Table of contents

The effects of an electric field on the infrared spectra of materials can be studied using electrodes which are transparent to infrared radiation. The effects observed can yield information about the movement of molecular dipoles within the material under study.

The movement of arc cathode spots has been measured with virgin and with eroded Mo surfaces at various temperatures. The erosion process and the temperature influence the random movement only insignificantly. Since with virgin surfaces the cathode craters overlap it is concluded that the elementary displacement step corresponds to a crater radius in all cases, provided the surfaces are sufficiently clean. This result has consequences for cathode heating models.

Measurement of the relation between polarisation P and electric field E for lithium potassium sulphate (LiKSO₄) was made in the low temperature range below room temperature. The P-E hysteresis loops along the c axis of LiKSO₄ were observed in the low-temperature phase below the lower transition point T_t^l of about -70 degrees C, and in the intermediate phase below the upper transition point T_t^u of about -25 degrees C. These phases were found to be ferroelectric. The temperature dependence of the spontaneous polarisation P_s and the electric coercive field E_c were obtained.

The new method for analysing the non-integer kinetics order in thermoluminescence, reported recently by Moharil and Kathuria (1983) is discussed. The assumption that all traps are filled at high doses is considered to be invalid. A tentative calculation using their original data supports this argument and indicates the importance of the parameters A_s/A₀.

A flow equation for a continuously-flared viscometer capillary is derived. This equation is comparable with Poiseuille's equation for conventional capillary flow and apparently in the flared capillary case no additional (correction) terms are required. For a given capillary this must be confirmed experimentally.

A consistent set of high precision viscosity data for water at various temperatures and for 20, 30 and 40 per cent sucrose solutions is reported. These were obtained using a glass capillary viscometer with an extensively flared capillary. The negligibility of the kinetic energy correction term for this viscometer is confirmed. The reported viscosities are based only on the absolute viscosity of water at 20 degrees C. These data are recommended as reliable standards for capillary viscometer calibration.

Occupation probabilities of individual hyperfine sublevels of a ²³Na atomic beam were determined by laser-induced fluorescence spectroscopy in a magnetic field. This technique was applied to investigate in detail the nuclear polarisation in a polarised alkali ion source produced by a sextupole magnet and a high frequency transition.

The amplification characteristics of a N₂⁺ ion laser at 391.4 nm and 427.8 nm excited by fast discharge are studied. The small-signal gain coefficient and the saturation energy density of these two laser lines are obtained experimentally.

The operational characteristics of a discharge-excited XeCl laser utilising a discrete element pulse-forming network (PFN) are reported. A pulse output energy of 0.6 J, an efficiency of approximately 2% and an energy extraction of 4.5 J litre^-1 were recorded at a relatively low charging voltage. With neon buffer gas, pulses of 80 ns (FWHM) were measured.

It is shown theoretically that a relationship exists between the phase and amplitude components of the modulation transfer function (MTF) for a monomode optical fibre, provided that the source coherence time is very much less than the reciprocal modulation bandwidth: this condition is normally satisfied in practice. It follows that only the amplitude component need be measured; the phase component can then be derived. A similar relationship is also shown to exist for the phase and amplitude components of the complex amplitude transfer function. The result allows the MTF to be measured conveniently for a variety of propagation conditions, such as differing optical carrier frequencies or differing polarisation states. The corresponding relationship for the amplitude transfer function could be useful in spectroscopic applications.

Potential retardation measurements with a variable-length drift tube have yielded the most probable energies of O⁺ ions in He, Ne and Ar buffer gases at 300K for selected values of reduced field E/n. For He, E/n was in the range 60-210 Td, for Ne, 80-510 Td and for Ar, 95-630 Td. The most probable energies obtained agree with the mean energies predicted by Wannier's equation for E/n>200 Td assuming ion drift velocities calculated from the polarisabilities; a comparison is also given.

