Table of contents

The decision to make SI mandatory in Journal of Physics E: Scientific Instruments marks the final phase of the inexorable progression from the babel of discordant units to the clear notes of a single and yet universal system. The author gives a personal commentary demonstrating the great benefits which a consistent and committed use of SI can bestow on scientists and engineers alike.

A computer-controlled, fully automated beam-scanning system for use in colliding beams experiments or for investigation of the behaviour of ion optical systems is described in detail. The construction details of the shutter mechanism together with the critical points in its design are presented. Sample beam profile data are given in the form of contour plots.

A sensitive torque magnetometer for use in a superconducting magnet is described. A feedback mechanism is used to keep the sensitivity of the magnetometer independent of sample rotation and magnetic field. Sample rotation rate is controlled with precise readout of position through +or-100 degrees . A positional angle modulation technique makes the magnetometer an ideal tool for studies of induced torque. This technique eliminates static background torques and de Haas-van Alphen torque with the proper choice of modulation amplitude. Induced torque sensitivity is 100 times larger than that obtained by direct sample or magnet rotation. The field dependence of the induced torque at any sample position can be obtained directly in a single field sweep. Torques between 10^-9 and 10^-3 N m can be measured with a compliance of 180 rad N^-1 m^-1. The magnetometer is also useful for detecting the de Haas-van Alphen effect.

The design of a simple modulator for microwave spectroscopy is presented. Half-sine wave modulation is used instead of the more usual square wave. The Stark lobes nearly vanish and do not perturb the zero-field transitions. This type of modulation enables one to detect more easily small lines in dense spectra or nearby intense lines. Using high modulation frequencies, extremely high fields can be obtained at lower cost and without observing any spurious pickup. For analytical work in microwave spectroscopy this type of modulation seems to be very convenient when line areas are measured.

The resonance lines from a helium microwave source are quantitatively measured from the photoelectron spectra of argon. The lines are shown in the example of the photoelectron spectroscopy of N₂O to cause difficulty in the identification of the onset of the third electronic band.

A variable coupling to a microwave cavity, achieved by rotating the waveguide with respect to the cavity, is described. The coupling device is sufficiently solid to avoid microphonics, it is easily remotely controlled and has a large tuning range.

A simple, inexpensive, solid state phase sensitive detector system designed for wide-line NMR and ESR spectroscopy is described. Its performance compared favourably with those of phase sensitive detector (PSD) circuits available in the literature. The input dynamic range is better than 90 dB over the frequency range 20 Hz-1 MHz.

The construction is described of a sealed crucible viscometer for studies of corrosive volatile liquids. The construction utilizes only platinum and alumina and is capable of operation at temperatures as high as 1500 degrees C. Its application is reported to PbO/PbF₂-based solvents and Y₃Al₅O₁₂ solutions.

The mass-to-charge ratio of an ion can be determined from the measurement of its flight time in an inhomogeneous, oscillatory electric field. The governing equation of motion is the Mathieu equation. The principle of operation of this novel mass spectrometer is described and results of computer calculations of the flight time and resolution are reported. An experimental apparatus and results demonstrating the feasibility of this mass spectrometer principle are described.

The system drives the tilt coils of a transmission electron microscope in order to bring each spot in the diffraction pattern from a single crystal in turn onto a central fixed scintillator-photomultiplier detector. The intensity of each spot is measured by integrating the photomultiplier current for a known time. The digitized intensity is then stored in a memory and may be displayed on an oscilloscope or punched out on paper tape for computer processing. Among the facilities incorporated are data accumulation with overwriting of previous data or with addition to or subtraction from previous data, and independent rotation and gain control of the two directions of scan.

An efficient system for the collection and analysis of cathodoluminescence (CL) excited by the electron beam of a scanning electron microscope has been developed, employing an ellipsoidal mirror with its major axis parallel to the beam direction, 45 degrees plane mirror, fibre optic light guide and grating spectrometer. The optical transfer efficiency from sample to detector is 5% at 500 nm. Spectra from areas a few micrometres across can be recorded using beam currents as low as 1 nA with a spectral resolution of 1 nm. Monochromatic CL micrographs can be displayed on the screen. Some applications of the instrument in the field of compound semiconductors are illustrated.

Details are given of an atmospheric acoustic sounder which can be used in both a rural area and a noisy town environment. The instrument has been used for the measurement of various parameters of the turbulent boundary layer including the temperature and velocity structure parameters C_T² and C_v² as well as vertical wind speeds. A summary of some of the results obtained using this instrument is presented.

Apparatus for the measurement of thermoluminescence is described which generates glow curves with an overall reproducibility of +or-5%. Particular attention has been given to the design of a controller capable of accurately reproducing a chosen linear heating rate (0.1-99.9 degrees C s^-1) up to a predetermined final temperature (ambient to 990 degrees C). A manually operated 'hold' facility for intermediate temperatures is also provided. The construction of the light-measuring system and checks on its stability, sensitivity and linear response to very weak sources are also described. The apparatus was designed for the study of linear samples and meteorites.

A wavelength-modulated spectrometer usable for reflectivity measurements between 150 nm and 900 nm is described. The chopped double-beam, single-detector system measures conventional and derivative spectra simultaneously. The cancellation of spurious derivative signals due to the modulated incident light is performed by an electronic servo-loop using multiplier modules. The direct and modulated reflectance spectra of cubic ZnS between 165 nm and 360 nm are given.

