Table of contents

The basic techniques used in high-speed photography (i.e. cine, framing and streak photography) are briefly discussed and the various instrumental arrangements mentioned (i.e. moving film, rotating drum, rotating mirror, image converter, flash, etc.). Recent developments in image converters have led to cameras capable of resolving times of the order of 10^-12s, some versions having sensitivity in the soft X-ray region of the spectrum. Electronic tubes incorporating microchannel plates have been used as intensifiers in picosecond streak cameras, and as high-gain shutters for single-frame photography. Holographic methods have been adopted in the design of high-speed camera systems for detecting small movements such as deformation of plates on impact, and vibration studies. Electronic methods are being developed for the handling of the information produced by high-speed cameras, some systems dispensing with the photographic process entirely.

An improved jet thinning device is described which is a modification of an apparatus due to Taylor and Watkins (1969). Difficulties encountered with the original apparatus in obtaining foils with symmetric profiles are overcome to a considerable degree by incorporating a rotating specimen holder. The apparatus has been successfully used to thin heavily doped hot-pressed silicon-germanium alloys. Preliminary examination of foils of these materials by transmission electron microscopy indicates that microstructures present are unlikely to make more than a minor contribution to the reported reduction in thermal conductivity of fine-grained hot-pressed materials compared to their single-crystal counterparts.

A comparatively inexpensive mercury-pool tilt gauge has been developed which is particularly suitable for permanent emplacement in arrays. It may be read with a portable autocollimator to an accuracy of +or-0.4" (+or-2 mu rad). It may be employed in such diverse fields as engineering metrology, the monitoring of civil engineering structures and the prediction of volcanic eruptions (Unesco 1971). The principle is that a mercury pool provides a reflective horizontal datum, so that a superimposed mirror coupled to the surrounding bedrock discloses any relative angular displacement when both are viewed simultaneously with a vertical autocollimator. This measurement is independent of the exact placing of the autocollimator.

It has been found that the combination of a 12 kW rotating-anode X-ray source and a curved LiF dispersing crystal provides 10³-10⁴ times more photon intensity for extended X-ray absorption fine structure (EXAFS) experiments than the combination of a 1 kW sealed tube and a flat LiF crystal used previously. Photon intensities of 5*10⁷ s^-1 in a 10 eV bandpass at 10 keV allow EXAFS spectra to be obtained in a few minutes. Intensities of 3*10⁶ photons s^-1 can be obtained with nearly 100% polarisation.

The construction of a simple photoelectron spectrometer for the study of molecular ionisation potentials is described. It has operated routinely in a teaching laboratory for five years with little maintenance. It is basically a slotted-grid retarding-potential analyser with a helium source and an inexpensive transistorised electrometer. A resolution of 25 meV (FWHM) can be obtained on the argon doublet and this is sufficient to resolve vibrational structure in the photoionised states of oxygen, nitrogen, hydrogen, deuterium, etc. The spectra reveal the electronic structure of atoms and molecules in a direct way making the orbital shell structure immediately evident to the student.

A high-voltage pulse generator is described which produces 20 kV rectangular pulses having 10 ns rise and fall times, a duration from 30 ns up to milliseconds and repetition rates up to 50 pulses s^-1. The main advantages of the device over customary circuits are low jitter, small triggering power and large range of pulse width.

This note presents the design of a simple glow discharge array detector based on a hybrid series/parallel interconnection of nine commercially available glow lamps and to describe a series of experiments performed with it. The study reported was performed at 70 GHz. It is shown that low-cost glow discharge detectors can be combined with low-cost integrated circuit components to synthesise a millimetre wave array detector possessing an enhanced signal-to-noise ratio.

A simple apparatus is described which makes use of quartz crystal oscillator and a digital frequency meter to measure thicknesses of vacuum-deposited films. Experimental results are presented which show that film thicknesses as measured with this apparatus proved more accurate than those measured with a commercial film thickness monitor. Such an apparatus is economically attractive and its versatility gives it many useful advantages not present with commercial monitors.

A new type of detector for molecular beams is described, in which the sensitive element is a superconducting tin or indium film at the transition temperature. The construction and calibration procedures for the bolometers are reported. The devices have a time constant of 1 mu s and a maximum sensitivity of about 10⁸ molecules s^-1 Hz^-1/2 corresponding to an electrical noise equivalent power of 2*10^-12 W Hz^-1/2.