The drift velocity of electrons in hydrogen, nitrogen, oxygen, carbon monoxide, carbon dioxide, and air free from water vapour and carbon dioxide, at ambient temperatures (293-296K) has been measured by the modified Bradbury-Nielsen time-of-flight method over the range of the reduced electric field E/N: 0.05<or=E/N<or=250 Td, 0.1<or=E/N<or=250 Td, 1.0<or=E/N<or=275 Td, 0.1<or=E/N<or=150 Td, 0.6<or=E/N<or=250 Td and 0.05<or=E/N<or=400 Td respectively. The present results are compared with those obtained by other investigators.

Mixtures of inert and molecular gases are commonly employed in the neutron counters used for control and instrumentation in nuclear reactors. These counters are, however, often expected to have long lives under in-core irradiation conditions and this feature could be improved by the use of inert gases alone, provided a mixture with a sufficiently high electron drift velocity could be found. The present paper is concerned with a study, using Monte Carlo simulation techniques, of the electron transport properties of binary mixtures of the inert gases aimed at determining the most suitable filling for a counter. It is shown that He/Ar or He/Kr mixtures would seem to be most suitable for such a purpose.

Half-integer harmonics were observed in ionisation waves in SF₆ gas. The results are explained in terms of parametric excitation due to an interaction of externally excited waves with spontaneous ionisation waves.

A theory of coherent scattering is developed for the case of two beams with a Gaussian amplitude distribution, taking into account the effects of the curvature of the wavefronts. The received scattering power, the 'effective' scattering volume dimensions and the amplitude of the k-spectrum interval involved have been carefully calculated and the influence of the wavefront curvature especially investigated. Useful information both for reliable interpretation of the measurements on WEGA and the design of other coherent scattering experiments (with microwaves or far infrared) is achieved.

Electron heat transport is studied for a variety of presumed non-Maxwellian distribution functions in the presence of steep temperature gradients. For a representative group of distribution functions the heat flow in the region lambda _T/L_T approximately=0.1 relevant for laser-plasma interaction ( lambda _T is the thermal mean free path, L_T is the temperature gradient scale length) is much smaller than the free streaming value.

A new formula is derived which gives electron mobility values in argon in good agreement with experiment and calculation. The effect of mercury on electron mobility in argon is expressed as a correction factor. The theoretical expression obtained is applied to discharge conditions for which exact results are known, and the results are compared. The values of mu _e obtained have been used to calculate axial electron density, showing good agreement with experiment.

A multiple-arc discharge system has been developed enabling large volumes of ionised gas to be produced. A scanning monochromator has been used to determine the intensity distribution produced by horizontal multiple-arc discharges operating in different configurations carrying individual arc currents up to 20 A. Comparison of the results with those for a single arc show that coalesced multiple-arc discharges can be used to produce larger and more uniform volumes of ionised gas. Potential applications include heating gases and processing materials with the advantages of higher throughputs and uniform heating.

The role of the electrode surface and some gas phase processes in the production of electrons which initiate electrical breakdown is investigated. The results show that to achieve approximately constant secondary electron emission in these experimental conditions it is necessary to perform about 1000 breakdowns. The experiments indicated that the initial electrons are created by the impact of N₂ metastable states on the cathode and the nonradiative lifetime of these states depends on the gas pressure.

A method for a unidimensional space charge calculation in an ionised gas flow is described. Different ion species of different mobilities are present in the gas. The authors use analytical expressions for both space and potential versus local electric field. They apply this calculation to the space between plane parallel grids whose transparencies are computed from a model previously described. They compare results with an experiment made in ambient air and a good fit is found by assuming that only two ion species are present in the gas flow.

Measurements have been made of the energy balance of high-pressure sodium arcs in sapphire arc tubes under conditions of: (a) varying power from 200 to 600 W at a constant amalgam temperature of 700 degrees C; (b) varying amalgam temperature from 700 to 800 degrees C at a constant power of 400 W; and (c) varying mercury pressure from 0 to 1050 Torr at a constant power of 400 W and a sodium pressure of 65 Torr. Together with measurements of axis and wall temperatures, these results provide an excellent test of theoretical models. High radiation efficiency is favoured by high input power and mercury rich amalgam. The amalgam temperature hardly affects the radiation efficiency, despite a large change in arc temperature. A number of radiation processes which are individually insignificant contribute approximately=25% of the radiation and need to be included in model calculations. The infrared discharge continuum amounts to only 3-5% of the input power, but its origin remains a mystery.

