Table of contents

A simple and easily constructed spectrometer is described by which it is possible to measure the electrical mobilities of submicrometre radioactive aerosol particles with an estimated absolute accuracy to ±4% and a relative accuracy to ±0·5%. The resolution of the instrument is 3% in mobility.

A conductivity cell incorporating the impingement principle suggested by Nash has been designed to facilitate the continuous measurement of atmospheric sulphur dioxide. The instrument based on this cell is provided with several measuring ranges which can be selected to give full scale deflection from 0·2 to 5 p.p.m. sulphur dioxide.

A crossed molecular beam apparatus for the measurement of differential scattering cross sections has been constructed. The effective angular resolution is better than 0·05° and permits the observation in the laboratory of quantum undulations with a period of the order of 0·2°. For sodium or potassium in a clean system the signal standard deviation is 3 counts per second permitting neutral fluxes of 1 atom per second into the detector to be estimated in a reasonable integrating time. The associated data capture and deconvolution procedures are also described.

Laboratory measurements conducted on 100 kHz piezoelectric transducers mounted on a diaphragm similar to the micrometeorite sensors flown on Vanguard III, Explorer VIII, Mariner II and IV are described, which show that the stresses induced at impact are coupled to the piezoelectric sensor predominantly by a bending mode in the diaphragm, rather than by a longitudinal compression radiating from the impact region. Particles impacting at velocities ranging from 10 cm s⁻¹ to 6 km s⁻¹ induce similar vibration modes. The momentum imparted to the diaphragm in this mode, resolved along a normal to the surface, will equal the sum of the momenta of the impacting particle and of the rebounded particle (or ejected matter at hypervelocities), and a piezoelectric crystal mounted with its sensitive axis normal to the surface will develop a signal proportional to the total momentum exchange at impact. Such a system will, therefore, bear resemblance to a ballistic device; the fraction of this momentum which falls within the frequency range of the sensing crystal may, however, be affected by the area of contact and by the contact time of the particle. It is shown that the contact time of small beads can lead to significant errors of calibration.

Data from a combined gas chromatograph-mass spectrometer have been obtained and recorded on-line to an IBM 1800 computer, and also on an off-line digital magnetic tape recorder for later processing of the data by the computer. Incremental and continuous modes of recording were used and in all cases a fast electronic mass marker established the mass scale. Several hundreds of mass spectra were consecutively recorded. Computer programs have been developed to evaluate the mass spectrometric data.

This article describes a comparison of various resonators especially designed to be used for electronic paramagnetic resonance at metre wavelengths and low d.c. field. A comparison with classical quarter wave resonators shows that a similar but capacitively loaded resonant structure provides a substantial improvement in spectrometer sensitivity. A method for the measurement of the product of the filling factor and quality factor ηQ is described and used for a comparison of various types of resonators at 210 MHz.

The performance of a fast image intensifier system is studied for very short exposure times, below 1 ns for event controlled exposure and at 10 ns with a gating pulse. It is concluded that the tube will operate satisfactorily in the gated mode down to 1 ns subject to the availability of suitable gating pulses. The tube is also a good photomultiplier.

A procedure is described by which the focal properties of a three-element lens can be determined in terms of the properties of two-element lenses. Examples are given in some detail of the design of lenses to meet specific requirements and a graph is presented which can be used to design a lens of unit magnification which will work over a specified extreme voltage ratio in the range 6·25:1 to 170:1. The range of applicability of the method is discussed and a comparison made with measurements by Imhof and Read where only a limited agreement is expected. This comparison supports both the method and its limitations.

The design and construction of a simple electron probe microanalyser capable of less than 10 μm resolution is described. Focusing of the electron beam is achieved by a single einzel electrostatic lens. Analysis of the emitted X-ray is accomplished with an air-path two-circle goniometer, analysing crystal, and xenon filled proportional detector. A light optical viewing microscope is provided for positioning the specimen.

The performance characteristic of the probe in the analysis of metal diffusion couples is included.

Directionally sensitive detectors have been used in the scanning electron microscope to reveal additional detail due to deflection or non-uniformity of the spatial emission distribution of the secondaries which form the electron picture of the surface under examination. Deflection may occur as a result of electric or magnetic fields above the surface; also the emission characteristic may be anisotropic, or modified in shape and direction by local surface structure. These effects all occur in addition to the principal source of contrast in the scanning electron microscope, i.e. changes of secondary emission coefficient. The directional content of contrast is normally small, but the system discussed causes considerable enhancement of these effects. Results have the appearance of `shading' of surface detail, revealing more clearly the nature of shallow undulations, with a three-dimensional effect similar to that obtainable by optical microscopy with side illumination. Comparative results are presented which indicate the advantages to be gained for examination of small surface detail. By appropriate adjustment of electrostatic bias on electrodes, the detector system can provide magnetic contrast, potential contrast due to changes in surface electric potential, electric contrast from horizontal electric fields and improved sensitivity to surface topography. To a considerable extent these can be separately identified by observation under several different detector field configurations.

