Table of contents

A relatively simple apparatus has been developed for the direct measurement of the intensities of low energy electron diffraction (LEED) beams from the surface of a single crystal target. The energy and angular distributions of all the electrons inelastically scattered or emitted from a single crystal or polycrystalline target surface, monitored by LEED, can also be measured in this apparatus. LEED and electron or ultraviolet light induced electron emission measurements may be observed over a solid angle of emission of 3 π st. The apparatus includes a service area, for preparing crystal surfaces under u.h.v. conditions, and manipulation devices, for transferring the specimen from the service area to the measuring area, and orienting its surface for a wide range of angles of incidence of the primary electron beam.

A rotating drum densitometer is used to evaluate x-ray diffraction films. The instrument scans a 12 cm × 12 cm precession photograph in 150 s at a 200 μm raster and records the intensity readings on magnetic tape at 256 grey levels. The densitometer response is judged to be linear to an optical density of 1·9 and is accurate enough to yield integrated intensity values with a reproducibility of 1%. We describe in some detail the rationale of the computer program used to determine these intensities.

A pulse fluorimeter is described which allows measurements of fluorescence decays in the range 1 ns to 1 μs. The system is built from a modified Hundley light source with 1 kHz repetition frequency and a commercially available sampling oscilloscope combined with a signal averager. The signal is digitized at 254 discrete time positions with a 10 bit resolution. Up to 256 scans can be summed and the data can be read out either analogue or on punched tape for digital processing. Both the shape of exitation pulse and the fluorescence decay curve are measured and individually corrected for spurious signals.

Measurements of the resolving power of examples of the NE421 (0·65 mm granular), NE905 (1·3 mm glass) and gadolinium (25 μm metal foil) intensifying screens used in thermal neutron radiography are presented. The observations were made on images of a gadolinium knife-edge object using a microdensitometer with a recently developed digitized output. This is described along with the image analysis techniques used as they may be useful in other fields.

Conventional unsharpness figures were obtained using two alternative measurement criteria which give somewhat different values; the popular method due to Klasens giving: NE421, approximately 1100 μm; NE905, approximately 450 μm; Gd foil, approximately 70 μm. The contrast transfer function of each screen in conjunction with Ilford HP3 film was also determined. The spatial frequencies at which the contrast of the image falls to 10% of that produced by an extended object of the same thickness are: NE421, 2·3±0·4 cycles mm⁻¹; NE905, 5·1±0·8 cycles mm⁻¹; Gd foil, 9·7±0·6 cycles mm⁻¹.

Finally the transfer functions of a series of experimental screens are presented together to demonstrate the value of the techniques used to component development.

An apparatus for accurate measurement of liquid densities, based on the second of two designs due to Beams and Clarke, is described. The sealed sample cell contains a glass float, which can be held magnetically in the midst of the liquid sample by a servo-controlled solenoid. The sample cell is suspended from a conventional balance and weighed with and without activation of the solenoid. Pure water is used to standardize the apparatus. Advantages of the method are listed, and specific design features discussed. The present equipment is used to measure densities from 0·7 to 2·9 g cm⁻³ at temperatures from 20 to 150°C and pressures up to 700 kN m⁻². An estimated accuracy to ±50 p.p.m. is attained with a sample of volume 6 cm³. The results of measurements on benzene and hexafluorobenzene are presented.

The design of a metal-foil current shunt for the absolute measurement of currents of the order of 100 kA and 100 ns duration is considered. When the metal foil is thick (> 100μm) the risetime of the shunt is determined by the time of diffusion of current through the foil in agreement with the calculated value, but as the foil thickness is reduced, pulse transit-time effects are observed to limit the risetime to the order of 5 ns. Optimization of the shunt configuration to give the best time response and to meet the requirements of high voltage output and high current operation in a specific applications is discussed.

By modifying Hopkin's frictionless cam suspension system and properly balancing the new cam and its suspension, an apparatus has been designed which enables the accurate maintenance of constant stress when forces as small as 0·1 N (0·022 lb) are involved. Means of controlling the force and measuring the extension during the initial or loading stage of the constant stress test are described. Using the apparatus in combination with a new method of measuring the derivatives of strain, the feasibility of obtaining accurate ( over umlaut, over dot) plots is demonstrated.

A description is given of a set of resonant cavities and other equipment for the measurement of dielectric properties of dilute solutions of polar compounds in nonpolar solvents in the frequency range 0·8-35 GHz. The accuracy of the method is estimated with the help of theoretical and experimental results. Some measurements are presented to show the applications of resonant cavity techniques to the measurement of dielectric properties.

