Table of contents

The solution of the electromagnetic flowmeter equation, with non-uniform magnetic induction and axisymmetric velocity and conductivity profiles, is given in the form of a convergent power series.

The ratio of saturation magnetization squared to wall energy, M_S²/γ, can readily be determined from domain size measurements on uniaxial platelets or films with large values of cprime (= cM_S²/γ, where c is the thickness). A graph is constructed from which this ratio can be found, even in the region of low cprime where there is no explicit relation between domain configuration and specimen thickness, and its use in the study of orthoferrites and garnet films is illustrated.

Neutron irradiation lowers the resistivity of diamonds to about 0·3 Ω cm after very heavy doses.

The basic criterion for the operation of the TRAPATT mode is examined, and limitations in existing theory are indicated. The results of a computer simulation indicate in particular that TRAPATT operation is possible at terminal current densities one order of magnitude less than previously thought possible; this is important in relation to CW as opposed to pulsed operation.

There is great interest in the behaviour of amorphous semiconductors, and considerable efforts are being made to devise theoretical interpretations of experimental observations. After a brief review of some of the experimental evidence, this paper discusses theoretical ideas concerning the electronic states and electrical transport in amorphous semiconductors being developed by various workers.

In this paper, photoelastic problems involving optical activity are analysed using Stokes parameters. A set of differential equations equivalent to the Maxwell-Neumann equations is derived which yields results with greater ease than other currently available methods. A few specific problems are solved by using these equations. A brief discussion on the use of scattered light methods in problems with optical activity is also included.

A cathode ray tube is used with a cathodochromic material carried either on a mica foil or on the faceplate of the tube. Some experiments are performed on the selective erasure of information by means of heat applied by electron bombardment. The energy density required to erase a spot and a line is measured. The pulse duration and dwell time are varied between 10 ms and 10 s. The results can be understood by use of the heat flow equation, and can be used to assess the possibility of selective erasure in a given configuration.

The performance of a transversely excited pulsed CO₂-N₂-He laser is examined at pressures up to 3 atm. The electrical discharge determines an optimum partial pressure of carbon dioxide plus nitrogen, which remains constant when the total gas pressure is varied.

Double heterostructure Ga_xAl_1−xAs-GaAs-Ga_x Al_1−xAs injection lasers have been made by multilayer solution epitaxy. Active region widths of less than 0·2 μm have been obtained, yielding threshold current densities down to 1000 A cm⁻² at 300 K, with incremental efficiencies up to 50%. The results are all in reasonable agreement with the theory of optical waveguides, although some quantitative discrepancies may be due to imperfect knowledge of the experimental conditions.

Emission polar diagrams became narrower when the width of the active region was decreased below 0·6 μm, showing that there was significant penetration of the optical field into the boundary regions when the optical waveguide was narrow.

The assumption that the noise properties of photomultipliers may be adequately represented by a single source with Poisson statistics is questioned in the light of the effects of correlated pulses and the possible presence of 1/f noise. The existence of this type of noise in an RCA 8850 photomultiplier has been demonstrated from measurements of the variance of the noise count rate. Its origin was investigated by measuring the variation of the intensity with voltage and temperature, and by observing the correlation with ion pulses in the tube.

The method of weighted residuals is used to produce approximate solutions to the integral form of the Boltzmann transport equation for thermal neutron fluxes near a moderator temperature discontinuity. Both spherical and plane geometries are considered. The validity of the technique is established by using a synthetic scattering kernel and making comparisons with exact transport theory solutions for two-temperature problems. The relative accuracy and importance of the choice of different weighting functions and of the number of trial modes in the flux expansion is investigated. Generally, it is found that using three or more maxwellian distributions for the energy trial modes of the flux produces a significant increase in the accuracy compared with a diffusion theory approximation.

A method for determination of the velocity distribution of a flowing material from the measured electric potential distribution is presented. The velocity distribution is expressed in polynomial form.

A generalized method is given for the measurement of the amplification coefficient g and the ratio of radial diffusion coefficient to experimental mobility, D_er/μ_exp, for electron swarms moving through uniform electric fields in the presence of secondary electrons. The technique requires the experimental measurement of both the current amplification and the radial distribution of anode current. Measurements are reported for swarms in hydrogen for 30<or=E/p₀<or=350 V cm⁻¹ Torr⁻¹ (at 0°C).

A method of calculating the voltage-current relationship and incremental resistance of a Townsend discharge having planar, cylindrical or spherical geometry is described. The method uses a result of Loeb (1953) to facilitate calculations of electron multiplication above breakdown. Results are shown to be in agreement with measured values at low currents and gas pressures above 30 Torr.

