Table of contents

A series of experiments have been carried out to try and detect 'cold fusion' in titanium which has been loaded with deuterium at high pressure. No neutrons were detected using a range of counting systems, the most sensitive of which could detect 0.9 neutrons/s if sustained over 100 s. Bursts of more than 30 neutrons occurring in a period of less than 0.1 s could also have been detected using coincidence counting. Evidence for erratic behaviour of proportional counters, which could be mistaken for neutron emission, is presented.

A versatile nuclear track technique has been employed to measure energy loss and mean ranges of 18.04 MeV/u ⁹³Nb ions in nickel and tantalum. A polyallyldiglycol carbonate (CR-39) track detector has been calibrated and used in the present work to determine the energy of the transmitted heavy ions through metal targets. The passage of ⁹³Nb in nickel and tantalum was studied in terms of energy-loss rate and mean ranges. The experimental values are also used to check the validity of theoretical data obtained from a few commonly used theories and data tables. The experimental technique is also briefly discussed.

The fields radiated into free space by a point electric dipole embedded at the centre of a chiral sphere are obtained and discussed. It is shown that embedding in a chiral sphere enhances the radiation resistance; in addition, from the point of view of an observer in free space, the point electric dipole embedded in a chiral sphere appears to be made up of a point electric dipole and a point magnetic dipole. These observations indicate the potential use of chiral materials for making antenna radomes.

A model of the thermoelectric eddy currents occurring in the electron beam and laser welding of two dissimilar metals is presented, based on irreversible thermodynamics. The distribution of eddy currents and the magnetic field generated are computed and the resulting deflection of the electron beam is calculated, approximately. The model predicts large thermoelectric currents in the workpiece and a deflection of the electron beam that is in good agreement with experiment.

Multiple-beam Fizeau fringes in transmission have been applied to investigate the optical dispersion properties of blue Cashmeline fibres. The refractive indices were determined at different wavelengths for light vibrating parallel and perpendicular to the fibre axis. It was observed that both n/sub /// and n_{perpendicular to} follow Cauchy's dispersion relation over the visible range of the spectrum. The constants A and B of Cauchy's formula were estimated. The observed results were interpreted in terms of the axial symmetry of the fibre.

The plasma parameters in noble-gas narrow-tube and capillary-tube plasmas have been studied experimentally over the pressure (p) range from 0.1 to 10 Torr. Tube inner diameters, 2R, of 0.5 and 0.8 mm (capillary) and 3 mm (narrow) were used in the present investigation, together with axially movable anodes and cylindrical electrostatic double probes for the electric field and the electron temperature measurements, respectively, in noble gases, i.e. He, Ne, Ar, Kr and Xe. The results show that the axial electric field E_z/p and plasma density decrease with increasing pR and the atomic weight of noble gases. No significant tube radius effect has been observed for the axial electric field if one analyses results in terms of pR. The electron temperature decreases significantly with increasing pR for He and Ne, and depends slightly on pR for Ar, Xe, and Kr.

A non-perturbing probe for drift velocities in high-density plasma flows is described. Coherent Thomson scattering has been used for direct and local measurements. Two pulsed laser beams probe the plasma flow alternately from two different directions yielding measurable Doppler shifts. The high repetition frequency of the laser system permits the detection of small relative Doppler shifts of the scattered light pulses by means of a correlation technique. The influence of fluctuations of the scattered light intensity is eliminated by employing two detection units with different spectral characteristics. Local values of drift velocities and electron densities can be measured simultaneously at particular points in the plasma flow. Drift velocities between 0.3 and 2.7 km s^-1 and electron densities between 10²² and 10²³ m^-3, depending on the discharge conditions of the plasma thruster (current, gas composition), are found. The laser Doppler technique presented provides a spatial resolution better than 1 mm³.

Electrothermal instabilities occurring in the near-electrode regions can cause breakdown in the slag layer as well as in the adjacent plasma electrostatic sheath and can lead to arcing. The breakdown process can occur either from the slag layer or from the plasma sheath, depending on the electrode temperature and the slag electrical conductivity. Stability analysis has been carried out for the onset of instability at the cathode, using a perturbation approach both in the slag layer and in the adjoining plasma boundary layer. The critical current densities and the critical voltage drops for breakdown of both the slag layer and the plasma sheath have been calculated and the region of instability initiation has been identified. The initiation of instability has been found to be a function of electrode, slag and plasma parameters. It was also found that the constricted discharge can be limited to occur either in the slag layer or in the plasma sheath alone or it may occur in both layers.