A regenerative drive system is described for kilohertz acoustic measurements in alkali halide crystals. In the system field effect transistors are used as gain control elements to keep the strain-amplitude of mechanical vibrations constant during experiments in which internal friction and modulus are changing. Discussion is given of the main features of the design of the equipment, its testing and calibration and its application to experiments involving effects of nuclear radiation on alkali halide crystals.

An inexpensive hydropneumatically operated crystal puller is described. The basic apparatus provides infinitely variable pulling rates up to over 100 mm h⁻¹. At rates over 2 mm h⁻¹, the short term variations are less than 3% and long term changes are less than 5% per hour. The rotation rate is smoothly variable from zero to about 140 rev min⁻¹ with a drift of less than 5% per hour at any given speed. The apparatus has been used with a variety of growth assemblies to grow crystals of materials with melting points in the range 270-2000°C.

In order to generate the maximum power from pulse modulated Gunn oscillators it is necessary to use bias voltages which approach the avalanche breakdown voltage of the device. A description is given of two transistor pulse generators which avoid damage to the oscillator by providing a current or charge limit respectively on the avalanche current when breakdown occurs.

A method for linearizing thermocouple output is proposed with particular reference to measurements of small temperature differences over a large range of mean temperatures from − 100 to +200°C. The linearization is obtained by using composite sensors including copper or platinum resistors which, added to an appropriate external resistance, provide a linear current or voltage output. The linearizing resistors do not need to be at the exact temperature of the junctions. The linearity attained is to better than ±0·1 degK within a span of 150 degK for copper-constantan or Chromel-constantan thermocouples.

It is suggested that many binary or pseudo-binary gas mixtures may be analysed by measuring their acoustic velocities. The construction and operation of an ultrasonic interferometer and its application to the analysis of gas mixtures are described, and a possible pulse method is discussed.

The low-frequency homodyne spectrum of the argon laser is known to contain a noise spectrum due to mode interactions, thus limiting the laser's use for low frequency Doppler shift measurements. Results are presented here for lasers of different constructions which show that under appropriate running conditions this noise spectrum may be suppressed. An anemometer based on the argon laser operating under optimum conditions has been developed, and results are presented of the heterodyne spectra from a fluid in both laminar and turbulent flow and the homodyne spectra of fluids in turbulent flow.

The paper describes a dilatometer which has been designed for the study of the kinetics of solid-liquid metal interaction. This apparatus can operate in a vacuum or at different atmospheres. The dimensional changes produced during the interaction and the temperatures of the furnace and the reacting specimen are automatically recorded.

An apparatus is described which enables a set of six masks to be repeatedly registered with a substrate in a high-vacuum environment with an accuracy to ±1 μm. Details are given of the mask manufacture, which involves preferential etching techniques to produce high definition patterns. An analysis is made of the registration errors to be expected.

Glass micropipette electrodes with extremely fine tips and high mechanical rigidity have been fabricated with a semi-automatic pipette-puller. The fabrication involves a two stage pull of a heated glass capillary held horizontally by a pair of non-slip clamps. Air is automatically blown from symmetrically located nozzles on to the softened portion of the capillary at the onset of the second pull. With this technique micropipettes with a relatively short taper and large cone angle at the very tip are produced, which not only possess high mechanical rigidity, but also a fineness at the tip (500 Å or less). A special advantage of the large cone angle at the tip is that such an electrode has a much lower electrical impedance than a conventional micropipette electrode with a comparable tip diameter. The size and shape of the micropipette can be easily altered to meet the specific need. The principle of differential vapour pressure has been utilized to fill the micropipettes with the desired electrolytes. A vibration technique for inserting a microelectrode into living cells is also described.

Changes in the photoelectric emission from a tungsten surface contaminated with small amounts of caesium have been used to measure surface concentrations of caesium in the range 5 × 10⁻⁴ to 10⁻² monolayers.

