Volume 30, Issue 12, 01 December 1959
Index of content:
30(1959); http://dx.doi.org/10.1063/1.1735079View Description Hide Description
Measurements of the white noise of transistors (principally, diffused‐base structures) and diodes have been made at temperatures ranging from ∼77°K to 300°K for a range of about two decades in injection level, and from 10 kc to 10 Mc. Comparisons of the noise measurements with calculated levels are presented. The germaniumtransistors show a progressively increasing deviation from the theory as the temperature is decreased, and most of the silicontransistors exhibited excess white noise at room temperature and below.
30(1959); http://dx.doi.org/10.1063/1.1735080View Description Hide Description
A theoretical description of sinusoidal oscillation of an incompressible viscoelastic medium between fixed infinite parallel planes is presented. The mechanical properties of the viscoelastic medium under sinusoidal shear are expressed by a complex viscosity coefficient. The general equation for oscillatory motion of an incompressible viscoelastic medium is developed. The solution to this equation is obtained for rectilinear motion parallel to a pair of infinite planes. The equation for the velocity distribution between the planes is developed and several typical profiles are presented graphically. The equation for the acoustic impedance per unit area of plane is obtained. Functions from which the acoustic resistance and acoustic reactance may be determined are presented in graphical form for media which range from a perfect viscous fluid to a perfect elastic solid. The applicability of the theoretical results to oscillatory flow in rectangular tubes is discussed.
30(1959); http://dx.doi.org/10.1063/1.1735081View Description Hide Description
The operation of a cesium plasmathermocouple is described for a range of hot‐junction temperatures from 1600°K to 2600°K and for a range of cesium pressures from 10−5 mm Hg to 2 mm Hg. Electromotive force and short‐circuit current data are presented for cells containing three different emitter substances: Ta, ZrC, and (ZrC) (UC). In the range of pressure and temperature variation studied, the observed electromotive forces are between 1 and 4.5 volts. Short‐circuit current depends markedly on the current emission properties of the hot electrode. The largest short‐circuit current density observed for the (ZrC) (UC) emitter, is 62 amperes per square centimeter.
30(1959); http://dx.doi.org/10.1063/1.1735082View Description Hide Description
Some experimental studies of a cold cathode discharge in a strong magnetic field are described. Current densities of the order of half an ampere per square centimeter in various gases were used. For such a discharge, the current to the cathodes is about 75% ionic. Positive ions leaving the discharge by moving across the magnetic field were observed with a mass spectrometer and showed a temperature of about 1 v. Fast electrons from the cathode escape from the discharge across the magnetic field without losing the greater part of their energy. By considering the rate of ion production it is shown that the slow electrons in the discharge have a temperature less than about three volts. Fluctuations in charge densities must play a very important role in the mechanism of the discharge.
30(1959); http://dx.doi.org/10.1063/1.1735083View Description Hide Description
A new method is described for recording electrical signals. Information is written at extremely high density by means of an electron beam on a film consisting of a low melting thermoplastic material. This can be projected as a full color image, or can be converted to an electrical signal. The tape, which is processed by quick heating, can be readily erased and reused.
30(1959); http://dx.doi.org/10.1063/1.1735084View Description Hide Description
A very low friction, about 10−2, has been unexpectedly observed in reciprocating sliding with gold,silver,copper, and platinum. It was found that the characteristics common to those metals were soft metal substrate and no surface oxide or soft oxide. Some discussion is given on this phenomenon.
30(1959); http://dx.doi.org/10.1063/1.1735085View Description Hide Description
The characteristics of noise propagation through a multi‐velocity region with linearly increasing dc potential have been calculated using the density‐function formulation of Siegman, Watkins, and Hsieh. [J. Appl. Phys. 28, 1138 (1957)]. This type of noisetransducer approximates that found experimentally in electron guns which have produced noise figures of 3 db and less at S band. It is shown that arbitrarily low values of beam noisiness can be obtained by reducing the slope of the potential profile and that adjustment of this parameter provides the practical possibility of attaining very low noise figures in slow space‐charge wave amplifiers as frequency is increased. The calculated results are compared with experimental data at S band and X band.
