Table of contents

The flow of a Walters' liquid past an infinite plate is considered, when there is a constant heat flux between fluid and plate, and taking into account the influence of the viscoelastic fluid on the energy equation.

O₅^-ions have been detected and measured in a positive column of glow discharge in oxygen between 0.04 and 0.17 Torr. A suitable ion-molecule reaction has been proposed, which appears to be supported by the mass spectrometer measurements.

It is observed that in addition to the macroscopic hollow-cathode effect between two parallel mesh electrodes, microscopic hollow cathodes are formed in the holes of the wire mesh. With a mesh hollow cathode as a plasma source, a cylindrical plasma with a charge density of the order of 10⁸ cm^-3 is obtained.

The effect of a surface space charge exhaustion and inversion layer on the Hall and thermoelectric properties in a non-degenerate semiconductor film has been examined theoretically. An experimental approach is indicated for the determination of surface potential and the ratio of surface to bulk conductivity.

A new open-flow vapour phase process is reported for the epitaxial growth of cadmium mercury telluride on to substrates of cadmium telluride. The layers have been characterised by in-depth profiling using secondary ion mass spectrometry and also the electrical properties have been assessed using the van der Pauw technique. Material with x values in Cd_xHg_1-xTe ranging from 0 to 0.5 have been grown at approximately 410 degrees C.

For pt.I see ibid., vol.13, p.1811, 1980. A recently developed method, which reduces a particle transfer problem in finite plane-parallel media to a problem of a semi-infinite media by means of invariant embedding is used to find the reflection and transmission functions of the finite medium, assuming that the surface of the medium is subjected to an angular flux of the type psi (0, mu )= mu ^beta mu >0 beta =0,1,2, ... Calculations for the semi-infinite slab show that the Eddington approximation (the diffusion-type model) used here is adequately accurate for thick slabs. When applied to finite slabs with beta =0, the accuracy is within 1% for slabs thicker than one mean free path. When applied for beta >0, accuracy of better than 1% is achieved in slabs of only one mean free path. The same approach is applied to a synthetic kernel approximating the two-term Henyey-Greenstein phase function. The modelled scattering law allows a combination of forward scattering, back scattering and linearly anisotropic scattering.

Measurements at 3 GHz of the microwave properties of a superconducting thin-film microbridge coupled to a narrowly tuned strip-line resonator (coupled Q approximately 10³) indicate that such a device displays the same variations in small-signal impedance as predicted by the resistively shunted junction model of a Josephson weak-link. Whenever this impedance becomes negative the microbridge is found to generate microwave radiation whose frequency is determined not by the junction bias voltage but by the natural resonance of the strip-line.

It is shown that the stepwise excitation process from the Cd(II) ground state is the dominant one for the upper state of the 441.6 nm laser line in the positive column Ne-Cd⁺ laser discharge. The much smaller laser output power in Ne-Cd than that in He-Cd cannot be explained by the nonexistence of the Penning excitation process for the laser upper state in Ne-Cd. It is explained by the smaller stepwise excitation rate for the laser upper state in Ne-Cd than that in He-Cd and the influence of both the laser lower state density and the loss of the cavity.

Laser-induced fluorescence has been studied in high-pressure mercury, mercury-metal halide and sodium-mercury arcs, using a rhodamine 6G CW dye laser for the excitation. The fluorescence was observed at 90 degrees with respect to the laser beam. The fluorescence is interpreted assuming thermal equilibrium in the excited region of the arc. Quantitative evaluation of the fluorescence from the mercury arc indicates the validity of this approach. Laser-induced fluorescence can be used to determine local density ratios of arc plasma components and local emission profiles (line shapes and line shifts). As an application the electron density and the Na-Hg density ratio at the arc axis of a sodium-mercury discharge are determined from Stark shifts in the fluorescence of several transitions in the sodium atom and from fluorescence intensities.

Positive ions formed by spark discharges and via reactions following the discharge in SF₆ in the pressure range 13-67 kPa have been detected and identified using high-pressure quadrupole mass spectrometry. Results are presented for ions produced in 'unpurified' SF₆, 'purified' SF₆ and binary mixtures of 'purified' SF₆ with N₂ and O₂. Without reduction of air and water impurities to the parts per million level the major ions detected at P>or approximately=40 kPa were N₂O₂F⁺, H₂SOF₂⁺, N₂F₄⁺, S₂NF₄⁺, S₂NOF₄⁺, S₂NO₂F₄⁺, and S₂NF₈⁺. These were identified through additions of N₂, O₂, D₂O, and the measurement of sulphur isotope ratios. After extensive purification of SF₆, the predominant ions at these pressures were S₂F₇⁺ and SF₃⁺. The effect of impurities is discussed in light of work performed by others which shows that the long-lived neutral products depend strongly on impurities.

A method is proposed which uses the observed nonlinearity in the short-circuit current versus light intensity curve at high intensities, to determine the series resistance of solar cells.

