Table of contents

The aspects discussed include the physics of electron energy-loss spectroscopy in the context of a transmission electron microscope; the information which can be derived from energy-loss spectra; the properties of various spectrometers and the practical factors which govern their performance; the techniques of data acquisition and reduction. Examples of the application of this technique to problems in materials science and biology are cited.

A remarkable improvement in the performances of a pre-existing transient recorder is inexpensively obtained by using a simple microcomputer which controls repetitive signal scan operation. Final data are displayed on a scope and, on external command, punched on paper tape support for further off-line processing. The setup results in a more efficient data acquisition with enhanced signal-to-noise ratio.

A measurement facility is described which provides direct digital output of the electrical resistance of a metal sample, immersed in He II at 1.7K, with an uncertainty of less than 8*10^-10 Omega and a linearity of +or-0.005%. When it is used to measure the concentration of thermally induced (quenched-in) vacancy-type crystal lattice defects in copper and aluminium the equivalent concentration sensitivity is about 10^-8. The system uses a microprocessor-cased control and calculation program stored in a non-volatile memory for ease of operation when the equipment is switched on or off.

A modification of the Weibel radio frequency line generator is described. The modification substantially reduces the necessary number of spark gap switches and yields both a significant saving in construction costs and a greater ease of construction and reliability of operation. The construction and performance of an eight-period line generator incorporating this design modification are described. The equivalent root mean square open-circuit voltage and generator impedance are 14.1 kV and 9.7 Omega .

A method is proposed for calibrating vacuum gauges down to 0.1 Pa. The necessary apparatus is easily constructed out of simple laboratory equipment and can be readily calibrated by the user. An uncertainty of 10% is easily achieved. The method is ideal for calibrating Pirani and thermistor gauges under industrial conditions.

The attachment allows scanning powder samples over a range of 0 degrees -52 degrees , under either low hydrothermal conditions i.e. 240 degrees C and 34*10⁵ Pa or with temperatures up to 400 degrees C and pressures from low vacuum to 6 MPa in any gas atmosphere.

Two techniques are described for making lightweight silica glass buckets for weight-gain type kinetic experiments, in which it is necessary to contain spalled reaction products. The buckets are 25 mm diameter by 12 mm deep. They weigh 1-1.5 g, with wall thicknesses of 150-225 mu m. Methods of handling fragile silica glass during the various glass blowing operations are discussed.

Many commercial high-resolution NMR spectrometers employ a single receiver coil tuned both for observation and field stabilisation frequencies. As a result the potential sensitivity of the detector is decreased and removal of the double tuning offers a practical method of obtaining a higher signal-to-noise ratio for a given sample. This method has been applied to the measurement of ¹H, ¹³C and ³¹P NMR spectra.

The fringe control techniques are of immense importance for removing high spatial frequency fringe patterns arising as a result of the overall motion or gross structural deformation of the object when it is subjected to a stress field. The removal of these high spatial frequency fringe patterns is necessary to observe the region of defect in the object vividly. A simple method of fringe control for these unwanted fringes is described.

Data from a pressure sensor are stored sequentially in EPROM (erasable programmable read only memory) memories which replace the magnetic cassette commonly used. An all-in-one chip microprocessor controls the data acquisition and recording system. The instrument is working at the harbour of Genoa to record the longitudinal free oscillations of the Ligurian Sea.

A resonator is described which has been used to study conduction electron spin resonance (CESR) in a metallic sample. For CESR studies this resonator is advantageous over conventional reflection microwave cavities because the sample is simply a flat plate.

A new method is described for reducing errors in measurements of random pulses rate due to dead time losses. It is based on the inverse of the process causing the error. The losses happen when two (or more) events are too close and produce one pulse. In the correction system some pulses are counted more than once according to a law similar to the one valid for the losses.

A low-frequency sinusoidal current source is described with a stable current output (1 part in 10⁴ over 24 h). The design also offers a three-terminal current-balancing facility which enables accurate and stable nulling of unwanted ohmic voltages in Hall effect measurements.

A simple and inexpensive method to record and process low-energy electron diffraction (LEED) intensities (I-V curves) is presented. A closed-circuit television system and an electronic interface allow the selection of one spot at a time. The raw data are corrected for background, beam current and transmission of the LEED optics. The intensities can be measured directly from the screen or from a television recorder.

With simple interfacing the following features could be achieved: accumulation of weak luminescence spectra by scanning several times over the region of interest; digital data acquisition from a photon counting system, thereby eliminating problems with earth loops and noise; closed loop control system of averaging; and immediate data evaluation during the experiments.