30(1959); http://dx.doi.org/10.1063/1.1735086View Description Hide Description
Studies are presented showing the electrical properties of the highly ionized, detonation‐generated plasmas ejected into various gaseous media at the bare surfaces of high explosives. These externalplasmas are shown to originate from chemionization in the reactions of high explosive at free surfaces and are not produced by thermal ionization in the shock wave propagated in the surrounding gaseous medium. The initial external‐plasma length Lp * was found to be directly proportional to the length a 0 of the reaction zone of the high explosive‐generating source. Conduction measurements in plasmas propagating in chlorine, oxygen, argon, nitrogen, helium, and air showed that the electron affinity of the gaseous medium is important in determining the rate of decay of the plasma and its ultimate disintegration. The lifetime of external plasmas are substantial in media of low electron affinity, exceeding appreciably 250 μsec in such media as argon, helium, and nitrogen. Free electrons contribute practically the entire conductivity of these plasmas. Interesting pulsations occur when the external plasmas are generated by a charge of diameter smaller than the constraining tube and upon passing from a smaller into a larger constraining tube. A striking confirmation of the quasi‐lattice or metallic‐like model of plasmas is the observation that the plasma finally ``explodes'' into a gas cloud many times larger when its ion density decays to a critical low level.
30(1959); http://dx.doi.org/10.1063/1.1735087View Description Hide Description
By exposing with light flashes delayed by short time intervals after the application of electric field pulses, it is possible to measureionic conduction on large silver bromide grains from a photographic emulsion. Values of conductivity were obtained by an analysis of the transient decay of internal field pulses resulting from the application of known pulses of the external field. The internal field was measured by means of its effect in causing displacement of latent‐image centers formed by the exposure flashes. The room‐temperature ionic conductance of these grains was found to be the equivalent of about 9×10−6Ω−1 cm−1 with an activation energy of about 0.42 ev. This conductance is several powers of ten higher than that reported for large silver bromide crystals of high purity and is thought to be primarily the result of surface effects. The implications of this result in terms of modern theories of photographic latent‐image formation are discussed.
30(1959); http://dx.doi.org/10.1063/1.1735088View Description Hide Description
Pulses of electric field applied to silver bromide grains of a photographic emulsion at short time intervals after the application of short light flashes cause displacement of photoelectrons and holes if their lifetimes are greater than the delay interval. The asymmetry in the location of the photoproducts—microscopically visible silver and bromine or developable latent‐image specks—is an indication of the fraction of carriers free at the time the electric field is applied. As the delay interval is varied, the decay of the number of free carriers may be followed. In the emulsion system studied, the number of photoelectrons was found to decay approximately according to a 1/(1+αt) law, falling to half the initial value in 0.25 μsec. The lack of a dependence on intensity or temperature is taken to indicate temporary trapping in a distribution of shallow traps, perhaps at the grain surface. The number of free holes decays by an exponential law, with a mean lifetime of about 15 μsec. Indications are that hole mobility is very low, owing either to temporary trapping or self‐trapping. The implications of these results in terms of modern theories of latent‐image formation are discussed.
30(1959); http://dx.doi.org/10.1063/1.1735089View Description Hide Description
Observation of the deformation of thin aluminum specimens inside the transmission electron microscope has revealed the intimate connection between deformation and the nucleation and motion of dislocations. Nucleation, slip propagation, and the progress of deformation to the point of rupture have been observed visually on the fluorescent screen and photographed by both ``still'' and motion pucture techniques. In this way even the detailed predictions of the dislocation theory of deformation have been confirmed, and the new phenomena of grain boundaries acting as ``donors'' or ``acceptors'' of dislocations have been discovered.
30(1959); http://dx.doi.org/10.1063/1.1735090View Description Hide Description
The thermoelectric figure of merit z=α2/ρκ is calculated for an extrinsic semiconductor with mixed acoustic‐mode lattice scattering and ionized‐impurity scattering. The result is compared to the value for pure acoustic‐mode scattering. As the amount of ionized‐impurity scattering is increased, the figure of merit increases by less than 10% and then falls slowly.
30(1959); http://dx.doi.org/10.1063/1.1735091View Description Hide Description
The rocket optimization formulation of B.D. Fried is modified slightly to facilitate the study of maximum accuracy trajectories. Various illustrative special solutions are obtained, particularly perturbation results valid for small thrust. For surface‐to‐surface rockets in a Kepler field, optimal thrust programs are obtained numerically, their accuracy is studied quantitatively, and comparison of range and of accuracy is made with rockets using a constant‐angle thrust program. Optimization leads to only a slight increase in range but to a substantial gain in accuracy. The possible application of rocket optimization methods to the focusing of charged particles is also suggested.
