Table of contents

The uses of optical gratings in linear and radial measurement are reviewed historically. They are shown to involve a 'self-improving' principle which is applied to the generation of the gratings themselves and to the transducers used in reading them. Accurate automatic measurement is thus made available to a wide range of laboratory and engineering applications.

A simple calculation is presented for determining both the first virtual object plane in a space charge limited electron gun and the angle of beam divergence. Significant differences are obtained from the Davisson-Calbick formula as applied to a space charge limited diode.

A simple coaxial termination for immersion in liquid nitrogen is described. It provides a UHF noise reference, stable over long periods.

Measurements of the corrosion of steel components, such as nuts and bolts, in nuclear reactors present special problems because of the restricted access and the hot ( approximately 100 degrees C), radioactive (10 rad h^-1) environment which exists even during a reactor maintenance period. To operate in such conditions a small self-contained instrument package has been developed which can be continuously cooled and remotely controlled. It makes use of the fact that when the beam from a high power ruby laser is focused on to a point on the surface of the corrosion layer a certain depth of the layer is penetrated. When this penetration extends down to the bare metal the surface reflectivity increases substantially, and it has been found that the depth of corrosion at any point can be measured accurately by monitoring the reflectivity of the probed area using a low-power gas laser. The reflectivity of the corroded surface to the gas laser beam has been shown to have a characteristic variation with the number of high-power ruby laser pulses fired and rises sharply when the corrosion layer is penetrated. By comparing the total energy required to penetrate the corrosion layer with a calibration curve obtained on samples with known corrosion depths, the depth of corrosion on the steel component can be determined.

A double-tilting side-entry specimen rod which has sapphire bearings on one axis of tilt has been made. A feature of the device is the ability to remove and interchange the specimen mounting block.

A new RF gate design is presented, utilizing an integrated circuit double-balanced mixer. The gate operates from any standard variable frequency oscillator and pulse-train generator and produces phase-coherent pulses of very high stability. The carrier suppression exceeds 60 dB and, subject to other component ratings, the theoretical upper frequency limit is 450 MHz.

A stationary high-level Gaussian noise is generated by smoothing an optimum m-sequence which is selected by the cathode-ray tube method.

Observed asymmetric resonance profiles may suffer from instrumental broadening. A simple and accurate method of determining the true resonance centre of such broadened profiles is described.

A compact holographic system, with minimum components, was developed for field work in geophysics and foundation engineering. By recording the variations of a bore hole wall on a holographic film, it is possible to reconstruct it three-dimensionally, and to evaluate this record with high accuracy.

An ultrahigh vacuum chamber has been constructed in which it is possible to carry out measurements of electrical conductivity and thermally stimulated conductivity on cadmium sulphide films, in order to observe and characterize the isolated defects introduced by low energy inert ion bombardment of the surface at low temperature. So that a clean surface is presented for investigation, the CdS films are produced in situ and subsequent ion bombardment and measurements take place with no intervening exposure of the samples to contaminant gases.

A simple and versatile, but also sensitive and accurate method of determining vibration amplitudes is presented. The method consists of observing the slow motion of a moire pattern formed by the image of a signal grating projected on to an identical reference grating, illuminated by stroboscopic light. The pitch of the image of the signal grating can be suitably adjusted to yield an optimum relation between line frequencies of the two gratings. Full control over the sensitivity of the system is therefore possible. The accuracy and resolution of the method are comparable with those of other known methods based on sophisticated vibration measuring equipment.

Describes a new reliable and stable light scattering instrument. It is based on photographic techniques and presents two possibilities of recording the scattering patterns: a flat and a circular camera. The flat camera is more suitable for low angle scattering measurements, whereas the circular camera provides the new possibility of recording a two-dimensional angular spectrum of intensity at high angles. The optical system offers both the use of a partially coherent green radiation from a mercury lamp and of the more coherent red radiation from an He-Ne laser. In addition to the optical system, the instrument is equipped with the facility of monitoring and studying the structural and morphological changes which occur with deformation in materials. For this purpose, two mechanical devices have been designed and built to be used in conjunction with the optical system. The main corrections required are discussed.

The construction of a three-stage tunable birefringent filter using variable phase shifters fabricated from ammonium dihydrogen phosphate is described and its performance, evaluated for white light with a divergence of 2-3 mrad, is found to compare well with the predicted behaviour. A brief description of the principles of operation is included. Theoretically, the filter scans the spectrum from 250 nm to 750 nm with a bandwidth ranging in value from 35 nm at 250 nm to 85 nm at 750 nm. Theoretically, the voltage necessary to scan the above spectrum range is +or-25 kV. Experimentally, a bandwidth ranging from 41 nm at 350 nm to 80 nm at 700 nm was obtained. Losses at various wavelengths have been determined. For example, at the centre wavelength (500 nm) where the bandwidth was 47 nm a ratio of I_out/I_in=1/15 was obtained. Causes for deviation between theoretical and experimental results are examined and suggestions made for further work.