The theory and design of a low temperature coefficient, hemispherical geometry corona tube is presented. Modifications to the relevant voltage-current theory of coronas show improved agreement with measured characteristics. A qualitative explanation of the temperature coefficient is given.

The values of D/μ (diffusion/mobility), α/p (ionization) and η/p (attachment) have been determined simultaneously using Huxley's technique over the range 40<E/p<110 V cm⁻¹ Torr⁻¹ in CF₄ and the range 90<E/p<210 in C₂F₆, C₃F₈ and C₄F₁₀, with gas pressures in the range 0·6 to 2 Torr. Electron drift velocities have also been measured in these gases over the same E/p range by using a time-of-flight method. The η/p values in C₃F₈ and C₄F₁₀ are pressure dependent but the α/p values are not. This pressure dependence presumably arises from the collision-stabilization of the excited molecular ion C_nF_2n+2^−*. Similarly, the D/μ values also increase slightly with pressure. The measured α/p and η/p are in reasonable agreement with the earlier measurements. The drift velocities are independent of the gas pressure and indicate that the momentum transfer cross sections are similar in magnitude and energy dependence.

The interrupted vacuum arc is shown to be potentially useful as a general tool for the assignment of charge states to unclassified lines of at least moderate intensity. Photoelectric observations of lines of Th I, II, III and IV, interpreted with the aid of a simple model of ambipolar diffusion in a magnetic field, suggest that the intensity enhancement is quadratic in the field strength, and possibly also in the ionic charge number. The limitations to the usefulness of the source are provided by its inherently fluctuating signal and the fact that a larger degree of enhancement requires a lower intensity arc.

With a continuous electron beam, the spatial resolving power in the β-conductive method for semiconductors is governed by the diffusion or drift length for minority carriers, which depends upon the lifetime for minority carriers. The resolution should be improved with a pulsed electron beam, since an effective lifetime for minority carriers generated by the pulsed beam shortens as the beam frequency rises. Electric field intensity of 0·49 to 4·4 V cm⁻¹ in an n type germanium bar with a typical lifetime of 12 μs was measured at beam frequencies of 0·1 and 100 kHz to confirm the theoretical expectation. The energy, current and diameter of the beam were 15 keV, about 0·36 nA (RMS) and smaller than 1 μm, respectively.

The variation of the superconducting-to-normal transition field as a function of temperature is evaluated for superconductors having impurities which vary in density through a thin surface layer. Numerical results are obtained for tantalum, in which impurities cause the appearance of a tail to the M-H curve above H_c. The precise shape of the tail is also evaluated.

Measurements of the S-N transition and M-H curves of a tantalum sample impregnated with hydrogen are reported. Results are in excellent agreement with the theory of the preceding paper and show the effect on superconducting properties of an impure layer near the surface of an otherwise pure and strain-free sample. A profile of the impurity concentration near the surface is derived, as measured by the local value of κ.

The resinous substance oozing from the bark of the tree Vateria Indica is found to be a good thermoelectret material, with considerable remnant surface charges which remain hetero in nature throughout. A unique feature of this resin is that no charge reversal is observed, even when the polarizing field is about 40 kV. Near the melting temperature, this amorphous material is polarized by application of an electric field, even for the very short time of 30 min. The slower the rate of cooling, the greater is the charge retention observed. Even with no polarizing field, some moulding charges are observed, but these are small in magnitude and decay very quickly.

The calcium-vanadium garnet system Y_3-2x-aCa_2x Gd_aFe_5-x-z V_xIn_zO₁₂ is investigated as a function of x and a for an indium content given by z=0·25. Magnetic properties and resonance linewidth observations on polycrystalline samples are discussed. Selected materials from the range are compared with yttrium-gadolinium-aluminium-iron garnets with respect to magnetization characteristic and resonance linewidth; and it is concluded that the calcium-vanadium garnets are superior to the conventional system for xgreater, similar0·5, and at least while aless, similar1·2.

The water adsorption and voltage dependence of the surface conduction current at room temperature has been investigated at various relative humidities for quartz, Teflon and cellulose acetate. The results were analysed using the BET equation, so that the monolayer adsorption could be determined and the surface conductivity related to the number of water layers adsorbed. This showed that for Teflon, the surface of which has a weak attraction for water molecules, the conductivity increased exponentially with the number of sorbed layers of water. For quartz, for which the attraction is strong, the conductivity only commenced to increase exponentially after the completion of the first layer.

A technique is described which enables copper or silver (111) films grown epitaxially on mica to be removed from the substrate by means of a two-stage process involving the use of hydrochloric acid and then distilled water.

Silver grown epitaxially on the copper films so obtained gives rise to 11·1 Å Moiré fringes which are suitable for the calibration of an electron microscope.