Fowler‐Nordheim equation for the same current density.It is shown that the supply of volatile impurities on the electrode surfaces is critical in determining the breakdown field and the minimum arc current.

ISSN:0021-8979    

DOI:10.1063/1.1721765

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

A method of shadowing samples directly within the electron microscope has been developed in this Laboratory. This method, which uses thallium chloride immersed in distilled water as the shadowing material, is much less time consuming than is the usual method that involves high‐vacuum metal evaporation; the results obtained are not of the same high quality as those of the usual method, but the time saving often justifies the method. Polystyrene Latex (batch No. 580) is introduced on the specimen screen, to provide an internal calibration standard; this standard makes it possible to measure the angle of shadowing.

ISSN:0021-8979    

DOI:10.1063/1.1721766

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

A method for the measurement of the complex conductivity of a rocket exhaust flame is described. Typical results are shown for an acid‐aniline rocket motor and a frequency of 200 mc/sec. The importance of sodium impurities is pointed out and illustrated experimentally.

ISSN:0021-8979    

DOI:10.1063/1.1721767

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

An investigation has been made of the charging of fused quartz and borosilicate glass spheres rolling on a clean nickel surface. The results indicate that the process of acquiring charge depends only upon the nature and surface condition of the materials in contact and is independent of the pressure of an atmosphere of dry N2. The total charge, however, is limited by gaseous discharge to the metal and therefore does depend upon the pressure. Such gaseous discharge has been verified by the observation of individual discharge pulses. The rate of acquiring charge and maximum charge in vacuum has been found to depend upon rolling speed, both reaching a maximum at an intermediate speed, and to decrease with increasing surface conductivity. Since both fused quartz and borosilicate glass charge negatively in contact with clean nickel, it is inferred that both have higher effective work functions than nickel. The surface conductivity of borosilicate glass has been found to be three of four orders of magnitude higher than that of quartz. Therefore, since the charging of the two materials is of the same order of magnitude, the effective work function of the glass appears to be considerably higher than that of fused quartz.

ISSN:0021-8979    

DOI:10.1063/1.1721768

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

A calculation is made which relates the physical properties of a junction diode to the troublesome spike current arising from hole storage in the germanium. This spike current results when the diode is suddenly switched from the conducting to the nonconducting state. For small germanium pellets, this current decay is exponential with a decay considerably shorter than that indicated by the hole lifetime in the material. For larger pellets the decay is a sum of exponentials giving a considerably longer decay time, still shorter, however, than the hole lifetime.

ISSN:0021-8979    

DOI:10.1063/1.1721769

出版商:AIP    

年代:1954

数据来源: AIP