Volume 31, Issue 3, 01 March 1960
Index of content:
31(1960); http://dx.doi.org/10.1063/1.1735605View Description Hide Description
Sputtering ratios for copper have been determined in the energy ranges 5–40 kev for bombardment by Ar+, He+, and D+. Argon values range from 6.48 at 5 kev to 9.25 at 27.5 kev, deuterium from 0.048 at 10 kev to 0.023 at 44 kev, and helium from 0.23 at 15 kev to 0.75 at 40 kev.
Preliminary data are included for 30‐kev sputtering of copper by H+(0.011), D+(0.03), He+(0.13), N+(5.28), Ne+(3.61), Ar+(9.02), CU+(9.60), Kr+(15.15), and U+(20.9). Also included are sputtering ratios at 30 kev for Ar+ on Ta(2.7), Mo(3.31), and Al(2.38). Most of these data are the result of a single measurement, and require further verification.
A definite pressure dependence of the sputtering ratio for Ar+ on Cu was found in the range of 0.04 to 0.08 μ.
31(1960); http://dx.doi.org/10.1063/1.1735606View Description Hide Description
The measurements of electrical charges on dust clouds of crushed KCl monocrystals previously irradiated with β rays shows that the value of the mean charge depends on irradiation time. In the case of KCl irradiated with β rays, a photoelectric effect is not observed, despite the presence of F centers.
31(1960); http://dx.doi.org/10.1063/1.1735607View Description Hide Description
Macroscopic equations for conservation of charge, momentum, and energy, as derived from the Boltzmann equation, are applied to an electron stream having a velocity spread. For small velocity spreads, these equations are simple to treat. The noise parameters, S and Π, which determine the minimum noise figure of a beam‐type microwave tube, lose their invariance in the presence of velocity spread; they become functions of position. The changes of S and Π are such as to lower the minimum noise figure. These results are in agreement with a detailed numerical solution of the Boltzmann equation as previously reported by others.
31(1960); http://dx.doi.org/10.1063/1.1735608View Description Hide Description
The problem of forming molecular beams for use in ammonia masers is examined. It is shown theoretically and experimentally that through the use of a new type of parabolic focuser with a ``point source'' effuser, the molecular flow may either be reduced by a factor of 8, for the same power output, or the power output may be increased by a factor of 2 for the same molecular flow. A theory of beam formation in a multitube effuser is described. This shows that the most intense molecular beam is formed by an effuser of small overall diameter. Design considerations are discussed for parabolic, upper‐state focusers, and for coaxial, lower‐state focusers. The operation of a system is described, using a lower‐state focuser and an ionizationdetector, in which lower‐state molecules produced by maser oscillation may be detected.
31(1960); http://dx.doi.org/10.1063/1.1735609View Description Hide Description
The characteristics of molecular beams formed by sources consisting of long tube arrays are measured for several sources. The peak beam intensity and the beam width are calculated when collisions in the source are taken into account under the assumption that a limited region of Knudsen type flow occurs near the low‐pressure end of the source. The peak beam intensity and the beam width are calculated to vary as the square root of the total flow rate for source pressures giving useful directivity, in good agreement with the observations. Considerations in the design of sources are discussed.
31(1960); http://dx.doi.org/10.1063/1.1735610View Description Hide Description
The impact of aluminum projectiles on steel plates for impactvelocities of 2500 m/sec to 3000 m/sec and about 1100 m/sec was studied. Crater volume and penetration were measured. Shock wavevelocity from the free surface was determined and the particle velocity calculated. For annealed 4130 steel plates impacted at 2750 m/sec average velocity, the average free surfaceparticle velocity was 0.205 mm/μsec. Existing theory on cratering and penetration gave excellent agreement with the observed values.
31(1960); http://dx.doi.org/10.1063/1.1735611View Description Hide Description
By using the optical grid method the diffraction of water waves from circular and elliptic cylinders were measured and compared with theory. The scattered wave intensity S and the total energy scattered per sec per unit intensity Q were measured and the results bear out the well‐known fact that for angles less than 30 deg or in the vicinity of 180 deg, one cannot separate out the scattered wave and the incident plane wave.
The optical grid method is described in detail and the advantage of its being able to measure the instantaneous field emphasized.
31(1960); http://dx.doi.org/10.1063/1.1735612View Description Hide Description
A pump signal propagating along a dispersionless transmission line with a distributed nonlinear capacitance is subject to deformation, since different parts of the signal move with different velocities. This process of deformation will eventually result in the formation of an electromagneticshock wave. The deformation will affect the parametric amplification process. If a small signal consisting of a positive pulse, short compared to the pump cycle, is added to the pump signal at the input end, then it is shown that the small signal at the output must be non‐negative. All other small signals, including in particular those with sinusoidal time variation, can be regarded as superpositions of these short pulses. As a consequence it is shown that, in general, a sinusoidal signal will not be increased in its fundamental frequency component, by traveling down the line together with the pump signal. There are certain exceptional frequencies, multiples of one half the pump frequency, where a suitably phased small signal may be increased at its fundamental frequency, but not by a sufficient amount to be of practical interest.
