摘要:

Central‐source neutron multiplication measurements have been made on small spheres of U233, U235, U238, and Pu239. Measurements were made on four sizes of spheres, varying approximately from 1 in. to 2.5 in. in diameter. In the case of U233, only one sphere, 1.245 in. in diameter, was available. The three neutron sources, mock‐fission, Po&sngbnd;Li, and Po&sngbnd;Be, were 0.4‐in. diameter spheres. They have widely different neutron spectra. Multiplications were measured with a flat‐response long counter, and with U235, U238, and Np237spiral fission chambers, under conditions such that the error introduced by room‐scattered neutrons was negligible. Results of the multiplication measurements are given. The measurements have been analyzed to obtain the leakage spectra from the spheres in terms of three velocity groups. The Np237and U238fission chambers serve as threshold detectors defining the lower energy of the second and third velocity groups, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1723425

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Apparatus was developed by which beams of cadmium and of sulfur were simultaneously directed to a common point on a temperature controlled substrate in a demountable vacuum apparatus. Cadmium sulfide crystals were obtained. The various types of crystals: spiroidals, globules, ribbons, and needles are described together with the conditions tending to produce each type. Crystal size can be increased by repeated exposure to the beams.

ISSN:0021-8979    

DOI:10.1063/1.1723426

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

It has been found that single crystals of the ferrimagnetic garnets are transparent to visible light. Thin sections (e.g., 0.005 cm thick) transmit sufficient light for microscopic examination. The transmitted light undergoes a nonreciprocal rotation similar to the Faraday effect. By virtue of this rotation many features of the domain structure are readily visible. A magnetic birefringence has also been observed which can be used to differentiate domains whose magnetization lies perpendicular to the line of sight. It is possible to study domain structure at any temperature below the Curie point. The effects of strains set up by the polishing procedure are discussed. Finally, mention is made of possible combined microwave‐optical experiments, as well as experiments aimed at understanding the switching process.

ISSN:0021-8979    

DOI:10.1063/1.1723427

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The oxygen content of liquid silicon increases proportionally to the oxygen content of the ambient helium‐oxygen mixture for oxygen partial pressurespO2°<8 mm Hg. This observation is explained by the proportionality between the oxygen partial pressurepO2° in the ambient gas and the SiO partial pressure on the surface of liquid silicon. ForpO2°>8 mm Hg the silicon melt is covered by a film of silica and asaturation value of about 2×1018oxygen atoms per cm3is observed in the crystallized sample.

ISSN:0021-8979    

DOI:10.1063/1.1723428

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The dependence of the rate of the oxidation of silicon in oxygen‐helium mixtures on gas composition at 1410°C is discussed theoretically. At low oxygen contents of the gas, no layer of solid silica is expected to occur and the rate of attack due to formation of volatile SiO is supposed to be proportional to the oxygen partial pressure in the bulk gas. Above a critical oxygen partial pressure, solid silica may be formed and the rate of attack under steady‐state conditions may drop by several powers of ten.

ISSN:0021-8979    

DOI:10.1063/1.1723429

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Data have been obtained on the pyroelectric and piezoelectric behavior of samples of a polycrystalline barium titanate ceramic in an effort to determine the possible existence of a primary pyroelectric effect. It is shown that the total pyroelectric effect is in a direction opposite to the piezoelectric contribution resulting from volumetric changes and that, as a consequence, there must exist a primary pyroelectric effect. The time constant of the samples for generation of electrical signals from heat pulses was less than 12 &mgr;sec. Practical applications of barium titanate sensors may be found in the measurement of heat radiation beams having large cross sections.

ISSN:0021-8979    

DOI:10.1063/1.1723430

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The rate of diffusion of indium in single crystals for two orientations has been measured using the radio‐active isotope In114. The diffusion coefficients in the directions parallel to theaaxis andcaxis are given by the Arrhenius relationsDa=34.1 exp(−25 800/RT) cm2sec−1andDc=12.2 exp(−25 600/RT) cm2sec−1, respectively. The anisotropy is discussed in terms of the vacancy mechanism of diffusion.

ISSN:0021-8979    

DOI:10.1063/1.1723431

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The thermoelastic dissipation due to an edge dislocation moving at an arbitrary speed is calculated analytically and numerical results presented. It is found that, at usual stress levels, this mechanism has only a minor effect in limiting dislocation speed.

ISSN:0021-8979    

DOI:10.1063/1.1723432

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

This paper presents the general equation for self‐diffusion in deforming media. Methods of analyses for determining the self‐diffusivity as a function of time for prescribed strain histories are given for special cases of linear diffusion. No unrealistic assumptions relative to the constancy of the diffusivity with time are made.

ISSN:0021-8979    

DOI:10.1063/1.1723433

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

A reanalysis of data on the thermal conductivity of certain metal oxides has shown that the deviation from aT−1law may be fitted to a law exponential inT−1. Thus the deviations may be ascribed to the flow of excitions. The contribution to the thermal conductivity from radiative transfer is shown to be too small to fit the observed deviations.

ISSN:0021-8979    

DOI:10.1063/1.1723434

出版商:AIP    

年代:1958

数据来源: AIP