A coaxial cylinder viscometer for the study of non-Newtonian materials under conditions of continuous shearing at a constant stress is described. The rate of shear is controlled in such a way that the shearing stress is kept constant at a preset value. The apparent viscosity is inversely proportional to the motor speed. The stress can be varied between 100 and 800 dyn cm⁻²; at 400 dyn cm⁻² the viscosity range is 2-50 P. The accuracy is within a few per cent.

A 10 m span, tensioned-wire strain seismometer is described which has successfully recorded solid-tidal strains in Britain. Secular drift is within a few parts in 10⁸ per week and sensitivity exceeds 1 part in 10¹⁰. Needing only two-point support it can be installed in a few hours for immediate use. The cost is comparable to that of conventional seismometers and is considerably less than current types of strain meters; it can therefore be used on an extensive scale for geophysics research.

The accurate measurement of high emission rates of alpha radioactive sources has been neglected up to the present time. In order to resolve this difficulty a new 2π proportional counter was developed, capable of measurement up to at least 5×10⁵ alpha particles per second into 2π geometry. Careful attention was placed on the factors limiting counting speed, notably mechanical and electrical design of the counter and preamplifier circuitry. The choice of counting gas was also critical for high speed applications. The calibration of the counter was checked using a certified standard source from the Radiochemical Centre emitting 1·029×10⁵ alpha particles per minute. The measured emission rate of the source agreed to within ±0·1% of this figure.

An apparatus capable of identifying boiling regimes around a heated body cooling in a liquid is described. The principle of reaction forces is utilized in the device. The apparatus was used to identify the onset of transitional boiling around a heated sphere cooling in water.

Composite construction, with O-ring seals, can reduce the illegible region of a collinear manometer to about 1/8 of the length required by glass construction.

An apparatus is described which allows bulk densities of tapped powders to be determined in air, vacuum and in the presence of controlled pressures of various gases and vapours. Typical results are quoted.

The note describes a method for instantaneous measurement of the decay rate of vibrations by counting the number of cycles between two levels and displaying the result on a digital counter. The frequency range is 5 Hz to 25 kHz for logarithmic decrements in the range 0·005-0·150.

A cryostat is described which has been used for sample temperature control in a pulsed n.m.r. spectrometer in the range 78°K to room temperature. The temperature controller may be preset to the sample temperature required and the sample subsequently maintained at this temperature to better than 0·5 degK for long periods of time. The advantages of this method of temperature control over the more conventional gas-flow and controlled heat-leak methods are discussed.

A bridge network is described, which can attenuate bus-bar noise by factors ranging from 300 to 500 when making discharge measurements at very high voltages with an ERA discharge detector. Also it gives sufficient attenuation of noise from discharges on the guard ring of test samples, so that discharge measurements on samples of generator stator or motor coils with the ERA detector becomes possible.

The performance of the bridge network as a filter is independent of the bandwidth of the detector and hence it can be used with either model 2 or model 3 ERA detectors.

The construction and performance of a simple helium Dewar is described. A large apparatus space is achieved within the small outside dimensions by replacing the normal liquid nitrogen jacket by a conduction-cooled metal radiation shield.

Nous decrivons une cellule metallique, a joints d'or presentant un volume mort negligeable et permettant d'etudier par spectroscopie infrarouge la structure des complexes adsorbes jusqu'a des temperatures de l'ordre de 250 C.

Some of the problems involving the production of high efficiency laser mirror coatings are discussed. Gross scattering losses caused by dielectric particles becoming embedded in the multilayers present a major problem. An apparatus is described which was successfully used to reduce this effect to a very low level on one inch diameter, 23-layer mirrors.

A double-beam recording spectrodensitometer has been constructed to measure the optical density of dry agar electrophoregrammes. The measuring and reference beams are modulated with different frequencies. Two resonance amplifiers separate the signals. The electronic logarithmic recording is independent of the nonlinear characteristics of the valves.

A viewing probe for inspecting foam conditions is described, based on the critical reflection of light from a flat optical surface. It is intended for the inspection of conditions in distillation columns and other systems containing gas/liquid mixtures.

A device for simultaneously equalizing temperatures and greatly reducing temperature gradients in test furnaces has been developed. This device consists of a liquid-sodium filled furnace liner which eliminates the need for multiple zone furnaces for most applications.

This note describes the design and working of a regulated, reliable and compact electromagnetic powder dropper for flash evaporation, which does not require transmission of mechanical movement through vacuum seals.

An energy analyser is described for measuring the energy of the secondary electrons in the scanning electron microscope. It consists of a 63° deflection cylindrical analyser followed by an electron collimator. This is simpler than a mirror design reported previously and gives a higher transmission factor and less defocusing of the electron beam of the microscope. This analyser has been applied to measure point-to-point variations in surface potential with an accuracy to ±1 V.