A general method is presented to study the response function (first harmonic) of velocity analysers to an arbitrary energy distribution N(E), as occurs in Auger electron spectrometry. The method is based upon finding the response to a delta function and convoluting the result with N(E). The response function has been numerically calculated for a Gaussian energy distribution which is analysed by a typical cylindrical mirror analyser. The distortions caused by the analyser itself and the technique of modulation have been separated. It has been proved that, depending on the energy at which the Gaussian is centred and on its halfwidth, there exists an optimum amplitude of modulation.

The sample cell system described built principally to study liquid crystals in a small-angle X-ray scattering Bonse-Hart diffractometer, is capable of temperature control to better than +or-0.001 degrees C in the temperature range 25-150 degrees C. With slight changes, it can be adapted to almost any X-ray scattering experiment, and its temperature range of use can be raised hundreds of degrees higher.

To measure high-voltage fluctuations in the frequency range DC to some 100 Hz, both the resistive and capacitive measuring methods are necessary. However, it is shown that in many cases the capacitive measurement of slow high-voltage fluctuations leads to good results.

A Thermo Systems Incorporated 1080 vector anemometer was used to map the general flow pattern of a complicated laboratory model of a tornado. Three-dimensional velocity vectors were measured with the aid of a low-pass filter for smoothing the fluctuating signal due to the inherent flow instability. The resulting pattern was in good agreement with visual observations (motion picture) of this laboratory model. The split film anemometer with its direction-finding capacity proved to be a useful instrument for this purpose, although the detailed flow structure was extremely difficult to obtain, owing to the application of a signal averaging technique. Sources of occasional error in determining the flow direction in association with this instrument are discussed.

An apparatus for studying the physical processes of secondary ion emission from ion-irradiated targets is described. The system uses a spherical electrostatic energy analyser and a quadrupole mass spectrometer both operating at fixed pass energy. Energy scanning is achieved using a retarding/accelerating field system. The apparatus is used for the study of the spatial and energy distributions of secondary ions and consequently its design parameters differ from those of a secondary ion apparatus intended solely for mass spectrometry studies. The system has an angular resolution of less than 1 degrees , an energy window Delta E approximately=1 eV, a mass resolution of 60 and optimum signal sensitivity of approximately 10^-8 counts per primary ion. Details of the design, analysis and testing of the system are presented.

An automatic short-time pulsed probe plasma analyser is described which has been developed for the investigation of concentric non-equilibrium plasmas with unidirectional electron and ion flow in an ion source with high emission density. Besides plasma potential and ion saturation current the electron energy distribution can be measured up to values of 300 eV and simultaneously integrated to obtain the electron density. These four parameters determined serially in a total of less than 2s at 46 different locations in the plasma are stored in a recirculating shift register memory and displayed on an oscilloscope for further analysis. Because of the short measuring time (compared to the depletion time of the higher energy electrons) distortion-free measurements of widespread electron energy distributions or high resolution measurements of the same are possible. The device has also been applied to the determination of transformation energies of plasma chemical reactions.

The excitation of a low-energy ground state helium beam to its metastable states by electron impact is analysed. It is shown that the narrowest velocity distribution for the resulting metastable helium beam is obtained by directing the helium and electron beams parallel or antiparallel. A source of metastable helium atoms was constructed according to this analysis which produced a beam of 3*10¹⁴ metastable atoms/s sr with a velocity resolution of 3% FWHM for a room-temperature beam (E=66 meV). A possible source of errors in time-of-flight experiments with metastable atoms is pointed out.

The recent introduction of bright light emitting diodes (LEDs) has made possible a simple but effective method of stroboscopic illumination. This capacity is used to observe the propagation of 5 MHz shear waves in a block of fused quartz, using an LED conducting about 5 A for durations of the order of 50 ns every 500 mu s, with the junction capacitance tuned out by a parallel inductor chosen to resonate at 5 MHz; TTL digital control is used throughout, except for a 35 V LED driver stage. There is sufficient light intensity for the eye to view the stress birefringence associated with the high-frequency sound wave. Possible applications include the non-destructive testing of transparent materials and the quality control of ultrasonic transducers.

The use of laser speckles for the measurement of out of plane tilts of diffuse objects has been discussed by Tiziani (1972) and Archbold and Ennos (1972). This method may be extended to the measurement of large tilt angles by recording the linear fringes produced on a fine grain film. This record can be considered as a diffraction grating, and when it is illuminated with a plane wave a lens placed behind the record displays diffraction orders in its back focal plane. Expressions are given for the displacement of these diffraction orders from the origin, and for the upper limit to the tilt angle that can be measured by the technique. The results are presented of an experiment to measure a 5 degrees tilt of an aluminium sheet acting as a fine grain diffuser.

The fact that certain organic compounds added to inorganic bleach baths can cause acceleration and deceleration effects is discussed with reference to the acceleration of ferric and cupric nitrate by the dyes phenosafranine and methylene blue. In this process the ionic migration of the silver of the emulsion is reduced by two constraints: the reduced mobility due to the presence of the large dye cations in the neighbourhood; and the shortened ionic lifetime before precipitation of the halide due to the influence of the local anionic cloud. The image-sharpening effect of these processes is just what is required in an image where resolution is a prime requisite. Some technical aspects of this acceleration are examined.