摘要:

For an understanding of the arc cathode spot mechanism, it is essential to determine the relative importance of Joule heating within the cathode and the energy input from the arc discharge. The problem of a source of uniform current density acting over a circular area on the surface of a semi‐infinite solid of conducting material is formulated and solved with the following results: (1) The Joule heat developed in the hemispherical volume directly under the cathode spot amounts to 38% of the total Joule heat developed in the electrode. This concentration of the heating leads to high average power densities in the cathode spot zone which amount, in the case of mercury, to 5×107w/cm3and 5×109w/cm3for current densities of 106and 107amp/cm2, respectively. (2) A comparison of the energy input to the cathode spot zone due to Joule heating and the energy input due to positive ion bombardment shows that for current densities of the order of 106amp/cm2, the former amounts to some 10–20% of the latter for such high‐resistivity metals as bismuth, antimony, and mercury. As the current density is increased to 107amp/cm2, the two energy sources become comparable for metals other than the low resistivity metals such as copper and silver. (3) The time required to bring typical electrode materials to the melting point with resistance heating alone is relatively short. ForJ=106amp/cm2and a spot radius of 2×10−3cm, bismuth (271°C) requires 4 &mgr;sec, antimony (631°C) 35 msec. The boiling point of mercury (357°C) is reached in 18 &mgr;sec.

ISSN:0021-8979    

DOI:10.1063/1.1736153

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Esaki diodes which show promise of usefulness into the millimeter‐wave region have been made from bothp‐ andn‐type gallium arsenide. Both diodes were alloyed junctions having point contact geometry and dimensions. The fabrication of these diodes is briefly described, and their initial performance as oscillators in mechanically simple circuits is discussed. Fundamental oscillations to 103 kMc have been obtained.

ISSN:0021-8979    

DOI:10.1063/1.1736154

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The Bi&sngbnd;Ag&sngbnd;O&sngbnd;Cs photocathode has been used for many years because of its high and reasonably uniform sensitivity throughout the visible spectrum. Chemical and physical studies are reported which were made to gain an understanding of the chemical nature and of the energy band model of the material. It was found that the Bi&sngbnd;Ag&sngbnd;O&sngbnd;Cs cathode consists of the semiconductor Cs3Bi, elementary Ag, one or more Cs oxides, and possibly some elementary Cs. The Ag, but not the Bi, can be replaced by several other metals. Energy band models were determined by using considerations which have been successful in the interpretation of the alkali antimonide photoemitters. From optical and photoelectric measurements, values for band‐gap energy and electron affinity were thus obtained for Cs3Bi as well as for the more complex materials represented by the symbols Cs3Bi(O), Cs3Bi(Ag), and Bi&sngbnd;Ag&sngbnd;O&sngbnd;Cs. A band gap of approximately 0.7 ev was found for all of these materials. It was shown that the oxygen reduces the electron affinity of Cs3Bi from 1.3 to 1.0 ev but does not greatly enhance the photoelectric yield. The addition of Ag to Cs3Bi or Cs3Bi(O) greatly increases the yield without appreciably reducing the electron affinity. A hypothesis is suggested to explain these effects.

ISSN:0021-8979    

DOI:10.1063/1.1736155

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A high‐energy exploding wire facility has been used to electrically explode thin metallic foils. Striation patterns are described for which the striation spacing appears to be dependent only on foil thickness and material. Magnetic probe measurements near the foil surface make evident the presence of shear currents in the foil which are believed to be, in part, responsible for the striation phenomena. The explanation of the striation phenomena described in this paper may aid in explaining the striated appearance of exploding wires in general.

ISSN:0021-8979    

DOI:10.1063/1.1736156

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Helium was generated in an Al‐0.1 at. % Li alloy by transmutation of the Li6atoms during neutron irradiation. During subsequent heating of the specimens, the helium appeared to precipitate in the form of small ``bubbles.'' On using a dislocation etchant it was found that (a) the regions of largest dislocation density also contained the highest cavity density, (b) in some regions each dislocation etch pit was associated with a cavity, and (c) in other regions a series of cavities appeared to delineate the track of a dislocation. It is believed that the helium precipitates along the dislocations in the form of continuous or semicontinuous cylindrical cavities.