30(1959); http://dx.doi.org/10.1063/1.1735092View Description Hide Description
Quantitative data are presented which show the relative contributions of wall motion and domain rotation to the magnetization reversal process in thin ferromagneticfilms for driving fields ranging from the coercivity to many times the anisotropy field. Also, an equation for the total magnetization reversal time is developed. This expression consists of two distinct components: one represents wall motion reversal time and the other reversal time due to domain rotation. The equation is similar to one published previously but contains a more realistic and more suitable wall nucleationdistribution function.
30(1959); http://dx.doi.org/10.1063/1.1735093View Description Hide Description
The characteristics of a germaniumsurface barrier diode operated at room temperature make it particularly useful as an alpha‐particle spectrometer. The small size, stability, energy resolution, and relative insensitivity to β and γ radiation of the units suggest applications in medical and nuclear research. Studies were made on Au–Ge and Au–Si surface barriers with a barrier width (≅1 μ) less than the range of the incident alpha particles. In the germanium units, the pulse‐height response to alpha particles increased linearly with energy up to 7.5 Mev and then increased monotonically but more slowly as the energy rose to 12 Mev. In silicon the deviation from linearity occurred around 6 Mev. The observed linearity between pulse height and energy depends simply on the fact that the number of carriers excited is proportional to the particle energy and that the time for the carriers to be collected at the barrier is less than the circuit time constant. The general theory of the transient response of the diode was developed and the calculated response compared with the observed behavior. The observed values of the energy required to create a hole‐electron pair, measured over the energy range of linear response of the junction, were ε(Ge)=2.96±0.1 ev and ε(Si)=3.9±0.3 ev.
30(1959); http://dx.doi.org/10.1063/1.1735094View Description Hide Description
The breakdown characteristics of two types of siliconp‐n junctions are studied. In the first type of junction which is commonly encountered, the breakdown occurs in many localized regions, the characteristic being determined by the aggregate effect of the localized regions; in the second type of junction the geometry is such that only one localized breakdown region occurs. Whereas the simple avalanche theory can explain the onset of breakdown for both types of junctions, the shape of the V‐I curve in the breakdown region cannot be explained without the inclusion of another variable in the theory. Experimental evidence obtained by the use of pulse techniques indicates that this variable is the temperature rise due to the current flowing through the junction. It is found that this self‐heating is the most important single factor in determining the shape of the V‐I curve and that almost the entire dynamic resistance in this region is due to this effect. A method is given for determining the temperature rise of the junctions, provided that the V‐Icharacteristic is known.
30(1959); http://dx.doi.org/10.1063/1.1735096View Description Hide Description
The method previously used to calculate the magnetization curve of an infinite cylinder is applied to the new Meiklejohn and Bean material which is made of Co particles in a CoO shell. It is assumed that the interface of the ferromagnetic and antiferromagnetic materials is held parallel to the cylindrical axis and does not change its direction for any value of the applied field. The crystal anisotropy is neglected.
It is shown that the easiest nucleation mode for small radii is buckling and for large radii is curling. The transition from buckling to curling is at about RIsA −½=2, where R is the radius of the cylinder, Is is the saturation magnetization and A is the exchange constant.
Numerical solution of the nonlinear equations involved, yields two branches in the magnetization curve, which are both stable with respect to curling perturbations. The general stability is not tested.
A similar calculation is carried out for an infinite slab with the spins on the surface held at a fixed direction and with the crystal anisotropy neglected.
30(1959); http://dx.doi.org/10.1063/1.1735097View Description Hide Description
30(1959); http://dx.doi.org/10.1063/1.1735098View Description Hide Description
X‐ray powder and rotation patterns of six cubic substances (W, Si, Cr, TiO, Al, and V) using specimens of different thickness were made; the patterns were measured, the lattice constants calculated and plotted against the θ angle or against the Nelson and Riley function. Such curves for thin mounts, semitransparent to x‐rays (below 0.2 mm in diam), consist of two parts: a region of high slope (due to absorption) and one approaching a zero slope at high Bragg angles. The latter, varying in extent with the size and nature of the mount, indicates that due to the rapid decrease in absorption, the lines in this region are shifted, little if any, from their correct positions. Hence, lattice constants calculated from the reflections of the high θ angles lying on the horizontal portion of the curve need not be corrected for absorption. The constant, with negligible error, can be calculated from a single last strong α1 or β reflection. If an extrapolation is applied, the curve must be traced through points in the high back reflection region. Otherwise any extrapolation, disregarding the horizontal part, would lead to lattice constants too high in value. The amount of line displacement due to absorption in thin samples (below 0.2 mm in diam) agrees with the geometrical concept of Hadding and Buerger.