摘要:

Secondary positive ions ejected from surfaces of Mo, Ta, and Pt under bombardment by inert gas ions of low energy (<1000 ev) have been studied in high vacuum (≤10−8mm of Hg of background gases) using a 60° sector field mass spectrometer with a 6‐in. radius of curvature, the object being to explore this as a technique for investigating solid surfaces in general. Ion species characteristic of the base metal, of surface compounds, and of a few bulk impurities were found. Quantitative analyses based on abundance ratios of the ions are unreliable, however owing to the enormous and essentially unknown differences in ionization efficiencies for the various species. Application of the technique to the investigation of surface kinetics seems highly promising, and as an illustration certain observations on the formation of PtO3on a Pt surface and its desorption at high temperatures are presented. Another possible application is to the study of sputtering, although some of the properties of secondary ions are shown to be quite different from those of sputtered particles in general. The secondary ions characteristic of the base metal comprise only a small fraction (0.01% for Pt) of the total sputtering yield, are principally singly charged and monatomic, have a low average energy (4–5 ev) and energy spread, and may result either from physical sputtering of the base metal or from the dissociation of surface compounds or both.

ISSN:0021-8979    

DOI:10.1063/1.1734952

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The principles of parametric amplification are described through the use of simple low‐frequency electrical circuits and their mechanical analogs. Extension of these principles to low‐noise amplification at microwave frequencies is made in a qualitative way which emphasizes the physical processes involved. Amplification is only achieved when energy is transferred from a microwave oscillator or pump to the signal frequency, and it is shown why such a transfer may take place in circuits exhibiting variable capacitance or inductance but not in circuits where only a resistance is varied. Major noise sources are discussed and the special role of the image or idler frequency is noted. Finally, experimental data on four different types of parametric amplifier (3 using semiconductor diodes and 1 using ferrite) are given.

ISSN:0021-8979    

DOI:10.1063/1.1734980

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The basic problems can be summarized in terms of (a) the internal kinematics, including the factors tending to dissipate the system or degrade its energy; (b) the stability of the system as a whole; (c) the initial formation, which in the view adopted here, is to be done by injection in an external magnetic field, or by some repetitive cycle of injection, acceleration and storage. Item (a) involves Coulomb scattering, especially multiple, and radiation arising from motion in the total field. The losses are described in terms of equivalent injection currents necessary to maintain a fictitious system with arbitrarily prescribed characteristics. Item (b) is discussed, mainly with reference to the ``kink'' instability in terms of a dynamical analogue, the breakdown of which leads to a formulation of the usually accepted necessary condition for stability. A stronger condition is also suggested, which, however, is probably much more than sufficient. The experimental difficulties of item (c) are discussed in only a general way, with no definite conclusions being drawn.

ISSN:0021-8979    

DOI:10.1063/1.1734965

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Collision experiments with He 23S and Ne3P metastable atoms are described, giving the total collision cross sections of these atoms with He, Ne, A at thermal energies, also the absorption cross sections of resonance photons from the He, Ne discharges.The secondary electron yields from He metastable atoms and from resonance photons incident upon W, Mo, Pt surfaces flashed to 1700°C are compared with the yields from an unflashed Au surface, previously determined absolutely. The rate of rise of yield due to gas contamination is examined. The yields from the flashed surfaces are found to be distinctly smaller than Hagstrum's yields for low‐energy positive ions.

ISSN:0021-8979    

DOI:10.1063/1.1734966

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Ion‐atom charge exchange cross sections of incident ion velocityvin the adiabatic region are shown to be proportional to exp (−K′a|&Dgr;E|/v) energy defect &Dgr;E.Maximum cross sections of the negative ion‐atom detachment collision and certain other inelastic ion‐atom collisions are shown to be proportional to the maximum kinetic energy available for internal excitation, ½&mgr;v2, where &mgr; is the reduced mass of the system. The semiempirical prediction of cross‐section energy dependence is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1734967

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

At nonrelativistic energies, for arbitrarily complicated collisions of distinguishable or indistinguishable particles, with or without rearrangement, correct formal expressions for the cross sections are known and well established. Nonetheless, all inelastic collision cross sections must be estimated, rather than predicted accurately, because even with present high spread computers there is no three‐or‐more particle collision for which it is practical to solve the Schroedinger equation exactly. The validity of the customary Born approximation, and of other more elaborate approximate calculations, are discussed, mainly with reference to electron excitation cross sections. The evidence suggests that a ``compound ion model'' of excitation, which is contrasted with the more usual ``direct interaction model,'' may prove helpful in understanding the sharp peaks and other anomalous features in some excitation cross sections near threshold. It is argued briefly that (i) there are reasons to think that at high energies Born approximation is not valid for exchange amplitudes, which are the only amplitudes appearing in excitation involving change of spin multiplicity; (ii) there are circumstances when Born approximation becomes increasingly valid as the incident electron energy is decreased.

ISSN:0021-8979    

DOI:10.1063/1.1734968

出版商:AIP    

年代:1959

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1734969

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The maximum values of the real and imaginary components of the paramagnetic susceptibility of a three‐level solid state maser are calculated. For the case of K3Co(CN)6paramagnetic salt with 0.5% Cr, the values &khgr;max′=2.5×10−4and &khgr;max″=5×10−4are obtained. General expressions for the gain and band width of a traveling wave maser are given. An analogy is brought up between the quality factorQper unit length of wave guide in the traveling wave maser and theQin the cavity maser.

ISSN:0021-8979    

DOI:10.1063/1.1734970

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The elastic constants of thorium single crystals have been determined at ultrasonic frequencies employing both resonance and pulse‐echo techniques. The values at 300°K in units of 1011dyne/cm2are,C11=7.53,C12=4.89, andC44=4.78. The constantsC11andC44increase andC12decreases with decreasing temperature and extrapolate to 7.79, 4.82, and 5.13, respectively, at 0°K. The Cauchy relationC12=C44occurs, quite probably fortuitously, at 271°K. The anisotropy factor 2C44/(C11–C12) at room temperature is 3.6 which is comparable to the values for lead and gold. Calculated Poisson's ratios, &sgr;100and &sgr;111, indicate a much stronger resistance to contraction in the close‐packed planes than in the less densely packed (100) planes.

ISSN:0021-8979    

DOI:10.1063/1.1734971

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The measurement of the stored energy of graphite taken from the lattice of the ORNL Graphite Reactor is described. The release of 26 cal/g of stored energy was observed upon heating to 218°C. The measurements were made using a new technique that depends upon the transfer of heat by radiation from the walls of the calorimeter to the sample.

ISSN:0021-8979    

DOI:10.1063/1.1734972

出版商:AIP    

年代:1959

数据来源: AIP