Table of contents

A new microwave tube design, suitable for application in microwave ovens, is described. It is a development of the basic planar magnetron in which the cathode and anode are two annuli and the magnetic field is radial. Potential advantages over existing designs are: higher power density, higher efficiency, easier tuning, the probability of reduced harmonics, and lower manufacturing costs.

The depths of the peaks of damage distributions produced by implantation of 50-1100 keV ⁴He⁺ ions into Y-cut single-crystal LiNbO₃ have been determined using proton channelling. These values are about 20% lower than those deduced from optical measurements reported in the literature. This information is required for the design of integrated optical devices in LiNbO₃ produced by ⁴He⁺ ion implantation.

It is shown that recombination is likely to be less important than diffusion as a plasma electron and ion loss mechanism in a number of hollow cathode discharge tubes with long internal anodes and helium pressures of 5-30 Torr, with dimensions comparable with those used for some gas lasers, but that recombination may predominate in similar tubes with end anodes.

Measurements of DC electrical conductivity and ESR were made on 35TeO₂-(65-x)V₂O₅-xFe₂O₃(mol%) glasses. They suggest that when x is changed from 0 to 1, the conductivity increases due to a decrease in effective electron hopping distance between the transition metal ions. When x is increased to greater than unity, the conductivity decreases because hopping is inhibited due to formation of Fe-O-Fe and Fe-O and Fe-O-V bridge bonds. The conductivity has a distinct maximum at x=1.

The relative permittivity ( epsilon ') and loss ( epsilon ") have been measured for vinyl chloride-vinyl acetate-vinyl alcohol terpolymer in the frequency region 0.1-100 kHz and in the temperature range 77-410K. Two relaxations, a strong alpha and a feeble beta relaxation, have been observed. The activation energy for the alpha relaxation lies in the range 0.86 approximately 0.90 eV and it is attributed to the segmental motion of the main chain of the constituent groups of this terpolymer under dipole-dipole interaction in the amorphous region.

The open-tube diffusion of Sn in GaAs and Zn in InP and InGaAs from spin-on films acting both as solid diffusion sources and as surface passivators is reviewed. Technological processes are described which lead to layers with reproducible, homogeneous properties necessary for device applications. The diffusion models which quantitatively predict the diffusion results are discussed. Experimental results are given showing the influence of film composition, diffusion temperature and time, and substrate properties, on surface morphology, carrier concentration and concentration profile and on carrier mobility. Applications of the process to highly doped, low resistivity contact layers, highly doped p⁺ gate layers and n-doped FET channels are demonstrated. Finally the potential use of doping from spin-on film instead of or in addition to existing doping processes (e.g. ion implantation) is discussed. It is concluded that this process adds a further degree of flexibility to the technology of III-V semiconductor compounds.

The authors study confined propagation of slow (thermal) neutrons along (non-hollow) solid fibres made of certain elements (Ti, Mn, ...) such that amplitude for the low-energy nuclear scattering of neutrons on them be negative. Geometrical optics and quasiclassical descriptions, procedures for confining the neutrons, and some applications to radiotherapy are outlined. The confined propagation modes for slow neutrons along infinite homogeneous circular fibres without and with nuclear absorption are analysed. Some estimates of the spectral density in the neutron flux and its attenuation are outlined. In order to assess lattice periodicity effects, the potential seen by a neutron inside an infinite periodic solid fibre and its confined propagation are discussed in detail. Here the authors find wide allowed and small forbidden bands for the neutron energy along the periodic fibre: well inside the allowed bands the neutron propagation modes reduce, as a first approximation, to those for the homogeneous fibre. Lattice vibration effects and the penetration, confinement and eventual scattering of neutrons by a homogeneous fibre are also analysed.

The radial and axial forces on a solenoid are found with a new technique. The authors represent a solenoid by many circular filaments and the self inductance of each filament and the mutual inductances between each two filaments are calculated using Grover's tables. Then the energy is calculated by summing the mutual plus self inductive energies. The radial force is calculated by using the principle of virtual work in which an increase of one of the radii r_i, by dr_i changes the energy with respect to this change in r. The axial forces are calculated by the same technique, that is by increasing one of the axial distances z_i by dz_i and calculating the change in energy with respect to this change in z.

The propagation of radiation through an aerosol whose properties are changing with time due to coagulation and deposition has been studied. Using the Mie scattering law for a perfect reflector averaged over the Planck function and a realistic treatment of anisotropic scattering the authors have solved the equation of radiative transfer for the heat flux through a plane parallel atmosphere of aerosol. The aerosol size distribution is obtained as a function of time from the kinetic equation of coagulation using a simplified Brownian coagulation process. Results show that the heat flux through the aerosol depends sensitively on the initial size of the aerosol particles and can pass through a minimum before ultimately reaching its free streaming value as the aerosol eventually disappears. The importance of accounting for the anisotropy of scattering of the radiation by the aerosol particles cannot be over emphasised.

Experimental apparatus is described to detect EPR in solids using a low temperature version of the photo-acoustic effect involving second sound in superfluid helium. By chopping the microwave power to the sample second sound is generated and amplified by resonance in a chamber maintained at constant temperature. The process is analysed and is shown to provide the same depth profiling capability as the normal photo-acoustic effect. Some results are presented to provide illustration and comparison with other techniques.

