Table of contents

Letp₃=p_sexp(13·3815t-1·9760t²-0·6445t³-0·1299t⁴) where t=(1-T_s/T), T is absolute temperature, suffix s denotes the steam point and p_s is standard atmospheric pressure, exactly 101 325 N m⁻². Then p₃ differs from the saturation pressure p of water vapour over a plane surface of the pure liquid phase at temperature T, as predicted by the generally accepted formulations, by less than ±0·1% of p at all temperatures between −50 and 140°C.

Effect of turbulence in one arm of a laser amplitude division interferometer on the visibility of fringes is studied. It is shown that the visibility is strongly dependent on the magnitude of turbulence.

The response of a pressure scanned reflection echelon to a Voigt profile (Doppler-broadened Lorentzian) is expressed analytically. The effects of surface imperfections of the echelon plates and the finite width of the exploring diaphragm on L-D determination of a spectral line are considered.

Uniform field steady-state ionization currents were measured in dry air as a function of N at constant E/N (E is the electric field strength and N the gas number density) and constant electrode separation d for 14·13 × 10⁻¹⁶ less-than-or-eq, slant E/N less-than-or-eq, slant 282·5 × 10⁻¹⁶ V cm². Uniform field sparking potentials were also measured for Nd range 1·24 × 10¹⁶ less-than-or-eq, slant Nd less-than-or-eq, slant 245 × 10¹⁶ cm⁻². The ratio of the Townsend primary ionization coefficient α to N, α/N, was found to depend on E/N only. The secondary coefficients were also evaluated for aluminium and gold-plated electrodes for the above range of E/N. Measurements of the sparking potentials showed that Paschen's law is not obeyed in air at values of Nd near and below the Paschen minimum.

Studies of cathode spot division have been made for vacuum arcs with solid metal cathodes of zinc, lead, copper, aluminium and bismuth for discharge currents in the range 5-150 A. The distribution function of the number of spots is Gaussian for fixed experimental conditions. Above a certain current i0 the mean number of spots increases linearly with current except for bismuth. A model for spot splitting is proposed which is based on the energy balance at the cathode surface and temperature-field emission for electrons.

The variation of discharge current in a transverse magnetic field (0-300 G) has been studied in the positive column of a glow discharge in air, carbon dioxide, hydrogen, helium and neon within the pressure range of 80 to 200 mtorr. The current gradually rises with the increase of the magnetic field, then attains a maximum value at a particular value of the magnetic field which is the same for all the gases and independent of pressure for the same initial discharge current, and then gradually decreases. The value of the magnetic field at which the discharge current is maximum is found to be proportional to the square root of the initial discharge current and the maximum value of the current is inversely proportional to pressure in all the gases; utilizing Beckman's expression for the axial electric field and the radial electron density distribution in a transverse magnetic field, a mathematical expression for the discharge current and its variation with magnetic field has been deduced. The theoretical results are in qualitative agreement with experimental observations and the causes of discrepancy have been attributed to (a) limitations of Beckman's expression for electron density distribution and axial electric field and (b) absence of data for fraction of energy loss in collision and that of the electron temperature at E/P values at which the present observations have been made.

Induction velometry with two-dimensional non-uniformities of velocity and magnetic field has been analysed. Assuming the distributions of velocity and magnetic field, the expression of the induced potential gradient has been obtained with the method of integral relation.

Microwave interferometric techniques have been applied to the measurement of dielectric constant and dielectric losses in n-pentanol from 400 MHz to 4000 MHz at temperatures of 0°C, −10°C and −25°C. A definite distribution of relaxation times is clearly shown at these temperatures for the second dispersion region. A Cole-Cole distribution function independent of temperature in the range investigated fits the data within an experimental error of 1% for both the real and imaginary parts of the permittivity, and the value of the high-frequency dispersion parameters have been derived.

The diffusion and size distribution of chromium aerosols with particle sizes between 0·002 and 0·01 μm have been investigated with Nolan-Pollak nucleus counters. It is shown that there is a considerable decay in particle concentration by diffusion to the internal surfaces of the counter during normal operation if particle size is less than 0·01 μm. Measurements indicate that the decay corresponds closely to that given by the theory of diffusion from a stationary aerosol in a long cylinder. This result leads to a simple `static decay' method of size estimation which is compared with the diffusion battery method.

The growth of an electrical discharge in transparent liquids can be observed using a simple shadowgraph technique. The photographic recordings resemble those obtained using the Lichtenberg technique. However, the shadowgraph system has the advantage that the test liquid is not disturbed by the recording medium.

Preliminary observations reveal basic differences between the point-cathode and point-anode discharge phenomena.

Low frequency, internal friction measurements made as a function of temperature on pure indium in single crystal form have shown three effects which could be resolved into the following three separate mechanisms: (i) A frequency insensitive peak in internal friction observed at about 170 K is believed to be associated with the motion of twin boundaries; (ii) A relaxation measured at about 273 K is interpreted as originating from the motion of dislocations interacting with vacancies; (iii) A background relaxation between 320 K and the melting point is attributed to dislocation climb.