Surface composition and depth profile studies of chemiplated thin film CdS:Cu₂S solar cells have been carried out using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. These studies indicate that the junction is fairly diffused in the as-prepared cell. However, heat treatment of the cell at 210 degrees C in air relatively sharpens the junction and improves the cell performance. Using the Cu(2p₃2/)/S(2p) ratio as well as the Cu(LVV)/(LMM) Auger intensity ratio, it can be inferred that the nominal valency of copper in the layers above the junction is Cu⁺ and it is essentially in the Cu₂S form. Copper signals are observed from layers deep down in the cell. These seem to appear mostly from the grain boundary region. From the observed concentration of Cd, Cu and S in these deeper layers and the Cu(LVV)/(LMM) ratio it appears that the signals from copper essentially originate partly from copper in CuS and partly from Cu²⁺ trapped in the lattice. It is significant to note that the nominal valence state of copper changes rather abruptly from Cu⁺ to Cu²⁺ across the junction.

Time lags to breakdown in n-hexane have been measured at pressures up to 10 kg cm^-2, using a rectangular pulse generator of 100 ns duration. The measurements have been also carried out on the liquid contaminated by gaseous impurities, Ar, N₂, O₂, and CO₂. The lags for Ar or N₂ contamination at 5 kg cm^-2 are equally distributed with that for the air-saturated liquid at atmospheric pressure. However, for O₂ or CO₂ contamination, the distributions of time lags are drastically changed from the B to N type. The results can be successfully explained by the electron avalanche model of breakdown.

The persistent electrical polarisation in polyvinyl butyral was investigated by measuring the thermally stimulated discharge (TSD) current at different polarising fields, temperatures and heating rates. A peak was observed at about 331K which has the characteristics of a dipolar relaxation process. Thermal sampling technique showed that the relaxation is distributed. Differential thermal analysis gave a second-order transition at about 334K. Because of the good correlation between both thermal techniques it is concluded that the TSD peak is associated with the glass transition of the polymer, and therefore it involves the motion of large parts (sequences of 20-50 carbon atoms) of the polymer chains.

Temperature-dependent currents have been observed in unpolarised samples of poly(vinyl alcohol) heated at a constant rate in short circuit. The position of the current peak in the thermal spectrum shifts with the heating rate, and its magnitude depends on the electrode material used. The activation energy of the process responsible for the current has been determined. The possible origin of the spontaneously generated current is discussed.

Most of the existing methods for obtaining frequency factors make use of the trap depth, or make some assumption regarding the order of kinetics. This introduces arbitration, as the E values obtained using various methods differ appreciably. This is one of the reasons for the inconsistencies in the reported trapping parameters. A method independent of trap depth is needed. Such a method, making use of the isothermal decay of TL, is presented.

A new model is proposed for explaining the nonlinearity in the response characteristics of three common thermoluminescent phosphors (CaSO₄:Dy, CaF₂:Dy and Mg₂SiO₄:Tb). The increased trapping of charge carriers in the dosimetry traps during irradiation, due to a reduction in trapping efficiency of deep traps caused by radiation damage, was found responsible for the supralinearity in TL response of dosimetry peaks and sublinearity in TL response of high temperature peaks of these phosphors at high gamma ray doses. The dose versus TL response characteristics of deep traps in CaSO₄:Dy was found to vary drastically from batch to batch, and in CaSO₄:Dy, the sensitisation observed after a gamma ray dose of 10³ Gy and annealing at 400 degrees C was found useful in low dose measurements.

Reports measurements of electron emission yields of clean molybdenum surfaces under bombardment with H⁺, H₂⁺, D⁺, D₂⁺, He⁺, N⁺, N₂⁺, O⁺, O₂⁺, Ne⁺, Ar⁺, Kr⁺ and Xe⁺ in the wide energy range 0.7-60.2 keV. The clean surfaces were produced by inert gas sputtering under ultrahigh vacuum. The results were compared with those predicted by a core-level excitation model. The disagreement found when using correct values for the energy levels of Mo is traced to wrong assumptions in the model. A substantially improved agreement with experiment is obtained using a model in which electron emission results from the excitation of valence electrons from the target by the projectiles and fast recoiling target atoms.

The mass loss of the anode of a positive-Ga-ion source is determined from microbalance measurements, when the source is operated in a steady state. The anode consists of a short W point electrode covered by a film of liquid Ga kept at 6-9 kV with respect to an earthed cathode. From spectrograms of the light emitted by this ion source it is known that neutral Ga atoms are produced during operation, besides fast positive ions. The rate of the mass loss of the emitting Ga-covered needle is found to rise approximately linearly with the current, i.e. the mass of Ga emitted per unit charge is constant, provided the current does not exceed 100 mu A. At larger currents the mass loss rate rises faster than the current. The nature of the emission of neutral atoms is briefly discussed. It is concluded that thermally activated, classical atomic evaporation cannot be the primary mechanism responsible for the neutral component of the emission.