Table of contents

This review discusses the role of high-level languages and real-time operating systems when minicomputers are used in the field of scientific instrumentation. Comparative information is given on the advantages and disadvantages of the main high-level languages currently in use in the scientific environment. Information on high-level languages and real-time operating system facilities available on current minicomputers was obtained by sending a questionnaire to all major suppliers in the United Kingdom. To help to give a proper overview of the role of high-level languages and real-time operating systems, sections have been included in the paper on interrupt systems, benchmarks (speed tests), emulators, certain hardware facilities, instrumentation which already utilises minicomputers, diagnostic for and debugging of real-time programs, user groups, program packages, job control languages, interfacing, computer peripherals and microprocessors.

A method is described which makes full use of the data gathered in measuring the elastic constants and internal friction of small samples undergoing free decay. A Fourier transform approach is employed which first determines accurately the period and starting phase of the free decay and checks the purity of the signal. This information is then used along with the original data to determine the internal friction of the sample.

Describes an automatic apparatus for plotting internal friction Q^-1 and sample resonant frequency as functions of strain amplitude. Q^-1 is measured from the ratio of driving force to strain amplitude, while the sample is held at resonance by a phase-locked loop and the strain amplitude is automatically varied following a chosen function of time. This method allows continuous Q^-1 measurement, while an appropriate choice of the amplitude variation rate ensures that the measure Q^-1 corresponds to a definite strain amplitude rather than being averaged over an amplitude interval as is the case with other techniques. The system incorporates a resonance apparatus which employs an electrostatic drive without DC bias, but any type of resonance apparatus can be used with minor adjustments. The ranges of Q^-1, strain amplitude and operating frequency are those of the resonance apparatus employed.

Discusses the time resolution of p-i-n photodiodes applied as electron detectors. The rise time was found to be of the order of 1 ns, which is equal to that in the case of photon detection. However, it appears that in electron detection the initially fast decay turns over in an exponential decay with a time constant of about 30 ns. A simple algorithm is presented that corrects the recorded waveform for the effects of this tail.

A device for separating and reuniting the signal and idler of a LiNbO₃ optical parametric oscillator (OPO) with orthogonal polarisations is described. This uses specially constructed edge coatings and the optical activity of crystal quartz which has been measured in the near infrared using the OPO. Initial experiments have indicated an increase of 2.3 times in the energy of the mixed beam in CdSe compared with the energy when the crystal is set at 45 degrees to the direction of the polarisations.

A simple analysis of the modulation excitation spectrophotometer is given and a simple method of obtaining lifetimes of transients derived.

A new method of measuring the absolute direction of the Earth's magnetic field has been developed, comprising a cylinder with a radial hole spinning about its axis on air bearings. The device acts like a single-turn coil and a misalignment between the spin axis and the direction of total field causes currents to flow in the cylinder which are detected by static quadrature coils fixed to the instrument frame. The signals are phase-sensitively rectified and fed back to small Helmholtz coils to cancel the small fields producing the misalignment. When combined with an absolute scalar instrument, the vector magnetometer provides complete and continuous absolute vector information, and could find application as a standard observatory instrument.

The two-photomultiplier method of studying scintillator decay has been adapted to measure over the time range from 0.1 mu s to 3 ms. Results are given for the most commonly used inorganic scintillators with both alpha and gamma excitation. It is found that the decay is, in most cases, better described by a power law than by a series of exponentials. The results for caesium iodide are analysed to derive the optimum filter for use in pulse shape discrimination. Attention is drawn to the influence of the decay behaviour on the reported measurements of scintillator efficiency.

A spectrometer system for nuclear quadrupole double resonance by level crossing (DRLC) has been built which is controlled by a programmable desk top calculator equipped with a tape cassette and a thermal printer. A sketch of the gross features of the spectrometer and a detailed description of the interfacing circuitry are presented.

Describes an instrument which can be used to measure the neutral-particle flux from a plasma over the energy range 200 eV to 30 keV. This wide range makes the device especially useful for plasmas where neutral injection heating may be employed. It has been used for measuring both the ion temperature and the high-energy spectrum due to the injection of high-power neutral beams into the DITE (Divertor Injection Tokamak Experiment) Tokamak.

A digital image-processing system based on a minicomputer has been developed, which is especially suitable for man-machine conversational image processing. This system features parallel connections of the main memory of a computer with a central processor unit, a detector and a cathode ray tube monitor by the direct memory access channel. By the time-shared operation of memory access, this system provides a human observer with not only an image after processing but also the image in the course of processing or detection, without flicker. Applicability of this system to man-machine conversational image processing is demonstrated through restoration of a defocused image and the extraction of subtle structures within an X-ray photographic image.

A ratiometric photometer is described of simple construction and original design. The instrument includes a novel photoelectronic divider system which is described in full. Data are presented of some representative measurements made both in transmission and in reflection of thin-film and bulk specimens.

A longitudinal strain modulation system, consisting of a composite transducer, amplitude transformer and a resonator with the sample under investigation has been designed for use in ESR and optical spectroscopy. The method of strain calibration is described. Some applications of such a modulator are mentioned.

The basic theory of both the simple rod calorimeter and the alternative pedestal form is given, including an analysis of the transient behaviour for each. The possible exploitation of the low c-direction thermal conductivity of pyrolytic graphite in such calorimeters is discussed, and a proposed design (of the pedestal type) is described in detail. The proposed calorimeter is of a basic probe format and would have as its major application the measurement of dose in high-level high-energy photon and electron fields as used in radiation processing.

A description is given of equipment for the measurement of the Kerr effect in water and other relatively highly conducting media. The equipment uses 2 mu s field pulses up to 8 MV m^-1 in amplitude and is sufficiently sensitive to measure the smallest Kerr constants such as that of carbon tetrachloride. Illustrative results are presented for water.

Describes a circuit which uses a 3554 Burr-Brown OA which has a 1.7 GHz gain-bandwidth product, full differential input and an input impedance of 10¹¹ Omega .