摘要:

The activation of oxide cathodes by chemical impurities present in the base nickel is analyzed using classical diffusion theory and a model in which the concentration of donors in the oxide particles is controlled by alkaline earth metal adsorbed on the oxide particles. Strong surface adsorption of the alkaline earth metals on the oxide crystal surfaces is indicated. To fit calculated curves of average donor concentration to experimentally observed pulse emission data obtained on Ni with Al as an impurity, surface adsorption energies of 3.2 to 3.4 ev are indicated.

ISSN:0021-8979    

DOI:10.1063/1.1722602

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A study has been made of the domain structure of thin films (∼1000 A) of MnBi and their capability of storing information magnetically. It is estimated that a million bits of information could be written on a square centimeter of film. The information can be read out optically by utilizing the Faraday effect. The films have a uniaxial direction of easy magnetization normal to their surfaces and retain their magnetization after saturation along this direction in spite of the large demagnetizing factor. When magnetized in this manner, a high optical contrast is obtained between the writing and the background.

ISSN:0021-8979    

DOI:10.1063/1.1722603

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

An expression for the steady‐state creep rate of crystals is derived for the case where dislocation climb is not rate controlling. Two rate‐controlling processes are considered. In the first the dislocations are considered to move in a viscous manner, their velocity of motion being proportional to the force exerted on them. The second mechanism makes use of the Peierls stress. The Peierls stress mechanism can be used to explain the results of Gilman on creep by prismatic glide in high‐purity zinc. At low stresses the analysis for both processes leads to a power law stress dependence for the creep rate. The value of the exponent of the stress is approximately equal to three.

ISSN:0021-8979    

DOI:10.1063/1.1722604

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Electron backscattering measurements were carried out on composite layers consisting of thin metal films deposited on base layers of widely different backscattering properties. At low primary energies the backscattered fraction &eegr; (energies >50 ev) is found to be characteristic of the surface film. When the electron energy is such that the range in the surface material is equal to twice its thickness, a marked change in &eegr; occurs. At sufficiently high energies, &eegr; approaches the value for the base layer. Measurements of &eegr; as a function of energy were made for layers of Al&sngbnd;Au, Al&sngbnd;Ag, and Al&sngbnd;C. These results led to a new method for measuring &eegr; for insulators using thin aluminum surface films (∼200 A) to avoid charging. Data on LiF, Zn3(PO4)2, KCl, RbBr, and TlI above ∼5 kev indicated agreement with the known values for metals of the same average atomic number, demonstrating that backscattering in the kev range and above is an atomic characteristic independent of the crystal structure or the conduction properties of the solid.

ISSN:0021-8979    

DOI:10.1063/1.1722605

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Upon depoling ceramic barium titanate, up to 9% of the domains reorient by 90°, indicating that during poling at least this percentage of the domains was permanently reoriented by 90°. Ceramic barium titanate shows a strong anelastic effect in the ferroelectric state, presumably due to domain reorientations under stress. Application of tensile and compressive stresses causes up to 13% of the domains to change their orientation by 90°, but, unlike the electric case, no permenent domain reorientation is found. These domain switches are detected by x‐ray intensity and strain measurements. The agreement between the percent domain switches computed from the x‐ray data and that computed from the strain data is good in the case of mechanical compression, but not in the case of electrical and mechanical tension. In the latter case more domains appear to switch in the bulk than in the surface of the material. A space‐charge effect at the surface of ferroelectric barium titanate is suggested as a reason for this anomaly. Experimental evidence of the effect of grinding, etching, and irradiation on the domain orientation in the surface layer of ceramic barium titanate is cited.

ISSN:0021-8979    

DOI:10.1063/1.1722606

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Expressions are developed which give the amount of unidirectional radiation from a distant radiation source passing through a cylindrical hole in a slab of material, including the amount of radiation which penetrates the edges of the hole, as a function of angle between the radiation direction and the axis of the hole. The modifications necessary for sources at finite distances are indicated. These functions are integrated over appropriate angles for distant line sources, and for extended sources. It is shown that, to a first approximation, the results are the same as the geometrical aperture for a like diameter hole in a similar slab with one mean free path of material removed from each side. The effects due to scattering from the walls of the collimator are discussed and an approximate method of calculation is presented with results for a specific collimator.

ISSN:0021-8979    

DOI:10.1063/1.1722607

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

The spatial sensitivity pattern of a gamma‐ray collimator and NaI scintillation detector was explored with small radiation sources of three gamma‐ray energies (0.145 Mev, 1.12 Mev, 1.59 Mev). The collimator used was a cylindrical hole of ½ in. diam through 8 in. of lead. The results are compared with calculated patterns. The effects of penetration of the collimator edges are clearly shown.

ISSN:0021-8979    

DOI:10.1063/1.1722608

出版商:AIP    

年代:1957

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1722610

出版商:AIP    

年代:1957

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1722611

出版商:AIP    

年代:1957

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1722612

出版商:AIP    

年代:1957

数据来源: AIP