A cell is described suitable for studying the physical adsorption of krypton labelled with krypton-85. The aim was the measurement of the beta rays from the adsorbate. Inside the cell a semiconductor detector is set on the metallic sample container. In order to achieve a good temperature equilibrium of the sample with the cryogenic bath, the walls of the cell, made of brass and immersed in liquid nitrogen, are thermically insulated from the upper part of the apparatus by a soldered glass joint. For each temperature, the detector polarization is adjusted to give the same pulse spectrum. Making expedient corrections enables one to obtain a proportionality between the disintegration rate and the surface area for a massive solid or the specific surface area for a dispersed solid. In the latter case, a counting rate of 850 impulses per second corresponds to a specific surface area of 1 m² g⁻¹ for a coverage of unity. Roughness factors measurement is a potential application of this study. This instrument is well adapted to the measurement of other radioactive adsorbates emitting alpha or beta rays with energies down to that of carbon-14.

A simple apparatus for loading a carrier gas with a vapour is described. Performance and some applications are given.

An experimental arrangement is described which was set up to measure the energy loss spectra of electrons which have passed through thin specimens in the electron microscope. It consists of a nondispersive filter lens which rejects electrons of less than a certain energy, determined by the voltage of the central electrode. By modulating this voltage with a small ac component and measuring the resulting modulation of the transmitted beam, the apparatus can be used as an energy analyser. In this paper, the process of `differentiation by modulation' is reviewed and the effects of using different waveforms and frequencies examined. Also discussed are high-voltage insulation and breakdown in vacuum, the effect of focusing the beam on the phosphor (which was used as the electron detector), and limitations upon possible sweep speeds. A novel feature of the system is a 2 kHz optical link used to supply a synchronizing signal to the high-voltage line.

The energy resolution of the system comes close to the theoretical minimum of about 1·5 eV. At low accelerating voltages output noise is almost entirely shot noise, but above 60 kV microdischarges increase the noise level substantially. Noise from these two sources limits the usefulness of the system for measuring low currents.

The operating principle of a swirl flowmeter is reviewed and it is shown that the output of the instrument should be linear and independent of viscosity and density. Test results concerning a commercial meter used with air and high pressure gas are given.

An apparatus is described for rapid specific heat measurements on irregularly shaped samples between 200 and 1000°C. It incorporates the desirable features of both the radiation and the drop calorimeter. The sample is heated in an induction furnace and then inserted into a copper tube. The temperature of both sample and copper tube is measured as a function of time. From these data it is possible to calculate the heat capacity of the sample.

An optical hot-stage microscope has been developed to study the growth kinetics of individual bainite needles in plain carbon and low alloy steels. A description of the apparatus is given, together with typical results obtained.

Two known methods of measuring the displacement of a light beam double dagger are discussed and it is shown that while neither is really satisfactory for accurate measurement, except under closely controlled conditions, a combination of the two methods gives greatly improved resolution and linearity, particularly with a light source having an arbitrary intensity distribution.

It is shown that a wide variety of transfer functions (electrical output against displacement) could be produced using this method and some possible applications are suggested.

A linear system using this method has been constructed providing a displacement range of 15 mm with an ultimate resolution of 5 μm.

A plasma arc light source is described, the characteristic properties of which are produced by an auxiliary electrode which generates a localized constriction and stabilization of the plasma column.

A description is given of the principle and applications of a new method of laser microanalysis. In this method a thin foil sample to be penetrated with the laser pulse is used. The advantages of the method, as compared with the current methods of laser microanalysis, are simpler construction of the apparatus, better optical efficiency and greater certainty in analysing small structural details, e.g. in alloys and petrographic samples.

A simple technique for the rapid display of dispersion characteristics applicable to any dispersive medium is described. Results are presented for the propagation of ionization waves in the frequency range 5-50 kHz on a helium gas discharge. Comparison with previous point by point determinations shows that not only is the measurement time drastically reduced, but also a reduction in random error is obtained.

Three methods are described for temperature stabilization and regulation for quenching and annealing experiments with a metal wire in a helium cryostat. All three methods use a potentiostat as a fast electronic control unit and current supply. Two methods are for temperature control for annealing an iron wire in high vacuum and for quenching the wire in liquid helium from temperatures higher than 950°C. The third method makes possible the quenching of iron wire, 1 cm above the liquid helium, from temperatures between 950 and 700°C.

An apparatus is described for the determination of the apparent densities of solids by a flotation technique. The method developed allows the density of about 0·001 g of sample to be measured to within ±0·002 g cm⁻³.

A simple instrument for making observations of the water vapour content of the earth's atmosphere from the ground is described. The instrument compares the intensity of solar radiation in and on the edge of water vapour absorption bands at 0·94 or 1·87 μm.

The rotor tube is designed for use with the rotating-wall dc arc plasma furnace. It is constructed to present a water-cooled and near-cylindrical boundary wall to the plasma chamber within which arc columns may be contained and expanded in the furnace. Two types of silica window are let into the rotor tube. These permit visual observation of objects and phenomena which occupy an extensive part of the plasma chamber, and enable spectroscopic observations to be made of material in planes perpendicular to the axis of the arc column at all points up to the inner wall of the rotor tube. They also interrupt electrically conducting paths in the rotor tube which could otherwise provide low-resistance paths by which expanded arc columns could be short circuited. This leads to greater stability of expanded arc columns.