The experimental analysis of the variation of the neutral molecule density induced by the first corona in a 2 cm point-plane pulsed discharge in air (2-9.5 bar) and SF₆ (560 Torr-2 bar) is performed by a new diffracted schlieren technique (schlieren device associated to a photomultiplier). Two time constants-the time lag and the recovery time-have been measured in the vicinity of the point electrode where the neutral depopulation mechanism first appears and is maximum. The time lag represents the inertia time of the gas to the energy injected, that is to say the time between the energy injection and the beginning of the variation of the neutral density in the core of the discharge. In air for these experimental conditions, the time lag is invariable and equal to 60+or-5 ns. The recovery time is the delay for the neutral-gas density perturbed by the first corona to get back to its initial density. Irrespective of which gas is used, the recovery time is of course a function of the injected energy, but also a strongly decreasing function of the duration of the HV pulse.

For pt.II see ibid., vol.22, p.632 (1989). The extensive collisional-radiative model for an argon atom plasma is applied to atmospheric and subatmospheric pressure wall-stabilised arcs in order to clarify the mechanisms by which the excited levels are populated in the axial region of these discharges. Computations are carried out for various sets of input parameters, such as the electron kinetic temperature T_e, the atom temperature T_a, the ion temperature T_i, the electron number density n_e, the ground-state atom population n₁, the plasma column radius R and the escape factors Lambda _mn and Lambda _m, characterising the non-equilibrium plasmas under consideration. The predicted values of the populations in the excited levels and the qualities derived from them, as well as the values of the critical electron densities for establishing the local thermodynamic equilibrium in the axial region of the arcs investigated, are in good agreement with the corresponding experimental results. The effect of the changes in the discharge parameters T_e, T_a, n_e, R and Lambda _1n on the population mechanism, together with the role played by the recombination flow of electrons from a continuum, the deviations of the actual electron distribution function from the corresponding Maxwellian form and by the atom-atom inelastic collisions, are also shown.

The operation of the SF₆ puffer circuit breaker relies on he pressurisation of gas by a combination of piston compression, nozzle blocking and gas heating. Theoretical modelling of the physical processes occurring during high-current interruption is important for mechanical design and for prediction of electrical performance. A high-current arc model has been developed, which takes account of observed gas behaviour throughout the arcing period and beyond current zero. The predicted pressurisation is compared with experimental work, and shows good agreement over a wide range of operating conditions. The theoretical model pays particular attention to the mechanisms of heat transfer within the upstream region of the interrupter, and incorporates a new description of the arc thermal boundary.

A point-plane corona discharge in ambient air is modelled by regarding the drift of ions from the coronating point-electrode to the earthed plane as a succession of non-interacting uniform spheres of charge. Each sphere is thought to expand in its self-field as it drifts in the mean field between point and plane. The space charge deposited by the spheres on their arrival at the plane implies a current distribution which gives an analytic alternative to Warburg's empirical expression. It is shown that the parameters of the model can be adjusted to give a good fit to experimentally obtained results for negative coronas. The success of this simple model is discussed in terms of experimental observations and recent theoretical developments.

Thermal and mechanical properties of photoreceptor-type amorphous selenium (a-Se) films have been studied via differential scanning calorimetry (DSC), thermomechanical analysis (TMA) as well as thermomicrohardness analysis (T mu HA). The a-Se films were vacuum deposited by thermal evaporation onto heated Al substrates and identically aged. The experiments were carried out over a temperature range encompassing the glass transformation to examine the nature of physical processes controlling the thermal and mechanical properties. In DSC experiments, the glass transformation kinetics was investigated via both heating and cooling schedules. By applying the present thermoanalytical methods-Ritland and Kissinger analyses-it proved possible to identify a typical Vogel-Tammann-Fulcher ( approximately exp(A/(T-T₀))) type of response in the structural retardation times controlling the relaxation of the enthalpy. It was found that over a common temperature range, the temperature dependence of the mean relaxation time tau (T), whether determined from heating or cooling schedules, followed the viscosity-temperature data for a-Se suggesting that tau (T) approximately eta (T). The temperature dependence of the microhardness, H_v(T), on a semilogarithmic plot evinced a sharp decrease at a temperature T_g in the glass transformation region. The origin of this sharp decrease in the microhardness has been attributed to a structural relaxation process which has a mean retardation time proportional to the viscosity as in the enthalpy relaxation process. In the case of TMA however, it was found that the shift in the softening temperature with the heating rate indicated an apparent activation energy less than that for the viscosity. Two possible models are discussed for the interpretation of the TMA softening temperature which are based on the relaxation of the elastic modulus and an elastic deformation to viscous flow transition. By comparing the results from the present thermal and mechanical studies with the reported viscosity-temperature data, it is concluded that the rate of relaxation of enthalpy and microhardness of a-Se in the glass transformation region is inversely proportional to the melt viscosity which can be adequately described over a temperature range above approximately 30 degrees C by a Vogel-Tammann-Fulcher expression.