A series of experiments is described in which slices of InP, homogeneously doped with radioactive silver, were subjected to heat treatments. At the end of these 'out-diffusions' the profiles of radiotracer silver in the slices were determined. The results were anomalous in the sense that they did not correspond to the expected solutions of Fick's law. In particular the measured profiles showed surface concentrations which exceeded the bulk concentrations. The conclusion is drawn that the diffusion mechanism for silver in InP is not a simple one and that the silver atoms must exist in the lattice in more than one form. An attempt is made to relate these results to a recent model for silver in InP. Reasonable qualitative agreement is found.

Ti films readily sorbed hydrogen up to an atomic ratio r=2.0 at a saturation pressure of 2*10^-3 Torr. The turning points on the curve of resistance R versus r were correlated with the phase boundaries. The maximum on this curve agreed well with the data of Wedler and Strothenk (1966), and gave the solubility limit for H in Ti films at 290K as H/Ti=0.07. The data for the work-function phi agreed fairly well with Magee's (1968). The phi curve showed that the Fermi level mu of the FCC hydride was 0.14 eV higher than mu of the FCT phase, and at least 0.28 eV lower than mu for the clean metal. These data are compared briefly with the results of modern calculations on the band structure. The FCC/FCT phase boundary was at r=1.8 at 20 degrees C and r approximately=1.85 at 50 degrees C, and the FCC/FCT transition temperature was >50 degrees C.

Electronic properties of organic thin films polymerised from p-xylene in plasma at 13.56 MHz were investigated from the analysis of photoconduction and high-field conduction. Hole injection from metal electrodes was found in both optical and electrical excitations. The barrier height and the ionisation energy were determined to be 2.07 and 6.90 eV, respectively. These properties resembled those of linear, crystalline poly-p-xylylene (PPX), obtained by conventional radical polymerisation.

Cd₂SnO₄ n-conducting thin films have been prepared by DC reactive sputtering from Cd-Sn alloy targets. The concentration of conduction electrons was varied over the range 7*10²⁵-3*10²⁶ m^-3 by the post-deposition heat treatment as well as by the variation of the content of the target. Temperature dependence of carrier concentration and Hall mobility in the temperature range 77-380K show the films to be degenerate semiconductors. Oxygen vacancies and interstitial cadmium ions are the postulated charge defects. The existence of neutral defects was also taken into account.

The ponderomotive force acting on dielectrics in non-uniform static electric fields is time dependent with a time constant which is a function of the permittivity and conductivity of the dielectric and of the surrounding medium. An experimental study of the dependence of this force on the conductivity of the dielectric is reported. The time constant for the time dependence decreases with increase of conductivity. The final stationary value of the force increases with conductivity for conductivity values typical of good insulators.

Partial discharges in cavities lead to the deterioration and breakdown of insulating media. Ion and electron bombardment have been considered as independently accountable for failure of dielectrics by sustained partial discharges. Electron bombardment is the dominant cause of damage. The rate of degradation is accelerated by increasing the frequency, magnitude and time of applied voltage. The main contributing factor in discharge damage is the kinetic energy of the electrons. The effective life of the dielectric is inversely proportional to the average kinetic energy of the bombarding electrons. The mechanism of dielectric breakdown by partial discharges in cavities is explained primarily by electron and ion bombardment. The technique of filling the cavities with insulating gases at higher than atmospheric pressures, or with insulating liquids, will decrease the rate of deterioration and increase the effective life of the dielectric. The present analysis attempts to correlate and justify the experimental findings with theory.

The ion yields and energy distributions of C^- and C₂^- ions sputtered from a graphite target by a 20 keV Cs⁺ beam, have been measured in the temperature range 80-880K. Assuming a velocity-dependent ionisation probability, the measured changes in the position of the peak of the energy distribution have been used to calculate the changes in the work-function of the emitting surface. It is concluded that the work-function reaches a broad minimum (and the ion yield a maximum) at approximately 500K increasing thereafter by about 1.3 eV at the maximum achievable temperature in the experiment; this increase is accompanied by a corresponding decrease in the negative ion current by about a factor of 6.