Table of contents

The Monte Carlo model for electron scattering described in an earlier paper has been used to calculate the absorption and back-scattering corrections met in electron-probe x-ray microanalysis. Although agreement with experimental data is on the whole good, the calculated values for the correction factors are not sufficiently accurate for general use. However, in the case of light element analysis where very high absorption corrections are needed, the corrections calculated from Monte Carlo data are the best available at present. Values for the back-scattering correction factor R calculated for incident beam angles 22·5° and 45° to the normal surface are given.

The number of ionizations on a given j shell in any electron-bombarded target has been calculated analytically by means of the Bethe formulae. A general formula for the atomic number correction has been derived in the form of an equation using parameters that are functions of target composition and accelerating voltage. This equation allows the calculation of the penetration effect to be readily carried out. The electron range, in terms of beam energy, has also been calculated. Finally, it is shown that the correction is different in the case of thin-target analysis.

Experimentally determined mass absorption coefficients for various wavelengths from 0·5 to 10 Å in Al, Ti, Ni, Cu, Zr, Nb, Pd, Ag, Ta and Au are presented in tabular form; an accuracy to about ±1% is claimed. The tables contain both new and revised data which are compared with values published by Heinrich in 1966; there is good agreement between the two sets.

Measurement at microwave frequencies of electro-optic constants in optically active media involves a complex index-matching procedure in which both the difference between the microwave phase velocity and optical propagation velocity, and the dispersion of the plane of polarization of contributions to the optical modulation from different sections of the material must be taken into account.

A method of measuring the coefficient r₁₁ in crystalline quartz at 9 GHz is described and it is shown that the result is r₁₁=1·7 × 10⁻¹³ m v⁻¹, close to the value predicted by Cady from measured values of the d.c. coefficient and the piezoelectric constants.

A description is given of experiments carried out using pulsed ruby and argon lasers to investigate the possibility of producing pulses of high electron emission current densities from tantalum, tungsten and lanthanum hexaboride cathodes heated by a focused laser beam. Current densities as high as 10⁴ A cm⁻² were recorded using the ruby laser but subsequently it was shown, using the repetitively pulsed argon laser, that electron current densities of this order were obtained only when the cathode material was being melted. Lanthanum hexaboride was found to undergo changes on the surface when repetitively pulsed and was rejected in favour of the pure metals tungsten and tantalum. From these metals stable emission currents up to 1 mA peak were recorded from spots approximately 15 μm in diameter (i.e. 570 A cm⁻²) for several hours without incurring surface damage. Current density values of this order are near to those calculated from the Richardson equation for temperatures just below their melting points.

Experimental results have confirmed theoretical predictions regarding the delayed onset of emission, the delay in the peak emission relative to the peak light intensity and the extremely rapid termination of the emission pulse.

Measurements have been made of the spectral response of Cu₂S-CdS photovoltaic cells, prepared by the chemiplating technique, as a function of the plating solution concentration and the plating time. The results are interpreted qualitatively in terms of simple energy band theory and the resulting model compared with those already proposed.

The characteristics of an ammonia maser operated with a molecular beam which passes through two resonator cavities in succession are discussed. Experimental observations on the oscillation amplitude in the second cavity as a function of tuning of the cavities, separator voltage and beam flux are given in detail and related to previous work; some discrepancies are noted.

Measurements of the transmission spectra of thick silicon monoxide films are reported, and from these the absorption coefficient of silicon monoxide is calculated as a function of wavelength. The results obtained are compared with the predictions of a simple theoretical model.

The optical and magneto-optical properties of polycrystalline spinel ferrites and single-crystal rare-earth iron garnets have been determined at a wavelength of 337 μm using a HCN gas maser source. The relative performance of these materials as Faraday rotators in the far infra-red is discussed and the observed rotations are compared with theoretical predictions.

Measurements are given of the field gradient characteristics for arcs operating in tubes of different diameters in nitrogen. The recoveries of conductance for these tubes (diameters 4, 5 and 7 mm) are also given over a period of 300 μs following rapid interruption (1 μs). The arc behaviour under imposed gas flow conditions of 0-2·5 1. min⁻¹ is also described. In particular it is found that the recovery, when presented as a log conductance against time plot, has three linear regions. Time constants derived from these linear portions do not seem to exhibit a simple dependence on the confining tube radius and are at variance with previous theories.

