摘要:

Pulse breakdown tests on individual specimens with self‐healing breakdowns resulted in information on both the thermal and the electric breakdown properties. Thermal breakdown due to Joule heat was found to occur nearly uniformly over the whole specimen at voltages generally lower than the electric breakdown. voltages. Calculations with relations derived for the thermal breakdown field agreed well with observations showing increase of breakdown field with decreasing pulse duration. Electric breakdown was found to be a chance event producing breakdown holes tens of microns in diameter. The process was interpreted to consist of three consecutive stages: (1) the field produces a very small charge pulse causing a temperature rise of a few hundred degrees centigrade in a breakdown channel; (2) this induces thermal runaway in the channel; and (3) the energy stored in the specimen discharges through the channel causing destruction. The magnitude of the charge pulse, duration of the process, and the size of the breakdown hole were calculated.

ISSN:0021-8979    

DOI:10.1063/1.1658070

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The theory and performance of two types of pyroelectric TGS detectors working at room temperature, one type having electrodes on the front and back surfaces of the crystal plate and the other type with electrodes on the two‐side surfaces, have been investigated. They have the same signal‐to‐noise (S/N) ratio at high frequencies, but the second type detectors, when used with a high‐bias resistor, give a higher signal if they have a long edge parallel to the pyroelectric axis. One TGS detector, modified to give a bandwidth of 100 kHz was compared to a gold‐doped germanium detector using a CO2laser as the source. The S/N ratio of the TGS detector is nearly ⅕ of the germanium detector. The type II detector has also been used to study a HCN laser pulse. The possibilities of pyroelectric detectors working at room temperature appears promising in spite of their intrinsic character of thermal detectors.

ISSN:0021-8979    

DOI:10.1063/1.1658071

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The thin‐layer lathe‐sectioning technique has been used to measure the solute diffusivities of cobalt, silver, and gold in dhcp and bcc praseodymium. The diffusivities in the bcc phase can be describedDAg=3.2×10−2exp(−21 500/RT) andDAu=3.3×10−2exp(−20 100/RT) cm2/sec. In polycrystalline samples the average of the diffusivities along the two axes of dhcp praseodymium can be expressed byDCo=4.7×10−2exp(−16 400/RT),DAg=1.4×10−1exp(−25 400/RT), andDAu=4.3×10−2exp(−19 700/RT) cm2/sec. These diffusivities are substantially higher than the self‐diffusion coefficients of praseodymium. The change in the crystalline structure of the matrix affects only slightly the solute diffusivities, contrary to its effect on the self‐diffusion coefficients. The remarkable similarity of these results with those concerning the solute diffusion of noble metals in Group III‐B and IV‐B metals, suggests that the same diffusion mechanism by interstitials operates in both cases.

ISSN:0021-8979    

DOI:10.1063/1.1658072

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Self‐diffusion in InSb was studied, using radiotracers and refined sectioning techniques. The diffusion coefficients of neither In nor Sb seemed to depend on the ambient Sb pressure. A few pits several microns in depth were found to develop during diffusion of both In and Sb in InSb. Radioactivity associated with these pits led to tails in the diffusion profiles. The In:Sb divacancy is proposed as the defect primarily responsible for self‐diffusion of both components in InSb. The activation energy for diffusion for both In and Sb was found to be 4.3 eV. This consisted of effective enthalpies of formation and motion for the divacancy of 3.2 eV and 1.1 eV, respectively. The enthalpy of formation of the single vacancies was estimated to be 1.76 eV. The pre‐exponentialsD0in the Arrhenius relation for diffusion of In and Sb were 1.76×1013and 3.1×1013cm2sec−1, respectively. These high values are attributed primarily to the large vibrational entropy contributions of a divacancy.

ISSN:0021-8979    

DOI:10.1063/1.1658073

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Electromagnetic wave propagation through materials that possess both Faraday rotation and birefringence is analyzed. A matrix equation is developed which relates the amplitude and relative phase of the electric vectors between any two points along the propagation direction. It is shown that the presence of birefringence can drastically affect the behavior of wave propagation and that it is considerably different from pure Faraday rotation. Methods of measuring the material parameters are also described. Criteria for viewing domains in this type of material are established. It is shown that the thickness of the sample plays a great role in determining the contrast between domains and at some thicknesses no contrast at all can be obtained. It is also shown that the method using elliptical analyzers gives greater contrast over the plane analyzers. Photographs of domain patterns in a wedge of ytterbium orthoferrite are presented and they verify the calculated results.

