摘要:

The depth of penetration of 0.5‐ to 11‐kev electrons and 1‐ to 25‐kev H+, H2+, and He+ions in aluminum has been measured. It has been found that the Thompson‐Whiddington law for electrons does not hold for electrons having energies less than 10 kev. The practical range‐energy relation obtained for electrons in aluminum was found to beR = KE1.3, whereKis 0.042 ifEis expressed in kev andRin microns. The practical range‐energy relation for light ions in aluminum was found to beR = KE0.83whereK= 0.020 for H+,K= 0.021 for He+, andK= 0.015 for H2+ifEis expressed in kev andRin microns. Results are compared with those obtained by previous observers.

ISSN:0021-8979    

DOI:10.1063/1.1722186

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Plasma oscillations are here treated for a frequency range having application not only to gaseous discharges but also to solids such as impurity semiconductors.Amplification of longitudinal electrostatic waves in a plasma may be achieved through energy exchange with a synchronously traveling electron beam, this being the same mechanism which underlies amplification in the traveling‐wave tube. The dispersion equation describing this beam‐plasma interaction, first derived by Bohm and Gross, is studied systematically to obtain the characteristics of the growth‐in‐time, &ohgr;vs&kgr;, of standing plasma waves and the complex propagation constant &kgr;vs&ohgr; for traveling plasma waves, at extremely high frequencies (high plasma densities). The problem of collision damping is also discussed. The possible application of plasma oscillations to the solution of the problem of the generation of millimeter wave power is considered, both for plasmas in gaseous discharges and for the thermally generated plasmas in impurity semiconductors.

ISSN:0021-8979    

DOI:10.1063/1.1722195

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A new method of suspending a molten zone is as follows: clamp a horizontal cylindrical ingot at both ends; apply a horizontal magnetic field normal to the ingot where the zone is to be suspended; and pass a direct current through the ingot, creating an upward force equal and opposite to the gravitational force, thereby permitting the zone to be melted and suspended. It is shown theoretically that such a zone will be stable in a uniform magnetic field if its length‐to‐diameter ratio is less than &pgr; and if its length is less than 0.17(&ggr;/&rgr;)½, where &ggr; and &rgr; denote surface tension and density, respectively, in cgs units. Some experimental results and practical considerations are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1722187

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The yield of photoneutrons from a sample of U235fission products at the center of a 9‐in. diameter Be sphere was measured. Samples of U235were exposed to neutrons in the reactor for periods of 15 min, 6 hr, and 74 hr. The photoneutrons created by the fission product gamma rays acting upon the Be nuclei were observed from 0.3 sec to about 4 weeks after the end of the exposure. Curves showing the photoneutron yield as a function of time, relative to the delayed neutron yield, are given for these exposure and observation times. The attempt was made to account for the observed yields from Be in this experiment, and the yield from D2O observed in an earlier experiment, in terms of known fission product gamma emitters.

ISSN:0021-8979    

DOI:10.1063/1.1722188

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The yield of photoneutrons from U235, U233, and Pu239fission products in heavy water were compared. The number of photoneutrons per delayed neutron was found to be approximately the same for all three, in spite of the previously known large variations in the relative numbers of delayed neutrons from these isotopes.

ISSN:0021-8979    

DOI:10.1063/1.1722189

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The constitutive dielectric parameters for uniform space arrays of generalized structural geometry composed of similarly oriented elements of completely generalized material and shape are derived. The theoretical procedure employed in evaluating these parameters is analogous to the classical method applied to the study of the dielectric properties of nonpolar media and assumes that the disturbing action of each particle on a uniform static field can be allowed for, if each particle is replaced by a set of dipoles. Consequently, the results are applicable to microwave frequencies only if the cross‐sectional dimensions and interelemental spacings remain small compared to the wavelength. The general result is particularized for the case in which the elements are spherical objects with a tensor permeability and scalar dielectric constant. The results have several applications to the design of artificial dielectrics and some of these are given.

ISSN:0021-8979    

DOI:10.1063/1.1722190

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Short field emission arcs are of two types, those which vaporize metal predominantly from the anode by electron bombardment, and those in which the metal of the arc is supplied from the cathode largely by the melting of points by the field emission currents flowing through them. These are appropriately called ``anode arcs'' and ``cathode arcs.'' A single anode arc erodes a pit in the anode and leaves a corresponding roughened area on the cathode. A single cathode arc, on the other hand, leaves on the cathode a widely dispersed array of individual pits which tend strongly to lie along scratch lines; in many cases no mark at all can be found on the anode after an arc of this type. Anode and cathode arcs differ in arc voltage, which is higher for cathode arcs than for anode arcs, and in other ways. Both types of arcs have been observed for many metals, but the data reported here are for palladium only. For clean surfaces of palladium all arcs are of the cathode type at a striking potential of 400 volts, but at 300 volts and at lower voltages anode arcs are observed also, becoming more frequent as the voltage is lowered. For surfaces activated by carbonaceous material only arcs of the cathode type occur at all striking potentials. In an anode arc, metal is transferred in both directions, as measured by radioactive tracers, but the net transfer is from anode to cathode. A cathode arc transfers metal from cathode to anode only, and the magnitude per unit of arc energy is less than the transfer in an anode arc.

ISSN:0021-8979    

DOI:10.1063/1.1722191

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Neutron irradiation effects in the precipitation hardening alloy, nickel‐beryllium, were measured using the ferromagnetic Curie temperature as an index of the amount of precipitate formed. Effects found previously in a similar precipitation hardening alloy, copper‐beryllium, were not found upon irradiation at approximately room temperature. However, an irradiation for an integrated fast flux of 4×1017n/cm2at a temperature of 300°C showed that 1.3 atomic percent more beryllium in the form of the compound Ni&sngbnd;Be precipitated from a supersaturated solid solution than from a similar specimen held at 300°C but not irradiated.

ISSN:0021-8979    

DOI:10.1063/1.1722192

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

It is proved that any network of linearly wound potentiometers and fixed resistors has a curve of resistanceversusshaft angle which is concave downward.

ISSN:0021-8979    

DOI:10.1063/1.1722193

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

An attempt is made to show that the highly localized temperature and associated thermal stress gradients in front of active slip planes, resulting from the conversion into heat of the work in slip of the resolved shear stress, are of sufficient severity to account for the initiation of micro‐cracks parallel to the slip planes if, as in fatigue, slip under repeated stress cycles is concentrated into ``striations.'' The effect of the thermal characteristics of the metal on its fatigue performance is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1722194

出版商:AIP    

年代:1956

数据来源: AIP