The use of velocity modulation techniques to enhance signal-to-noise ratios in time-of-flight analysis of molecular beam scattering is discussed. The design, construction and performance of such a device for use in experiments with charge-exchange beams are described.

A null detector for use with audiofrequency capacitance bridges is described. A superconducting inductor is used in a matching network at the input of the detector. Capacitive feedback in the preamplifier of the detector determines the bandwidth. For a bridge with an output capacitance of 1 nF operating at a frequency of 1592 Hz ( omega =10⁴ rad s^-1), the noise contribution from the detector is negligible compared with the noise contributed by the output conductance of the bridge (about 1.5 nS).

A laser anemometer operating in the fringe mode has been designed to measure the velocity and size of droplets with diameters between 0.1 and 1.0 mm. The time for the droplet to cross the optical axis is measured and correlated with simultaneous measurement of the droplet velocity to give the droplet size. The system is sensitive to the direction of movement and the size measurement is restricted to the cross-sectional diameter of the droplet. The evaluation was limited to simple droplet flows but an automated system is applicable to sprays of large droplets.

A photon correlation system is described which has successfully been employed to measure pulsating air flows in glass tubes down to 5 mm in diameter. A sampled version of the signal from a laser Doppler optical arrangement has been used to construct velocity profiles at different phase positions in fully reversing flows, and these agree well with theoretical predictions. Peak Reynolds numbers were of the order of 100 and the frequency range was 0.25-4.88 Hz, corresponding to flow parameters in the physiological range.

Resistance heating may be used to release the tension in a highly stressed wire and thus produce small displacements. This principle has been employed in a device for tuning the length of a fused-silica etalon. Force changes of over 540 N were produced with only 5 W of control power required. A servo length-control system incorporating this driving element operated with an 80 ms response time.

The line profile due to diffractometer instrumental conditions was obtained from the measured line profile of a standard specimen by eliminating the spectral broadening, applying a model for the wavelength distribution. Under common experimental conditions, it was found that for 2 theta >50 degrees the spectral broadening is dominant in the line profile, and that for the larger 2 theta values for small values of the harmonic number the Fourier coefficients corresponding to the broadening caused by the instrumental conditions may be assumed to be independent of 2 theta .

The authors describe a system suitable for the measurement of electron temperatures in the range 0.1-10 eV and densities of the order of 10¹⁵ m^-3, consisting of a computer-controlled data acquisition system with off-line data analysis. For the latter stage the authors have developed an algorithm based on curve-fitting techniques to extract the required information in the presence of significant departures from the expected hyperbolic tangent form for the probe characteristic, including in particular the non-zero slope and curvature of the 'saturation' parts of the curve which occur when the probe size is comparable to the Debye length. The authors have tested the system by comparing the results with temperatures obtained by other methods, and have used it in a survey of the temperature and density distributions in the UMIST quadrupole.

The use of an array of loudspeaker elements for an acoustic sounder antenna is discussed. The effect of variations between the phase and amplitude of individual elements in the array is investigated and measurements are compared with the predicted radiation patterns for both a 6*6 square array and a 2*12 rectangular array of re-entrant horn loudspeakers.

A jet polishing apparatus is described which is suited for the preparation of thin foils for electron microscopy for specimens of non-standard geometry. This is achieved using an interchangeable system of locating glass components designed to provide optimum conditions for individual requirements. Thin foils from many different materials have been successfully prepared using this technique.

A new, simple and accurate active bridge for measuring all the FET parameters at low frequencies is proposed. The transconductance g_m, the drain conductance g_d and the gate conductance g_g are the low-frequency dynamic parameters. These are measured at and around the quiescent point. The role of these parameters for the analysis and design of circuits incorporating FETs is so important that they should be measured accurately; such measurement is the subject of this paper. A short error analysis for all the parameters has also been included to establish the superiority of the proposed method over the existing methods.

It is shown that the detector counting losses with synchrotron radiation from storage rings operated in a multi-bunch mode are little greater than with steady sources. This is not necessarily true with single-bunch storage rings. In many experiments counting rates will be limited by the detector capabilities rather than by the available flux.