ISSN:0021-8979    

DOI:10.1063/1.1658074

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The interaction between conduction electrons with energies from 0.25 to 7.5 eV and longitudinal optical phonons in alkali halides is studied in detail by time‐dependent perturbation theory. Expressions for the rate and angular distribution of scattering are obtained. The electron‐transport problem is then solved with the exact quantum mechanical scattering results by a direct simulation Monte Carlo method. Probabilities of escape and average energy losses for electrons generated isotropically at a certain depth in the material, with a given initial energy, are computed for CsI, KCl, NaF, and LiF. A simple theory shows the effective mass and temperature dependence. The effect of including scattering to angles other than forward is quite apparent in the results.

ISSN:0021-8979    

DOI:10.1063/1.1658075

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The phenomenon of secondary emission from alkali halides is studied in transmission. This allows the variation of one more parameter (thickness) than in conventional reflection studies. An empirical method based on published results of scattering by thin foils is used to determine the spatial dependence of the internal electron excitation function. The results of the Monte Carlo calculations presented in the previous paper (Part I) are used to generate a mathematical model of secondary emission. Measurements of pulsed secondary yield and of energy distribution of secondary electrons from uncharged films of CsI, KCl, NaF, and LiF are carried out at various film thicknesses and primary energies. By matching one single experimental point to the mathematical model, complete theoretical curves of yield for each material are generated. The results show that the spatial dependence of the excitation function taken together with the secondary escape results of Part I are sufficient to account for the variations of yield of different materials as a function of thickness and primary energy. An absorption attributed tod‐like conduction bands is experimentally observed in KCl. The energy dependence of the internal excitation function is obtained and it is also shown that it is incorrect to characterize the probability of escape of all internal secondaries by a single exponential. The implications and shortcomings of the experiments are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1658076

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

In impulse gaseous breakdown, it has never been quite established how the transition from the low ion density of the primary streamers to the high carrier density of the pre‐spark channel occurs. This phase of development was investigated for air and N2by employing the Lichtenberg figure technique. Gas pressure varied between 50 and 760 Torr. It was surprising to detect an ionization process, termed a ``secondary leader,'' that is distinctly different from the primary streamer. During this process a relatively highly ionized channel is formed. Similar channels were previously observed only under static voltages and in very long gaps. The paths of the secondary channels were found to be narrow and to follow a radial pattern; they terminate in ``threads'' of low intensity that have an irregular circular pattern. Measurements were made of their onset voltage and their rate of growth as a function of the voltage and pressure. Their onset voltage in air lies between 4 and 12 kV for 100 and 400 Torr, respectively; in N2it is about 15% lower. Their length is linearly dependent upon the voltage, though the rate of growth varies with pressure.

ISSN:0021-8979    

DOI:10.1063/1.1658077

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The melting curves of silver chloride, bromide, and iodide are determined up to 68 kbar. The present silver chloride and bromide melting curves are higher by 5°–20°C than those of Deaton. The triple point of silver iodide (I)‐silver iodide (III) is at 19.1±0.5 kbar and 678°±1°C whereas Deaton reported the triple point at 22 kbar and 680°C. The volume compression versus the melting‐temperature plots are linear at low compression and begin to curve towards &Dgr;V/V0axis at higher pressures.

ISSN:0021-8979    

DOI:10.1063/1.1658078

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The quantum‐mechanical method of distorted waves for calculating the rotational relaxation rates in H2as developed by Brout is used here to calculate the relaxation time for the &Dgr;J=±2 rotational transitions of linear polyatomic CO2by taking into account the higher partial wave contributions. The intermolecular potential used consists of a spherical part and a nonspherical part with a constant parameter to characterize the deviation of the potential from spherical symmetry. The results obtained indicate that the collision numberZ(and hence the relaxation time &tgr;) is a monotonically decreasing function of the temperatureTfor a givenJand is a monotonically increasing function ofJfor a givenT. Except for small values ofJ, Zand &tgr; for a givenTare both approximately proportional to exp(aJ), whereais a constant. Detailed numerical results are also obtained and compared with known experimental results. It is shown that the method used here is not valid when the temperature is too high or wheneverZbecomes too close to 1.

ISSN:0021-8979    

DOI:10.1063/1.1658079

出版商:AIP    

年代:1969

数据来源: AIP