A solution of the energy balance equation is also given, for conditions of variable thermal diffusivity combined with a non-linear relationship between the electrical conductivity and heat potential functions, and this gives close agreement with the experimental data.

The ratio of the electron diffusion coefficient to the mobility (D/μ), which characterizes the mean energy of the particles, has been measured in nitrogen and hydrogen over the range 7<E/p<40 v cm⁻¹ torr⁻¹ (20°C). A brief description of the apparatus and technique is included. The solution of the diffusion equation has been analysed to study the effects of the finite size of the electron source and the presence of walls.

Primary and secondary Townsend ionization coefficients, α and ω/α, were determined for nitrogen over the range 100<E/p₀<470 v cm⁻¹ torr⁻¹ from data on the spatial growth of currents in uniform fields. Values of α/p₀ were found to be smaller than those previously published for mercury-contaminated gas, the difference being particularly noticeable at higher values of E/p₀ and correspondingly lower pressures. Theoretical calculations of α, based on the Maxwellian distribution for electron energies, gave values comparable with those measured experimentally at E/p₀ similar 120 v cm⁻¹ torr⁻¹; calculations at higher electron energies would require large extrapolations of electron drift velocities and temperatures.

The observed variation of ω/α with E/p₀ can be explained quantitatively by assuming resonance neutralization of an ion to occur as it approaches the metal surface of the cathode; for sufficiently high approach velocities Auger de-excitation follows.

It is shown that the permanent high-pressure discharge which has not been observed hitherto in a uniform electric field can be established if the poor ion-bombardment effect is replaced by the more efficient Malter-Paetow effect. In such an arrangement the normal Townsend-like breakdown which, in most cases, develops into a streamer spark will be suppressed by the high resistance of an insulating film at the cathode surfaces. Owing to the symmetry of the system, the charge production by the Malter-Paetow effect at one electrode surface supplies enough charges to sustain the same process at the other electrode and vice versa. Experimental observations concerning the discharge behaviour as well as the variation of discharge current with pressure, electrode distance and applied voltage are reported. The drastic reduction of sparking potential between the two main electrodes due to the space charge is discussed.

The non-linear behaviour of the grid film encountered in electron tube blackout (grid film effect) has been investigated. The static (I, E) characteristics and the voltage dependences of the small-signal resistance and capacitance of the film are discussed, along with the methods of determining their values. The resistance was found to be 25 Ω or less, while the capacitance was in the 10-300 μF region. These various grid film properties were found to be approximately exponentially dependent upon the film voltage. A technique is given for calculating the decay of the grid film voltage with time. In addition, long-term electrical ageing of the films was investigated and typical curves are given. These include the result of a temporary cure of grid blackout by an extended period of grid current operation produced solely by cathode thermionic emission.

The problem formulated in the companion paper by Birss and Adamson (I) is solved numerically using an ICT 1905 digital computer. Solutions for the stress functions ψ and χ are obtained for a number of different axial ratios and the effect of varying Poisson's ratio is also investigated. A comparison is effected between numerical solutions and analytical expressions that may be derived for a sphere and for a prolate spheroid of large axial ratio.

Elastic constants are derived for composites consisting of fibres imperfectly aligned in an elastic matrix. The reduction in the axial Young's modulus is found as a function of angular fibre scatter for various values of fibre-matrix modulus ratio and fibre volume fraction. Applying this to resins reinforced with well-aligned whiskers it is concluded that the modulus reduction is of the order of 4% with respect to the perfectly aligned system.

Similar analyses are given for fibre arrays approaching a planar random mat and for arrays without axial symmetry.

The results of the variation of discharge current under pulsed illumination are presented, and their bearing on the underlying mechanism is pointed out.

Experimental values of the effective thermal conductivity obtained by Sugawara on calcareous sandstone partially filled with water are compared with values calculated by using the geometric mean equation of Lichteneker extended to a system having three phases and also with values obtained from a relation given by Brailsford and Major. The calculated values disagree with the experimental values. A weighted geometric mean of the maximum (weighted arithmetic mean of the individual thermal conductivities) and minimum (weighted harmonic mean of the individual thermal conductivities) values of the thermal conductivity of the sample is proposed here for obtaining its effective thermal conductivity. It is held that such an equation can demonstrate the structure and distribution of phases in the sample.