ISSN:0021-8979    

DOI:10.1063/1.1736157

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Ion drift in a reverse‐biasedn‐pjunction has been used to measure effective drift mobilities of Li+between 20°–125°C in Si samples containing oxygen concentrations up to 1.3×1018atoms/cm3. Previous experiments have indicated that under such conditions, the Li+and oxygen will combine to form a complex of the form LiO+. The ratio of the effective drift mobility of Li+in such samples to the known drift mobility of free Li+, when measured as a function of temperature, can be used to determine the dissociation constant of LiO+. Thus, at an oxygen concentration of 1.3×1018atoms/cm, the diffusion constant at 50°C is reduced from 1.7×10−13cm2/sec to (7.6±2.2)×10−16cm2/sec by the Li+&sngbnd;O interaction. From this and measurements at other temperatures, the dissociation constant of LiO+can be calculated, yieldingC=(5.8×1015)±30% at 50°C with an activation energy of 0.42±0.03 ev, or more generally,C=(0.5–8.5)×1022exp−[(0.42±0.03)e/kT]. At high concentrations the effective drift mobility is found to be inversely proportional to the oxygen concentration, in accordance with the model. The use of this technique for the measurement of oxygen concentrations below 1017atoms/cm3is discussed, and some examples of such measurements are given.

ISSN:0021-8979    

DOI:10.1063/1.1736158

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The kinetics of a diffusion‐limited pairing reaction between oppositely charged impurity ions in a solid have been studied by observing the capture of mobile Li+ions by B−ions in Si. The kinetics were determined by measuring resistivity vs time after the method of Reiss, Fuller, and Morin [Bell System Tech J.35, 535 (1956)]; as pairing proceeds, the resistivity decreases because of the disappearance of the charged impurity scattering associated with unpaired ions. Measurements were made between 2° and 35°C. The observed kinetics are not of first order, and are best described by a model in which pairing is largely a random process with little correlation between particular Li+and B−ions. Diffusion constants of Li+calculated from the kinetics are in accord with previous ion‐drift results.

ISSN:0021-8979    

DOI:10.1063/1.1736159

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Dielectric constant (K) and loss tangent (tan &dgr;, the dissipation factor) measurements on the plastic polyvinylidene fluoride have been made over the frequency range 50 cycles to 9800 Mc at room temperature. Pronounced anomalous dispersion inKand a peak in tan &dgr; near 10 Mc were observed. Theoretical and practical applications of the data are briefly mentioned. This material has an unusually high dielectric constant and is quite lossy, especially when compared to the chemically and structurally related plastics polyethylene and polytetrafluoroethylene.

ISSN:0021-8979    

DOI:10.1063/1.1736160

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The growth of explosion has been studied both in powdered RDX, initiated by a bursting bridgewire, and in pressed RDX, initiated by passing current through a column of RDX‐graphite mixture incorporated in the charge. In the former case, a reaction wave moves out from the bridgewire at a velocity characteristic of low‐order detonation, with a transition to high‐order detonation occurring at a reproducible induction distance which depends only weakly on the stored electrical energy. Induction distances from 9.5 mm to 17.5 mm were observed, depending on geometry and loading density. Interactions of two pre‐high‐order waves were investigated, as well as the ability of such waves to cause detonation in Composition B. In contrast, growth of explosion in the pressed RDX appears to be governed, at least initially, by thermal mechanisms; delays of more than 1 msec have been observed between the discharge of the electrical energy and substantial explosion of the charge.

ISSN:0021-8979    

DOI:10.1063/1.1736161

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The measurement of the effects of heating a substance in the vicinity of a metal contact by means of an electrical current leads to the determination of various combinations of the thermoelectric parameters sufficient to determine the electrical conductivity, the thermal conductivity, and the Seebeck coefficient. If the metal contact is small, radiation causes negligible error in the determination of the thermal conductivity. One of the combinations obtained directly is the thermoelectric figure of merit. Equations are derived which relate to the heating current an observed thermoelectric voltage or change in resistance caused by a change in temperature at a small area contact. Geometric factors are found to cancel out of these equations. Quantitative relations are also presented which set limits on the effects of radiation. An experimental method is described which has been used for making such measurements, and some experimental results are reported which permit comparison to conventional measurements in accuracy. Ways in which measurements of thermal diffusivity can be combined with the other measurements are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1736162

出版商:AIP    

年代:1961

数据来源: AIP