The requirements for a transmission stage for the scanning electron microscope (SEM) are discussed, and an advanced stage meeting this demand is described. Examples are shown of high resolution micrographs and selected area diffraction patterns obtained using the stage.

A high-vacuum specimen chamber was constructed for a Siemens electron microscope in order that in situ studies of the growth of refractory metal films may be performed under clean well-defined conditions. The chamber is differentially pumped and reaches a vacuum of 0.1 mu Torr with the rest of the column at about 20 mu Torr. The hydrocarbon contamination rate at the specimen is approximately 2.5 AA min^-1 compared with about 500 AA min^-1 for the unmodified instrument. The stage operates smoothly, and images at 80000* are steady and free from vibration.

The flux-time waveform from a mechanically chopped laser beam is used to find a Gaussian pattern approximating to the distribution of energy in the beam. The technique, which is insensitive to errors in locating the beam centre, has been used to measure the minimum radius of a carbon dioxide laser beam having a continuous power of 2 kW focused into a region less than 2 mm in diameter.

A rugged and simple device for monitoring the output of pulsed CO₂ lasers is described. Consisting simply of a cylinder of germanium through which the laser beam is passed, it makes use of the photon drag effect to measure the profile of the radiation pulse.

A method of compensating for the effects of stray capacities on the measurement of carrier concentration profiles is described. This allows a versatile mercury Schottky barrier probe to be used for the rapid and accurate measurements of epitaxial gallium arsenide.

An improved technique has been developed for the strain- free preparation of metal single crystals with large uniform thin areas (up to 15 cm²) in the thickness range from 5 to 100 mu m. The method consists of electrolytic jet polishing combined with a continuous thickness measurement which governs the polishing current density. The periphery of the specimen may retain its initial thickness, reducing the danger of deformation during subsequent handling. Ag, Al, Cu and Nb crystals have been prepared with this device for different experiments.

An apparatus is described for zone melting refractory metallic materials by means of radio frequency induction heating. A novel feature is the use of an eddy current concentrator to produce the high field strengths required to melt materials with melting points in excess of 3000 degrees C. Inert atmospheres are used at pressures slightly in excess of atmospheric pressure in order to suppress evaporation from the molten zone.

Describes an apparatus and a heterojunction that can be used under 2.6 eV, for any temperature; these were used for measurements of electroreflection by a surface barrier. Delta R/R of 10^-6 was measured with a voltage modulation of 0.2 mV. Quantitative measurements showed that there were few surface states and that the radial electric field was homogeneous. A magneto-electroreflection spectrum of Ge shows an example of use at low temperature.

An apparatus is described for continuous measurements of hydrocarbons in air. The sample, vapours as well as aerosols, is analysed in a flame ionization detector of a special design, which works at a reduced pressure. To achieve this, a carbon dioxide driven aspirator is utilized as suction pump. The detector is thermostatically controlled by combustion of hydrogen gas in a catalytic heater. The instrument is independent of electric current sources, apart from some common dry cells for the electrometer and the recorder. The built-in gas containers give the apparatus an operation time of 24 hours. The sensitivity for gaseous hydrocarbons and aerosols is about 0.05 mg m^-3 for most hydrocarbons.

Gaussian noise sources with spectra extending from DC to the megahertz region can be designed by utilizing resistance noise and the very low noise properties of JN FET. By frequency changing the noise output of a medium frequency JN FET amplifier it is possible to obtain a spectrum which extends down to DC essentially. An instrument using these principles has been constructed and has shown that it is feasible to achieve a source of noise which is uniform and of known spectral density over eight decades of frequency with an accuracy of 0.2 dB.

A simply constructed gravitational analogue of a cylindrical electrostatic field is used to study the orbits of charged particles in such fields. The phenomena of deflection dispersion and focusing are all readily produced. Some of the more important characteristics are displayed in photographs of the orbits of steel balls in the model.

The geometric factor of a particle detector having either circular or rectangular geometry is derived analytically. Both isotropic and 'cos² theta ' variations of intensity are considered. An approach based on 'shadow areas' is applied to the case of particles passing through two unequal circular areas, and it is proved that the results are identical with those obtained previously using an approach based on the direct integration of 'infinitesimal areas'. This latter approach is then used for the case of two unequal rectangular areas, which has not been considered previously. The analytical results confirm those obtained previously using numerical techniques.

