摘要:

Methods of treating the Boltzmann equation for the case of a sinusoidally distributed source of fast neutrons in a material containing hydrogen are discussed and compared. The effects of the simplifying assumptions commonly employed in reactor calculations are analyzed. A technique which is particularly suitable for accurate numerical integration of the Boltzmann equation in the above case is described. Numerical results are being obtained by this method, and will be presented and compared with results obtained from other approximate methods in a subsequent paper.

ISSN:0021-8979    

DOI:10.1063/1.1722139

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The tracer diffusion of iron in 18−8 stainless steel has been measured over a wide temperature range by the surface activity decrease method, using radioactive Fe55. The results show that the lattice diffusion coefficients can be described by the equationD=0.58 exp(−67 100/RT) cm2sec−1. The effect of variations in grain size has been determined, and it has been shown that when the grain size is small, grain boundary diffusion contributes appreciably to the over‐all diffusion process, this effect decreasing with increasing temperature.

ISSN:0021-8979    

DOI:10.1063/1.1722140

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

These papers, designated I and II, discuss measurements of excess Ba (and/or Sr) in practical oxide coated cathodes. More than 300 cathodes of various designs were prepared, aged for periods up to 50 000 hours, tested thermionically, and then analyzed chemically.Despite its great importance, the accurate measurement of excess Ba in practical cathodes is a problem whose complexity has not been adequately realized. Although the methods of the present experiments avoided many difficulties, limitations still exist. The difficulties and limitations, as well as the capabilities, can best be discussed in terms of typical measurements; we emphasize this aspect in I.

ISSN:0021-8979    

DOI:10.1063/1.1722141

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Using methods given in paper I, emission and Ba content are given on (a) 125 coated cathodes, (b) 15 coated filaments; H2evolution by 19 uncoated cathodes was also measured. For analysis, each was isolated from the remainder of its tube. Coatings varied in composition from pure SrO to pure BaO and in density from 1 to 5 mg per cm2. Ba was also measured in cathode coatings removed from their support metal. Essentially all cathodes contained excess Ba, but no cathode structure gave any correlation between Ba content and emission.These experiments contribute the following toward understanding practical oxide cathodes: If excess Ba (or Sr) is important, the significant amounts are probably less than one atom of Ba in 106molecules of (BaSr)O. Because essentially all cathodes, including some with extremely low emission, contained at least this amount, we believe that performance is seldom limited by excess Ba. The concentration of Ba (or Sr) was not affected by using pure BaO or SrO coatings or Pt supports, although each of these steps led to very low emission; the highest emissions were obtained by operating at relatively low temperature during life, but this retained no more Ba in the coat. These major effects require interpretation.

ISSN:0021-8979    

DOI:10.1063/1.1722142

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A quantitative discussion of the forward characteristic is given for point contact rectifiers. It shows that the theoretical value ofdlnI/dVin the exponential region is nearlyq/kT, and that the experimental slopes which are a fraction of this value cannot be the result of the spreading voltage. Recombination of injected carriers has little effect except at large currents beyond the exponential region. Relations are derived for the limit of very large currents, which show that &ggr; approaches a value smaller than (1+b)−1, the hole concentration at the contact approaches a maximum value proportional to the equilibrium concentration of holes at the surface, and the spreading voltage becomes a linear function of the current.

ISSN:0021-8979    

DOI:10.1063/1.1722143

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The point‐source, spherical shock wave moving into a constant density &ggr;‐law gas is considered in the limit of infinite shock strength from the point of view of the Richtmyer‐von Neumann viscosity technique. A similarity solution of this problem is shown to exist and is obtained for various boundary conditions with &ggr;=1.4. The solutions are obtained analytically in that part of the flow field not involving viscosity, and numerically in the other parts of the flow field. It is found that whereas all discontinuities of the physical parameters are removed by the viscosity there remain discontinuities in the slopes of these parameters at the shock front. It is indicated, moreover, that the complete flow field depends upon the form and magnitude of the viscosity.

ISSN:0021-8979    

DOI:10.1063/1.1722144

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The method of a previous paper is applied to the reflection and refraction of a weak spherical or cylindrical shock wave at a plane interface and by a plane slab. The method is also extended to apply to the diffracted wave which appears in these problems whenever total reflection occurs. From the results the leading terms in the asymptotic expansions for high frequency of the fields produced by periodic point or line sources over a plane interface are also obtained. These terms, which apply to electromagnetic as well as acoustic fields, are in exact agreement with results previously obtained by much more complicated methods.

ISSN:0021-8979    

DOI:10.1063/1.1722145

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The position and width of the x‐ray beam transmitted through calcite in Laue diffraction has been measured. For the extinction case, the transmitted beam has the same position and width as the incident beam. For the anomalous transmission case, the transmitted beam widens showing that the radiation propagates through the crystal along the diffracting planes. These results are in general accord with the theoretical calculations of von Laue.

ISSN:0021-8979    

DOI:10.1063/1.1722146

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The absence of weak detonations in available experience is felt to pose a problem since the well‐known rapid condensation processes encountered in the flow of expanding gases have all the characteristics and present, in fact, examples of weak detonations. As such, they would suggest that the initiation mechanism producing weak detonations will have to be different from that commonly adopted for strong detonations. The physical aspects of rapid condensation processes are discussed and compared with the conditions obtained by Friedrichs for the existence of weak detonations.

ISSN:0021-8979    

DOI:10.1063/1.1722147

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Techniques for the preparation by vacuum evaporation of single thin layers and laminated structures of ferromagnetic alloys (principally in the iron‐nickel system) are described. The magnetic properties are related to those parameters of the process which may be chosen to yield materials having desired characteristics. A method for producing films with extreme hysteresis loop rectangularity is described. Questions of suitable substrate materials, evaporable dielectrics for use in insulating multilayer deposits, and control of alloy composition, are considered in detail.

ISSN:0021-8979    

DOI:10.1063/1.1722148

出版商:AIP    

年代:1955

数据来源: AIP