A simple quenching circuit is described which reduces the dead time of Geiger-Müller counters by lowering the anode voltage immediately after the beginning of the discharge. The circuit delivers negative pulses with 300 V amplitude and 28 ns rise time. This extremely short rise time has not so far been achieved with similar circuits.

The ganging of silicon carbide disks for the slow speed multi-cutting of brittle semiconducting dice is described. With twelve 0·125 mm disks and spacing collars as required (e.g. 0·25 or 0·5 mm), one hundred and twenty one dice were produced in two cutting operations with an accuracy to better than 25 μm and minimal chipping. It is concluded that the process could be readily expanded to employ up to fifty disks and a yield of approximately 2400 dice and that the use of silicon carbide disks is suitable economically.

A simple, all solid-state, circuit is described which has produced a square wave with an amplitude of 1800 V and a frequency of 80 kHz in a capacitative load. The device is of application to Stark modulation in microwave and gas radical e.s.r. spectroscopy. It has certain advantages over previous systems in being more compact, providing an output which is automatically zero-based and also continuous over the range 5-1800 V, thus avoiding the need for capacitative division.

A simple circuit is described which closes a relay contact within a millisecond or so of the start of the first counter display period containing the initiating digit.

The problem of designing a holder for use with the ITT F4000 (or FW114) biplanar photocell is discussed together with the intrinsic properties of the photocell. The intrinsic photocell rise time combined with that of the simple holder described gives a 10-90% rise time of 280 ps. This is virtually as fast as previously published designs for this photocell but also gives over twice the current (up to 4 A into 125 Ω) for the same cathode current, thus increasing the useful dynamic range. The response of the photocell in its holder is combined with the response of a Tektronix type 519 cathode-ray oscilloscope to give an overall response and curves of true and observed pulse lengths which can be used to measure pulse lengths and peak powers for pulses down to 300 ps half-width.

The servo-operated piston burette system described records changes in gas volume of up to 50 ml at a constant pressure of up to 2 atm. The ready-made servo system of a standard potentiometer recorder is used both to drive the piston and to position the pen on the recorder chart. The sensing element is a strain-gauge pressure transducer. The apparatus may be adapted for recording change of pressure at constant volume.

The principle of a new type of Debye-Scherrer camera is described which is suitable for the Ross-filter technique or for the quantitative comparison of diffraction patterns (especially of non-crystalline samples). Arguments for the development of this camera and an example showing the accuracy are given.

An air cooling jacket was added to the newly developed fibre-optical displacement sensor (Fotonic sensor). This modified probe was successfully calibrated in a hot environment, up to 600°C, with a sensitivity of up to 20 mV per 0·001 in displacement.

A modified Ubbelohde viscometer with interchangeable capillaries is described. The design is considered to be superior to the standard Ubbelohde viscometer and its operation is further improved by incorporation of a photoelectric timing device.

The polarimeter instrument consists of three optical channels, two of which contain Glan Thompson type polarizing prisms oriented at 90° and 135° with respect to the vertical, while the third contains a neutral density filter of 50% transmission. Measurement of the three Stokes parameters I, Q and U of linearly polarized light are made by comparing the polarized beams with the unpolarized beam using an electromechanically driven beam selector wheel, fibre optics beam mixer, a single detector and associated electronics. Precision measurement of small differences between the signals from the different channels directly off the detector enables small degrees of polarization to be determined with higher accuracy compared with a different scheme of measurement described in an earlier instrument. Further details of the instrument and some test results are presented.

An efficient gas-circulating pump constructed of glass and Teflon is described. It derives from a simple design by Watson in which a reciprocating piston is actuated by external solenoids driven by a multivibrator circuit. Modifications to the piston heads and non-return valves have resulted in a circulating rate of 50-60 ml s⁻¹ for both oxygen and hydrogen, at pressures down to 10⁴ N m⁻² (0·1 atm).

An artificial daylight source which uses the filtered light of high pressure xenon lamps is described. Its spectrum approximates to the D6500 standard in the visible part of the spectrum with errors of −6·5, +3·3, −3·4, +0·8, +1·1, −0·1% respectively in the wavelength bands 400-455, 455-510, 510-540, 540-590, 590-620, 620-760 nm.

A device is described for recording changes in spectral composition with time, by exposure of successive linear elements of the spectrograph slit through a curved slot in a rotating shutter-disk. The shutter-disk is rotated synchronously with the cyclic variation of some parameter in the spectral source.