An absolute metastable atom detector which utilizes the principle of secondary electron emission from a metal surface is described. The secondary electron emission coefficient of the detection surface is maintained constant by continuous deposition of metal on to the surface. The detector is suitable for the continuous measurement of a metastable atom beam flux of the order of 3*10⁶ atoms/s or greater in a background gas pressure as high as 1 mu Torr.

A cold cathode discharge (trigger) vacuum gauge of the Penning type has been calibrated for nitrogen, argon, helium and neon over the pressure range 1-10⁺³ mu N m^-2. The pressure against discharge current characteristics were found to consist of a series of smooth curves joined by sharp jumps or abrupt changes of gradient. Mode changes in the discharge were observed by monitoring the change in RF radiation emitted by the rotating electron space charge. It was found that the jumps and changes in gradient observed in the calibration of the gauge occur at the same pressures as a doubling of the RF radiation frequency thus confirming the supposition of several previous authors that the discontinuities coincide with mode changes in the discharge. Finally, an explanation based on the variation of the axial potential in the discharge cell is advanced to explain the observed nonlinearity of the pressure against discharge current calibration.

A method is presented for checking the consistency of air velocity calculation from hot wire anemometer measurements in an air flow which undergoes a continuous variation of density with time. The method gives a means of checking correction factors applied to ambient wind tunnel calibration tests to allow for variable density conditions. A particular application of the method to air velocity measurement in a motored internal combustion engine is discussed.

A pressure rig is described in which a specimen may be placed and its volume measured while it is subjected to high pressure at a controlled temperature. The pressure which can be applied is over 100 MN m^-2, and tests have been carried out at 25 and 60 degrees C with the possibility of increasing temperature for further tests. A method of measurement and data treatment enables relative errors to be reduced to a low value, better than ¹/₂% of reading, and discrimination between specimens composed of different material and condition is obtained.

A theoretical investigation indicates that pressure differences in low velocity water flows can be measured accurately by means of a standard air-type manometer in conjunction with twin reservoirs in which free surfaces are formed. Surface tension effects and zero creep due to rate of change of temperature effects are thereby greatly reduced. Experience confirms these conclusions and water velocities as low as 0.03 m s^-1 have been measured using pitot-static tubes.

A relaxation dynamometer is described for the application of a constant force down to 30 nN on a body suspended in a fluid. Displacements are observed to within 1 pm. This has been applied to fluids including a silicone oil, glycerol at various temperatures and molten sodium isovalerate at 220°C. Illustrative examples include what appear to be critical limits preceding irreversible movement in the mesophase of sodium isovalerate.

A commercially available Robinson NMR oscillator has been adapted to provide a high-speed field tracking proton magnetometer covering the range 2.4-4.7 kG. Particular features of the instrument are an inherent search characteristic with search rates as high as 350 G s^-1, and a 2 ms response time to field changes using 217 Hz field modulation of only 1.8 G peak to peak. Extremely high locking accuracy is achieved with the oscillator frequency deviation less than 1.3 Hz RMS in a constant field. This performance is made possible by using a new type of detector which measures each resonance position independently, and which is inherently free of zero drifts and systematic offsets. The instrument is designed as a sampled-data system, and it can achieve the forward transfer function G(z)=1/(z-1) giving complete error correction in one half cycle of the modulation. Measured and theoretical responses to a step function of magnetic field are compared. A frequency to voltage converter is incorporated which enables high-resolution ESR spectra to be plotted as a function of field. The instrument also serves as a very flexible field programmer and has proved valuable in locking the magnetic field to the address ramp of a signal accumulation over long periods.

A new system comprising a very thin belt drive serving also as the suspension for a high speed rotor has been tested and proved feasible. Speeds of 740000 rev min^-1 and acceleration fields of 4000000 g were attained, the limit being set by rotor burst strength. A simple model describing the influence of ambient pressure, drive ratio and rotor material on the maximum attainable speed and centrifugal acceleration for a given rotor diameter is presented. The system offers potential use as a preparative centrifuge and for the mechanical testing of miniature material specimens, paints, adhesives and electroplatings.

A sweep generator has been used to control the field of a large electromagnet by connecting it to the external reference input of the magnet current supply. A ramp voltage is generated which can be run up or down between 0 and +5V and also be stopped at very precise and reproducible predetermined levels. The range is easily extended to 20 V without any major change of components.