An attempt has been made to find out precisely the errors involved in the determination of the activation energy (E) of a thermoluminescence (TL) peak by using the different variants of method of various heating rates, namely, those due to Hoogenstraaten (1958), Chen and Winer (1970), and Dussel and Bube (1967). It has been found that for all practical purposes the Chen-Winer and Hoogenstraaten methods can be considered to be independent of the order of kinetics of the TL process. Finally, the applicability of the findings has been tested experimentally by considering a non-first-order TL peak. The results suggest that the theoretical errors in all the cases are less than the experimental ones and hence these methods can be safely used for all types of TL peaks irrespective of their order of kinetics.

The preparation and properties of K₂Ca₂(SO₄)₃ doped with Eu are described. The phosphor is five times more sensitive than CaSO₄:Dy. It has a linear response, simple glow curve, emission peaking at 415 nm, negligible fading and excellent reusability. It is claimed that this phosphor can replace CaSO₄:Dy.

This paper presents results obtained in a detailed study of the changes induced in TLD-100 glow peaks IV and V, during storage at 45 degrees C for up to 10 days. The modifications exhibited by the glow curve have been studied using a computer fitting programme to resolve the individual peak components. While peak V only experiences an increase in the number of traps, peak IV suffers marked modifications in position, intensity and width, revealing important changes in the trap structure, affecting to a different extent empty or filled traps. No evidence for loss of TL signal due to leakage of trapped charges has been found for peaks IV and V, during storage at 45 degrees C.

The authors have examined the electrical properties of ultrathin insulating layers of polyimide (PI) deposited on a base of Au electrodes by using tunnel junctions with structures of Au/PI/(Pb-Bi) and Au/PI/Au. For Au/PI/Au junctions, ultrathin PI Langmuir-Blodgett films having good electrical insulating properties were obtained when the number of deposited layers was greater than about 30. It was found that the I-V characteristic of electrically insulating Au/PI/Au junctions was explained by a model on Simmons' tunnelling theory (1963), assuming that application of the top Au electrode resulted in a reduction of the PI layer thickness. For Au/Pi/(Pb-Bi) junctions, typical I-V characteristics of tunnel junctions were obtained at a temperature below the critical temperature of a superconducting Pb-Bi alloy, when the number of deposited layers was 27. It was concluded that the I-V characteristic was governed by the tunnelling conduction mechanism based on the Bardeen-Cooper-Schrieffer (BCS) theory.

Thin film p-cadmium telluride that has been electrodeposited from non-aqueous propylene carbonate has been doped with copper using two electrochemical methods. The first involved electrochemical codeposition (in situ doping) of copper and cadmium telluride, and the second employed electromigration of copper into thin film cadmium telluride that had been annealed. After the film was removed from the conductive substrate, the resistivity of the resultant film was determined by either two- or four-strip methods, depending on the resistance of the film. To avoid current leakage by way of surface moisture, the film resistivity was measured under vacuum. The temperature dependence of the resistivity was determined for both doped and undoped films, and activation energies were obtained. As the copper density was increased, the resistivity and activation energy decreased. A Hall effect measurement of highly doped film revealed that the carrier density is substantially less than the estimated copper density, indicating segregation of part of the copper into grain boundaries of the polycrystalline film. Similar behaviour has been observed for other polycrystalline thin films. The effect of copper density and mobility are affected by grain boundary states.