When powerful radiation bursts interact with solid targets the ejected material escapes in a peculiar sheet-like form with hyperthermal velocity. An attempt is made to explain this phenomenon by the action of a thermomechanical shock wave which is generated in the target and ejects the heated surface layer with twice the particle velocity of the shock. The theory has been tested for electron pulses for which a simple one-dimensional approach is possible. Extension of the presented theory to laser pulses gives the proper order of magnitude for the plume velocity and other observed phenomena.

The effect of a magnetic field on the generation of microwave harmonics in n-InSb is investigated by considering the energy dependences of carrier mass and relaxation time as the sources of nonlinearity. The generated harmonics show a common maximum at ω_e0=2 × 10¹² rad s⁻¹ for ω=15 × 10¹⁰ rad s⁻¹; other resonances are not marked. However, the helicon effects are much pronounced. The amplitude of the third harmonic helicon mode increases with increasing magnetic field, while other modes of harmonics show a decrease.

The dc conductivity, the dielectric constant and the dielectric loss at 100 kHz and 3·6 GHz, have been measured for samples of potassium nitrite and potassium nitrate over a wide range of temperature. The dc conductivity and the dielectric constant show anomalies at −13°C and 40°C in a crystal of KNO₂ pulled from the melt. However, the dielectric anomaly at 40°C does not indicate a ferroelectric-paraelectric phase transition and the room temperature phase of KNO₂ seems not to be ferroelectric. The dc conductivity, the dielectric constant and loss measured in a randomly oriented single crystal, grown from aqueous solution, and a sample prepared from a melt of potassium nitrate, show anomalies at about 130°C on heating, and at about 124°C and 108°C on cooling. The dc conductivity, dielectric constant and loss value of the two samples of KNO₃ together with the frequency effect in a melt sample of KNO₃ are reported.

Caesium-antimony photocathodes were processed in a vacuum of the order of 10⁻⁹ torr in two types of ultra-high vacuum systems, namely, (i) a conventional rotary pump-three stage glass mercury diffusion pump combination system and (ii) a sorption pump-titanium sputter ion pump combination system. Enhancement in white light sensitivity was observed when the photocathodes were processed in the ion pump uhv system in comparison with the diffusion pump system. A brief discussion is presented in the light of the residual gas contents in evacuated tubes processed in uhv systems. The photoelectric yield of semitransparent caesium-antimony photocathodes depends critically on the thickness of the original antimony film. Hence, the relationship, photoelectric yield (μA/lm) against percentage transmission of antimony film has been established. It is found that thin film caesium-antimony processed from an antimony film with 70% transmission yields an efficient photocathode in both types of uhv systems.

Single-crystal films of nickel have been deposited in ultra high vacuum under closely controlled conditions, with a resulting high standard of lattice perfection as determined by electron microscopy. Anisotropy measurements made by torque magnetometry yielded the following conclusions:

1. K₁ has the same value as for bulk nickel (−5·0 × 10⁴erg cm⁻³ at room temperature). The magnetostrictive behaviour is predictable from bulk properties. An estimate of the order ofK₃ is also obtained (−3 × 10³ erg cm⁻³).

2. K_u can be reduced to extremely low levels by taking steps to exclude all known mechanisms.

3. The effect of stress on both K₁ and K_u have been investigated and correlated. A constraint temperature (about 110°C), well below the substrate temperature during deposition, has been established.

4. No contribution to K_u from mechanisms involving oxygen has been observed.

5. The effects of lattice imperfections are quite marked, and can be the predominant K_u source.

The temperature dependence of the coercive fields in aged CuNiFe and CuNiCo has been measured between 300 K and 77 K. The results are interpreted in terms of shape anisotropy of the ferromagnetic phase of the alloys and the variation of ferromagnetic particle volume with ageing time is deduced from the results. An arrest of the volume increase with ageing time is attributed to the start of coherency loss between the ferromagnetic and paramagnetic phases of the alloy when the diameter of each lamellar interface is about 600 Å.

It was pointed out by Schön in 1958 that the analysis of thermoluminescence and thermally stimulated conductivity can be simplified by using a quadratic rate of heating. The fact that such a rate of heating is feasible in practice has given a stimulus to review the theories of TL and TSC in this light. In this paper it has been shown that in the second-order kinetics of the Garlick and Gibson model, theoretically the TSC curve should not exhibit any peak with the quadratic rate of heating under charge neutrality condition, rather it should tend asymptotically towards a constant value. Thus the usual methods of analysis utilizing the temperature of maximum TSC for the estimation of trap depth would not be applicable. This non-occurrence of the peak is found to be due to the temperature dependence of the mean lifetime of the free electron in the conduction band.

Two peaks were found in the high temperature region for LiF thermoluminescent phosphor TLD-100. The total area of these two peaks increased with dose to a saturation value at about 4 Mrads. By extrapolation, a threshold dose of 1 krad was required to produce these two peaks. An investigation, using a thermal annealing technique, showed that these two peaks do not fit the Randall and Wilkins model. Evidence from optical absorption showed that these two peaks are probably connected with V-centres (hole traps). An attempt has been made to correlate the supralinearity and sensitization behaviour to these two peaks.