31(1960); http://dx.doi.org/10.1063/1.1735614View Description Hide Description
The ``steady‐state'' creep of Al2O3single crystals was investigated. The experimental data are analyzed according to three mechanisms: the dislocation climb mechanism, the micro‐creep mechanism, and the Peierls stress mechanism. It is shown that the dislocation climb mechanism fits experimental data best. The expectation that Peierls stress mechanism is rate controlling in the ``steady‐state'' creep of Al2O3 is ungrounded.
31(1960); http://dx.doi.org/10.1063/1.1735615View Description Hide Description
Direct observations of interfacial growth and the approach of centers between spheres of sodium chloride were made in an argon atmosphere and over a temperature range of 700 to 800°C. The rate law governing the increase of the contact area between spheres, the effect of changing size scale on this rate and the absence of a change in the center‐to‐center distance during sintering all indicate that the rate‐determining mechanism of material transport in this sintering process is evaporation‐condensation. A model is presented which considers Stefan flow to occur within a thin boundary layer in the gaseous phase adjacent to the condensing surface, the sintering rate being predominantly governed by the rate at which sodium chloride vapor diffuses through this boundary layer. The marked pressure‐dependence of the empirical relationship between contact area and sintering time for fixed temperature and sphere size is consistent with the proposed model.
31(1960); http://dx.doi.org/10.1063/1.1735616View Description Hide Description
An apparatus has been developed to measure the effect of pressure to over 50 000 atmospheres on the decay rate of phosphors. Three manganese activated phosphors with exponential decay curves were studied. In two cases the rate of decay decreased, in the third case it increased. A tentative explanation is offered. An hexagonal ZnS:Cu phosphor showed little pressure effect to 40 000 atmospheres at which pressure it transformed irreversibly to the cubic form with a sharp increase in decay rate and a large decrease in intensity.
31(1960); http://dx.doi.org/10.1063/1.1735617View Description Hide Description
The thermal conductivity,electrical resistivity, Lorenz number, thermoelectric force, and thermoelectric power are given in the temperature range 4–120°K for ten aluminums and aluminum alloys: high‐purity, 1100‐F, 1100‐O, 3003‐F, 2024‐T4, 5052‐O, 5083‐O, 5086‐F, 5154‐O, and 6063‐T5. Four of the samples show a maximum in thermal conductivity, the others do not. For the four high‐thermal conductivity samples the separate components in the electronic thermal resistivity are resolved; for the others, components in both the electronic and the lattice thermal resistivities are given. The residual electrical resistivities vary from 2.5×10−8 to 3.2×10−6 ohm cm. The Lorenz numbers for the high‐conductivity samples fall considerably below the Sommerfeld value 2.44×10−8 watt‐ohm/°K2; those for the low‐conductivity samples are somewhat above the Sommerfeld value. The thermoelectric power of some of the the alloys is positive with respect to the high‐purity sample, for others it is negative. The various properties, methods of analysis, and separation of components are discussed in detail.
31(1960); http://dx.doi.org/10.1063/1.1735618View Description Hide Description
The thermal conductivity,electrical resistivity, and Lorenz number are given in the temperature range 4–100°K for the widely used thermocouple wire, gold‐2.1 atomic percent cobalt alloy. The total thermal conductivity is relatively low: from 0.01 watt/cm°K at 4°K to 0.23 at 100°K. The lattice contribution to the total thermal conductivity is larger than the electronic contribution. The electrical resistivity is nearly independent of temperature, but does have a definite minimum of about 1.20×10−5 ohm‐cm at 30°K. Because of the relatively large contribution of the lattice term to the total thermal conductivity, the Lorenz number is considerably above the electronic Sommerfeld value, 2.44×10−8 watt‐ohm/°K2.
31(1960); http://dx.doi.org/10.1063/1.1735619View Description Hide Description
Experimental noise and signal response data of two lead sulfide photoconductive films have been obtained as a function of frequency and radiation wavelength at temperatures ranging from about 25°C to −173°C. Good agreement between experiment and a theory proposed by Petritz is found. The theory is used in such a way that correlations between noise and response may be made independent of the temperature. The measured time constants enter into the correlations only indirectly; they are necessary only to extrapolate data measured at a given frequency to some lower frequency. Generation‐recombination (G‐R) noise predominates at all temperatures. Time constants measured by noise and by response agree. The role of absorbed ambient photons is described. These photons are important at the lower temperatures. The concentrations of the majority carriers (holes) and their mobility as derived from signal data are listed.