The optical response of a system consisting of a small dielectric sphere containing a smaller eccentrically embedded sphere of different dielectric properties is investigated. By employing bispherical coordinates the problem is reduced to the solution of a system of linear equations. The results of numerical calculations are presented illustrating the dependence of the infrared absorption spectrum of a CdTe-CdO system on the degree of eccentricity.

The authors describe a model of the indication-formation process in the magnetic particle inspection method of non-destructive testing. Optical microscopy is used to study velocities of individual suspended aggregates in known magnetic field gradients in order to test the validity of the model. Qualitative agreement between experimental and theoretical velocities is obtained although the presence of voids in particle aggregates prevents a quantitative comparison. The effects of magnetising field, magnetic ink carrier coefficient of viscosity, defect aspect ratio and contrast paint layer thickness are studied by computer simulation using the model. Results suggest that optimum indication contrast in real systems should be obtained for carrier coefficients of viscosity in the region of 0.5 mPa s. Approximate agreement with the recommendations of the British Standard is found in the effect of the thickness of the contrast paint layer.

The authors study the arrangement of cells in undifferentiated vegetable tissues of five different species. The distribution of the number of sides, the average area (a_n), perimeter (p_n) and side length (l_n) of n-sided cells are determined as well as the correlation between the number of sides of a cell and of its neighbours. The results show that vegetable cellular nets obey Aboav-Weaire's law. They also discuss Lewis' law and a possible relation between (p_n) and n. The analysis of these structures provides a different example of random cellular structures and helps to show general aspects of the ideal one.

This paper presents the results of an investigation into the machining of single crystal silicon using miniature diamond cutting wheels. To achieve high surface velocities and a large dynamic stiffness, cutting pins are rotated at a speed of between 90000 and 100000 RPM using a commercial air turbine spindle. It is shown that surface degradation due to the grinding process is related to the dynamics of the process and, more importantly, to the geometry of the specimen/cutter interface. The surfaces generated by this process have been assessed using optical microscopy, etching, X-ray diffractometry, stylus techniques and scanning electron microscopy. This analysis provides further indications that the as-machined surface consists of an outer layer of submicrometre thickness that is under a high compressive stress. This is followed by a highly distorted and/or fractured layer that extends with decaying intensity into the bulk material.

Glass ion exchange is an attractive method for the fabrication of integrated optical components. In this article the possibility of making a single mode glass ion exchanged interferometer specially designed for stabilisation of a laser diode (LD) is investigated. The design of the interferometer was deduced from the temperature and injection current dependence on the wavelength of the GaAlAs LD emitting at 780 nm. The optical guide is fabricated on B-270 glass using a potassium-sodium double ion exchange process.

Sound velocity measurement have been made on sintered aluminium powder (SAP) compacts in the density range 1400-2400 kg m^-3. The sound velocity, and hence the acoustic impedance, is noticeably reduced in the lower-density compacts suggesting they may have some application as quarter-wave acoustic couplers.

This communication reports the time-of-flight simulation of electron drift velocity, in SF₆ together with the longitudinal diffusion coefficient in the E/P range of 80<or=E/P<or=220 V cm^-1 Torr^-1. The simulation results compared with recent measurements indicate the validity of the cross section set previously employed.

Cross sections of RF sputtered MoS₂ thin films are investigated using lattice resolution transmission electron microscopy and electron diffraction. The results are compared with X-ray diffraction measurements. The films have a (001) texture (type II) in the first nanometres near the interface and a conventional (100) texture (type I) in the upper part.

Samples of polyaniline (PANi) have been prepared electrochemically and oxidised to various oxidation states. These 'as-prepared' samples were investigated using ESR spectroscopy. It was found that both linewidth and g value are dependent on oxidation level. In the reduced form of PANi the spin species are ascribed to neutral pi -radical defects, indicative of spins trapped at chemical defect sites along the polymer chain. On oxidation to the 'emeraldine' form of PANi the g value is seen to shift. Such shifts in g imply that the spins which are injected during electrochemical oxidation reside on the nitrogen sites along the PANi chain. These spin species are different from those which are seen in the reduced form. Further oxidation of the emeraldine form cause a loss of nitrogen site spins, although at the highest oxidation levels studied (0.8 V against a saturated calomel reference (SCE)) such spins are seen to return. This could either be due to further spin injection on nitrogen sites during oxidation or the creation of spins at chain degradation sites, which are associated with nitrogen atoms, i.e. due to chain cleavage at ring-nitrogen bonds during hydrolysis.