A counting rate plateau ends when the gain of the system is such that spurious pulses are detected. For those radiation detectors in which the majority of spurious pulses are produced in a relatively short interval of time following a genuine pulse, a very sensitive method for detecting the end of the plateau consists of observing only those pulses which occur within a few tens of microseconds after a genuine pulse. The gain in sensitivity can be as much as several orders of magnitude over the conventional method and is greater for lower counting rates.

A novel method of tumbling a rock sample during demagnetization for palaeomagnetic work is described. The rock is enclosed in a perspex sphere and supported on an air jet within the demagnetization coils.

An instrument has been developed to drive modulation coils to produce Zeeman modulation in nuclear quadrupole resonance spectroscopy. A sequence of alternately negative and positive current pulses of up to 4 A, spaced by no-current intervals, is produced. The frequency may be as high as 500 Hz, since no electromechanical components are employed. The instrument is described in detail and sample resonance curves are presented.

A cell has been constructed with a thin film electron transparent window and a built-in transmitted electron detector for the examination of specimens in the scanning electron microscope at atmospheric pressure and in the presence of water. At 20 kV a resolution of approximately 0·1 μm has been attained with wet polystyrene latex spheres, human red blood cells and microorganisms of pond water.

A reliable method is described whereby electrical power can be supplied to antimony generators as used in the processing of image tube photocathodes.

A new technique for realization of magnetic contrast from thin ferromagnetic films in the transmission electron microscope is described. A phase shifting plate modifies the low angle diffraction pattern formed in the objective focal plane and leads to image contrast from areas of magnetic gradient.

A simply constructed, end-on type photomultiplier (EMI 6256S) cooling device is described, capable of maintaining a preset temperature by use of cooled dry gas. Through the use of this design, heated windows and difficulties of condensation are avoided.

An attachment for the Philips vertical x-ray diffractometer enables x-ray diffraction patterns to be recorded from a specimen under known stress. It has been designed for use in the plastic region of the stress-strain curve and the maximum applied load is 9 kN. The specimen alignment device is described and performance accuracies are given.

A pulse transmission mode, Q-switched Nd³⁺ oscillator is described, in which both Q-switching and cavity dumping are accomplished using a single Pockels cell, the resulting pulse being triggerable with approximately 100 ns jitter and having a width of 6 ns and a rise time of 1 ns.

When an electromechanical drive with feedback is used in Mössbauer measurements, the error signal between the reference and the velocity voltage contains a component at the working frequency and noise. A circuit is described which measures both components separately. The device facilitates precision calibration for sinusoidal motion and interrupts measurement if the disturbance level becomes too high.

A circuit is described which can be used to control the electrolytic thinning of metal tips for use in field-emission microscopes and similar devices. The process is automatic and can be applied to any electrolytic tip polishing method devised without modification of that method.

A simple circuit is described which allows the temperature of a water bath to be controlled to within ±0·005 degC over the range 5-60°C, the set point being easily adjustable.

A circuit is described for detecting insect movement by sensing capacity changes in a balanced system of conductors placed close to the insects. The instrument uses readily available operational amplifiers in place of wire wound inductors and transformers to give a stable output and repeatable results, with a sensitivity of more than 300 V pF⁻¹.

An apparatus is described for the continuous measurement of stresses in electrodeposits during plating. The bending moment generated by plating on one side of a thin strip is measured by a pair of piezoresistive transducers which are used to restrain the free end of the strip.

Using a detachable motor unit, the goniometer is controlled by commands input on punched paper tape. Basically the goniometer is directed, at a speed of 2° 2θ min⁻¹, to angular ranges of interest over which step scanning takes place. The count obtained after each step-scan is output on to punched paper tape and a printer. The equipment is straightforward, relatively cheap to manufacture and can be attached very easily.

A strain-gauge pressure transducer is described that has been constructed for blast measurements in water with a time resolution of 25 μs at 0-400 b. Special care was given to the damping of chock-induced signals by using an epoxy resin for the sensitive element which is suspended in two Teflon liners.

A modification of a normal electromechanical Mössbauer source driver is described, which enables it to be used in the `moving absorber' geometry.

A description is given of a device which uses the thermal expansion of a metal rod to bend at a constant strain rate alkali halide single crystals for use in piezoelectric and internal friction studies. Plastic strains of approximately 10⁻² have been produced in potassium chloride and lithium fluoride at strain rates of about 10⁻⁷ s⁻¹.

An extended version of the linear critical-angle refractometer for liquids is described; it shows directly, on a two-dimensional display, any variations of refractive index in one direction. It may be used to inspect the distribution of concentration or density in flow systems and in mixing and diffusion processes.