31(1960); http://dx.doi.org/10.1063/1.1735620View Description Hide Description
The ``ultimate'' electron density in the negative glowplasma of a cold‐cathode discharge in helium at gas pressures 3–12 mm Hg has been determined by simultaneous Langmuir probe and microwave transmission methods. A correlation is obtained at densities above ∼4×1011/cm3 when the influence of positive ion scattering of the electrons diffusing to the probe is considered. The ultimate electron temperature in the helium negative glow was measured by the metallic probe to be quite low, ∼400°K, and the ``secondary'' electron temperature was found to be ∼50 000°K. These probe indications are substantiated by measurement of the microwave noise power radiated from the plasma which is found to correspond to an effective temperature varying from 300 to ∼1000°K.
31(1960); http://dx.doi.org/10.1063/1.1735621View Description Hide Description
The results are reported of an investigation of quenched‐in prismatic dislocation loops in super‐purity aluminum. Some new effects have been observed: in particular, that loops tend to be grouped in clusters containing a surplus of loops of one orientation; that more than four loop orientations are realized; and that often pairs of similarly oriented and similarly shaped loops are present in the quenched material. It is concluded that vacancies aggregate into three dimensional clusters, containing from a few to a few hundred or even thousand vacancies, before being converted into prismatic loops.
Numerical Calculation of Absolute Bremsstrahlung Intensity for a Fully Ionized Fully Dissociated Hydrogenic Gas31(1960); http://dx.doi.org/10.1063/1.1735622View Description Hide Description
By using the approximate relationships of Kirkpatrick and Weidmann [Phys. Rev. 67, 321 (1945)] for bremsstrahlung intensities, numerical calculations have been made on the IBM 650 at the Avco‐Everett Research Laboratory for a fully ionized, fully dissociated hydrogenic gas. The intensities are given in terms of a quantity having the units ergs/sec/unit frequency interval/steradian/cm3 as a function of hv, (from 0.5 to 4.0 ev) and kT (from 4 to 200 ev). A calibration method has been devised for measurement of absolute bremsstrahlung intensities which continually compensates for the errors present in most calibration procedures.
Effect of Fast Neutron Bombardment at Various Temperatures upon the Young's Modulus and Internal Friction of Copper31(1960); http://dx.doi.org/10.1063/1.1735623View Description Hide Description
Studies have been made of the variations of internal friction and elastic modulus during irradiation of pure copper crystals at a number of temperatures in the range 90°K to 300°K. The results are interpreted in terms of pinning of dislocation lines by radiation defects migrating from their points of origin. In terms of the room temperature value the dislocation pinning rate is 2.5×10−2 in the range 100°K to 140°K and (from previous measurements) of the order of 2.5×10−5 at 20°K. On slowly warming the sample after the irradiation, it is found that at 260°K the modulus and decrement begin to move rapidly toward their ``saturation'' values. Presumably, defects ``stored'' in the sample due to a lack of thermal mobility at the irradiation temperature become mobile at this temperature and move to the dislocation lines.
31(1960); http://dx.doi.org/10.1063/1.1735624View Description Hide Description
Highly axially oriented fibers of linear polyethylene are shown to display four orders of well defined, meridionally directed diffraction maxima corresponding to a fundamental spacing of 408 A. An interpretation of the low angle x‐ray pattern is given in terms of the fiber morphology and the Hess‐Kiessig postulate as to the origin of the periodic variation in electron density. The relative macroscopic length of the fibers was systematically altered both by thermal treatment and by crosslinking, melting, and recrystallization. The magnitude of the spacings observed does not bear any direct relation to the change in length incurred, but reflects the change in crystallite size that develops because of annealing,partial melting or the introduction of crosslinks. It is also shown that in a completely shrunken fiber, where wide‐angle x‐ray diffraction shows that the crystallites are randomly arranged relative to one another, discrete diffraction maxima are observed at about 255 A. These maxima are, however, circular in shape. Intermediate types of line shapes are also observed, which depend solely on the crystallite orientation and not on the method by which the orientation is developed.
31(1960); http://dx.doi.org/10.1063/1.1735625View Description Hide Description
A study of the reflection of underwater sound from nonperiodic, pressure release surfaces is reported. The Eckart theory for wave reflection from rough surfaces has been adapted (with some modifications) to the experimental work. A portion of the investigation was directed toward a study of the dependence of the intensity reflected in the specular direction on angle of incidence, radiation wave number and the statistics of the reflecting surface. Secondly, a method is illustrated for determination of the rms amplitude and the correlation function of the reflecting surface from an analysis of the reflected intensity distribution. The radiation wavelength, in this case, must be much larger than the rms roughness amplitude.