Ionography can replace conventional film autoradiography in the detection of radioactive spots on thin-layer chromatograms. The sensitivity of autoionography has been greatly increased by the use of thick charge receptors instead of the thin imaging foils used hitherto, and also, for some radionuclides, by the use of higher gas pressure. The sensitivity of the method is now such that the following activities of three commonly used isotopes can be imaged in 24 h with a resolution of at least 2 line pairs mm^-1: for ³H, 4 nCi cm^-2 (185 Bq cm^-2); for ¹⁴C, 1 nCi cm^-2 (37 Bq cm^-2); and for ³²P, 0.05 nCi cm^-2 (1.85 Bq cm^-2).

An apparatus is described which was used to test dynamically the response of X-configuration hot-wire anemometer probes to enable a comparison with conventional static calibration to be made. It was found that the static calibration gave acceptable accuracy and that this accuracy was maintained to surprisingly high levels of the velocity fluctuation. The usefulness of such a device for directly testing a measurement system involving hot-wire anemometry is indicated.

An analysis is made of the contribution of the radial deformation and viscous effect to the effective area of piston-cylinder assemblies used as precision pressure generators. These effects are also examined using varied experimental techniques at 40, 80, 120 and 160 kPa for different piston-cylinder geometries and materials of construction. Significant correlation is obtained between the theoretical model and the experimental data.

A new comparator is described which makes use of the Tomkins and Fred setting method with direct viewing on a screen. This apparatus allows an accurate setting to be made not only on well resolved spectrogram lines but also on those which are diffuse or of low contrast.

A temperature controller is described, capable of maintaining the temperature of a properly constructed thermostat constant to within +or-5 mu K for an hour and 40 mu K for a week in the range from about 280 to 320K. It uses a thermistor as a sensing element in conjunction with a simple AC Wheatstone bridge. The electronic circuits of the controller, consisting of a lock-in amplifier, a proportional, derivative and integral regulator and a power stage, are built of low-cost, commonly available components. An extension of the temperature range of application is straightforward, but will lead to reduced accuracy.

A precision regulator for annealing of polarised-electron field emitters without thermal overshoot is described. It is implemented by means of a microprocessor board which is used in the same experiment as a multichannel scaler for measurement and differentiation of retarding-field electron energy distributions. The same microprocessor board can be equipped with several counter inputs for setting up a multiple-input multichannel scaler with which energy-selective electron spin polarisation measurements can be performed.

Fluorescence polarisation techniques are usually employed in the investigation of either orientation in frozen media or molecular mobility in isotropic media. The theory of fluorescence polarisation has been recently extended by the authors to the case where both orientation and mobility are present. An apparatus is described which permits simultaneous determination of orientation and mobility in a uniaxial distribution of moving molecules. It is well studied to the study of the rheological behaviour of polymers under stretching.

This letter presents basic results obtained with a single crystal of YAG:Ce³⁺ of 25 mm diameter and 60 mm high from which scintillators of arbitrary shape and size can be ground. Single crystals of this size were prepared by growth from a melt in an atmosphere comprising a special gas mixture and at well correlated crystal growth rates and solid-liquid interface temperature gradients. They contain about 1% of Ce³⁺ acting as the activator in the garnet crystal lattice.

Hughes (1972) proposed a 'plasma diode' technique to protect high-power laser systems from back-reflected light when magneto- and electro-optical isolators cannot be used for technical or economic reasons, as in far-infrared lasers or lasers with a beam diameter exceeding about 20 cm. The system uses the plasma itself to block the back-reflected light and employs a minimum of refracting and reflecting optics. The authors report the successful operation of the plasma diode device with relatively long-duration (nano-seconds) laser pulses.

Detection of gravitational radiation by some form of Michelson interferometer illuminated by a laser depends on observing the small relative displacements or forces which would be induced in test masses by a gravitational wave. The uncertainty principle would appear to set one limit to the sensitivity for detection of such displacements by a linear position-sensing system such as an optical interferometer. The authors discuss this limit, and also show how one method of treating photon statistics and photon recoil effects yields a similar limit. This is done in the spirit of the 'Heisenberg microscope'.