A new technique of multicolour radiation pyrometry is described. The directional emissivity of the surface whose temperature is being sought is estimated from measurement of the surface reflectance factor. Temperature measurements of a tungsten strip lamp in the range 1180-1680K using this technique agree within 0.3% with those obtained from its spectral radiance temperature and published emissivity data of tungsten.

In the method described, the torque is proportional to the rotational hysteresis loss per revolution and is measured by the change in rotation frequency of the rotor of an air turbine which contains the sample. The method has been used to determine the peak in the rotational hysteresis curves of two basalt samples and is also sensitive enough to measure sandstones. The minimum measurable torque exerted on a sample up to 12 g in mass is about 10^-7 Nm but the system is capable of further improvement in sensitivity if required.

In order to obviate the complementary limitations of velocimetry by laser fringe anemometry and by photographic particle tracking, a family of optical systems is described which is suitable for both types of measurement over extended test regions. It is based on a thin sheet of light from a powerful CW laser which is broken into fine interference fringes in its plane and interrupted at a known frequency. Depending on the divergence and energy density of the beam, various applications are considered ranging from test areas as large as those required in fire research to those more characteristic of high velocity applications which involve test space dimensions of several centimetres. The conflicting criteria of visibility of tracer particles and their ability to follow variations in gas flow are examined for these regimes. Among other capabilities of such systems are the addition of a third dimension by using multiple sheets of light, and the use of the fringes as visible 'ray trajectories' in deflection tracing through refractive index gradients.

The thermoelectric properties of electrical conductors in the form of sheets and covered with an electrolytic deposit of a different nature are due to induced currents passing across the surface separating the superposed conductors. These currents are proportional to the instantaneous value of the calorific flux located in the electrolytic deposit. This particular thermoelectric effect has been used to develop a new solution to the problem of measuring superficial calorific fluxes and temperatures.

An automated technique for measuring capacitance and conductance of semiconductor devices over a wide frequency range (50 Hz-1 MHz) has been developed. Measurement accuracies are demonstrated to be within 1% of capacitance and 2% of conductance in the frequency range 50 Hz to 300 KHz. Bias levels can be programmed automatically by a digital to analogue converter from -10 V to +10 V.

The operation of a CO₂ transversely excited (TE) waveguide laser using capacitor discharge excitation and pulser sustainer excitation results in specific output energy densities of 85 mJ m^-3 Pa^-1 and 113 mJ m^-3 Pa^-1 respectively. The 3.7% efficiency achieved for the laser when operated in the pulser-sustainer mode is the highest reported for a CO₂ TE waveguide laser. Assessment of the waveguide losses results in a correct prediction for the polarisation of the laser output. Consideration of the sustainer discharge allows the arcing limit of the discharge and the form of the sustainer current to be determined.

Methods are described for determining the in situ volume fractions of materials flowing in pipelines. By using a number of discrete gamma -ray energies the method can be extended in theory to cover as many different types of material as required. In practice, clearly defined gamma -ray energies are required and the materials must have substantially different absorption coefficients. Results are presented for oil-air, oil-water and air-water mixes and for the oil-air-water combination. Applications are presented for homogeneous, annular, and stratified flow patterns.

A typical double collecting mass spectrometer was greatly improved by the use of a device which enables automatic measurements of isotopic ratios in digital form to be carried out. The system consists of two electrometers with high value resistors being automatically replaced by capacitors for the ratio measurements. Thus noise produced by the resistors is eliminated. The electrometer output signals are digitised by a digital voltmeter, and the digits plus some additional information are transferred to a calculator printing the signals and their ratio.

The damping of a tightly stretched circular nickel grid vibrating at a few kHz in air, in gaseous ⁴He, in liquid He I and in liquid He II is investigated. With experimental error, all the data can be plotted on a universal curve of Delta omega / omega _{0 rho 1} against lambda , where Delta omega and omega ₀ are respectively the width and centre frequency of the resonance, ^rho 1 is the density of the medium and lambda is the viscous penetration depth. The nuisance damping is small. It appears feasible to develop a vibrating grid viscometer which could with advantage be applied to certain specialised situations and, in particular, to the superfluid phases of liquid ³He.

An improved apparatus for determining the fracture strength of brittle materials by a hydraulic bursting technique is described. The new design greatly reduces the number of specimens which fail at their edge and reduces the scatter in the results. To complement this, a more detailed theory is developed to analyse results. An investigation of the strength of silicon nitride as a function of the impact velocity of a water jet illustrates the use of the apparatus. A method for converting fracture stress data to equivalent flaw size data is given which allows a more physically meaningful and useful presentation of results.