A laser-Doppler anemometer was used to measure the radial variation of axial turbulent velocity in the flow of water and aqueous polymer solution through a round pipe. Results were obtained for the mean velocity the turbulent intensity, and the one-dimensional energy spectrum. The polymers used were polyacrylamide (Separan AP 273; in a concentration range 25-200 WPPM). Both polymers are well known as effective additives to reduce turbulent drag, when dissolved in water to give a solution concentration of a few PPM. The mean velocity and turbulent intensity were both found to be increased by the polymer additives, with the magnitude of the effect depending on the polymer concentration This was in agreement with the results of other investigations. At low additive concentrations, the energy spectra were found to be identical to those for water flows; this also was in agreement with previous results. At higher concentrations, energy spectra showed noticeable attenuation in the largest (dissipation) range of wavenumbers. There was a corresponding enhancement of the small-wavenumber (energy-containing) range. This seemed to be a threshold effect with onset at a concentration of between 50 PPM and 100 PPM for Polyox WSR 301 and between 25 PPM and 50 PPM for Separan AP 273.

Discusses the relationships between the surface composition and the mechanical properties of carbon steels implanted with nitrogen. Conversion electron and X-ray Mossbauer spectroscopy (CEMS and CXMS) were used to investigate the surface modifications of the implanted samples. Thermal annealing was performed in high vacuum, at temperatures between 250 and 500 degrees C, in order to simulate the temperature increase in real tribological processes. It is shown that the improved performance of nitrogen-implanted carbon steels against wear and fatigue is mainly due to the action of finely dispersed iron carbonitrides ( theta - and epsilon -Fe₃(C,N)). It is shown also that the persistence of the protective action at greater depths is associated with the in-diffusion of nitrogen released by thermal decomposition of the compounds formed at the surface.

The changes in the thermally stimulated current (TSC) response of polyethylene to 200 rad of X-rays or neutrons are investigated after the exposure of specimens to a large dose of the respective radiation. This was done in order to assess possible changes in the trap concentration of the specimens. It is shown that both X-rays and neutrons can create additional traps in polyethylene at a rate dependent on the amount, and possibly fractionation, of the doses used. The results indicate a higher trap creation rate for low doses as compared with high doses, within the dose ranges used.

The permittivity of BaTiO₃ doped with small concentrations of Gd₂O₃ (0.01 approximately 0.1 mol.%) are found to be remarkably dependent on the type of the solid solution formed between Gd₂O₃ and BaTiO₃. The decrease of permittivity at the Curie peak with decreasing grain size for BaTiO₃ doped with concentrations of Gd₂O₃ from 0.5 approximately 3 mol.% is attributed to the formation of defective non-ferroelectric grain boundary layers of low permittivity.

The wavelength and temperature dependence of the Faraday rotation together with the optical loss spectra of yttrium, gadolinium, terbium, dysprosium, holmium, erbium and ytterbium iron garnets are reported for wavelengths in the range 1.1-1.7 mu m. It is demonstrated that the Faraday rotation of all the iron garnets decreases with increasing wavelength with the exception of ytterbium iron garnet which, for wavelengths in excess of approximately 1.3 mu m, possesses a wavelength independent Faraday rotation of 5.7+or-0.3 degrees mm^-1. The performance of magneto-optic switches, isolators, modulators and deflectors constructed using each of these materials is discussed with particular emphasis on their operation at 1.3 mu m and 1.55 mu m, the wavelengths of interest in current optical fibre systems. It is concluded that whilst yttrium iron garnet or holmium iron garnet are best suited to the fabrication of devices operating at single wavelength, for broadband operation ytterbium iron garnet is to be preferred.

Electroluminescence (DC and AC) and photoluminescence of CaS:Cu, Er and CaS:Cu have been investigated. Emission spectra have been explained on the basis of the Williams-Prener model. The brightness-voltage dependence satisfies the relation B=B₀ exp(-b/V¹2/) though in some cases two modes of variation are effective. The temperature dependence of PL brightness does not show any appreciable change while that of EL brightness shows a number of peaks. The EL efficiency passes through a maximum at some intermediate value of voltage. This is explained in terms of a transport process of the Schottky-emission type.

An ion source capable of generating ions from a wide range of normally solid materials is described. The source operates by focusing a powerful electron beam on to a molten target, the electrons serving to both vaporise and ionise atoms of the target. The ion beam drawn from the source possesses many desirable properties including a low energy spread, very high purity and high brightness.

The chemical composition of a large number of transmission mode S1 photocathodes, prepared by a standard process in situ in an ESCA spectrometer has been examined using XPS. In particular the stoichiometry of the caesium oxide layer has been determined at the different stages of cathode formation. The method involves the measurement of XPS peak areas and the use of Schofield's values for the sub-shell photoionisation cross-sections. The silver content of the cathode oxide occurs. Thus the XPS peak area measurements and not the oxygen 1s peak position must be used to determine the stoichiometry of the caesium oxide. The cathodes with the highest photosensitivity and greatest stability were found to have a caesium-to-oxygen ratio very close to 2:1. The results are therefore not consistent with suggestions that the caesium suboxide Cs_IIO₃ is an important constituent of the S1 photocathode. In support of the XPS results the authors measured the photoresponse at different wavelengths from 555 nm to 1.1 mu m and photoelectron energy distribution curves from which the work-functions of the cathodes are obtained.