Table of contents

A real-time electron beam testing system is described which consists of a scanning electron microscope, a very fast secondary electron detection system and a digitising oscilloscope. The system enables one to measure the signal with logic swings between 0.4-4 V and repetition rates of from 100 Hz to 100 MHz with a high time resolution of 10 ns: a signal with a very low duty factor of 10^-6 is measurable.

Automatic shearing correction of magnetisation curves of samples with a demagnetising factor is made using an additional fluxmeter that provides a signal proportional to the internal field that acts on the sample, allowing a direct representation of the true magnetisation curves. This gives rise to a great increase in the resolution of the measurement of magnetic parameters, mainly in soft magnetic materials.

A novel infrared scattering probe for enumeration of bacteria in broth cultures is described. The instrument enabled rapid, continuous and accurate monitoring of bacterial numbers ranging from 10⁴ to 10⁸ colony-forming units per ml.

The authors have developed a Si:P doped bolometer with fast response time for detecting heat pulses. The detector has been tested in a magnetic field up to 6 T showing that responsivity increases as the square of the field. An accurate calibration of the detector is made by comparing the responsivity measured from the load curves and from the time-of-flight spectra of ballistic phonons.

Describes a very economical and effective modernisation of a 1970 Micromass Model 602 mass spectrometer. Performance is greatly enhanced, both in terms of the precision of the results obtained and in the provision of facilities that are expected in a modern instrument.

A simple device has been used to measure the desorption rate of 13X molecular sieves at high temperatures and the air adsorption isotherm at low temperatures and pressures. The desorption rate is found to drop exponentially at high temperatures, and the absorption isotherm at low temperatures and pressures is lower than those of Stern and Dipaolo (1967) and Jackel and Bartel (1980).

An extremely simple arrangement provides a new interference method for the examination of the macroscopic relief of surfaces such as paper to which conventional interference methods are not applicable. Like several earlier techniques, it uses illumination at near-grazing incidence to generate fringes which contour the surface at much larger intervals than is the case when near-normal incidence is used: the fringes can be viewed at any angle. A possible explanation involving a mixture of specular and diffuse reflection at the test surface is proposed for the formation of the observed fringes. It is expected that the new method will have practical applications in materials science, particularly in paper technology.

A dynamic calibration method for a constant-temperature hot-wire anemometer is presented. A calibration apparatus produced a reference velocity field of the form upsilon (t)= upsilon _c sin omega t, where upsilon _c is the velocity magnitude and omega is the frequency. Placement of a hot-wire in this field provided data for calculating a dynamic Nusselt number. Results showed that a dynamic calibration is needed because dynamic heat transfer differs from steady-flow heat transfer.

Describes a tomographic flow imaging system based on capacitance sensors. It uses eight capacitance electrodes to perform a 'body scan' of the fluid-conveying pipe, and a linear back projection algorithm is developed to reconstruct the cross-sectional image of the two-component flow from the measured capacitance values. A prototype system has been successfully assembled and reconstructed images of static distribution models are presented. Possible industrial applications and practical limitations of the system are discussed.

Photomultipliers with a GaAs photocathode are used in the Thomson-scattering diagnostic for electron temperature measurements in the TORTUR tokamak because of their good sensitivity to near-infrared light. Unfortunately, these cathodes are extremely vulnerable and therefore gating is necessary. A 10 mu s-pulse circuit has been constructed to gate the first, third and fifth dynodes, which resulted in an on/off ratio of the gain of 2*10⁴. The dark current was diminished by three orders of magnitude down to 0.02 nA. This method of gating has been successfully applied to photomultipliers with different dynode structures. Together with a mechanical shutter, calibration on a tungsten filament has been performed without using attenuators and/or diffusers. The sensitivity of the photomultipliers remained constant within several per cent during an observation period of about one year.

The first ¹³C NMR imaging method suitable for rotating solids is demonstrated and is shown to allow high-resolution ( approximately=100 mu m) accurate images to be obtained. Line narrowing is achieved by a combination of magic angle sample spinning (MAS), high-power proton decoupling and deconvolution. The small homogeneous linewidth, high-Q probes and narrow-band receivers associated with ¹³C NMR compensate to a large extent for the low natural abundance and small gyromagnetic ratio of ¹³C. The resolution and sensitivity of ¹³C imaging, which is generally simpler to perform, are comparable to those of multiple pulse ¹H imaging. Limitations of the method due to the residual broadening from off-resonance proton decoupling and interference of the MAS averaging of the chemical shift anisotropy by modulated magnetic field gradients are discussed.

A system for the measurement of the Fourier components of low-level electrical signal is presented. The system has been applied to the measurement of the harmonics of the dynamic hysteresis loop of an amorphous material, finding a good correlation between the hysteresis loop obtained by conventional methods and the one reconstructed from the harmonics measurement. The theoretical limit of the system sensibility in magnetic flux measurement, assuming that the noise from the sense coil is sufficiently small to allow the most sensitive range of the lock-in amplifier used, is 1 nWb at 20 Hz.

A simple device to generate a stream of uniform sized liquid droplets is described. The device produces droplets in a range between 50 and 300 mu m in diameter. Inexpensive and easy-to-make glass capillaries are utilised to produce the liquid jet. Measurement of inter-drop separation with an optical microscope is used to monitor the size of the droplets in situ.