Table of contents

A method is described for the measurement of the relative phases of beams of laser light diffracted from a centrosymmetrical two-dimensional optical diffraction grating. The method relies upon the observation of interference effects when adjacent orders of diffraction yield overlapping beams of parallel light. The Fresnel diffraction pattern recorded is crossed by interference fringes whose positions and intensity distributions are governed by the phases and amplitudes of the diffracted beams.

Computer simulation of the diffraction pattern indicates the possibility of phase recovery from patterns given by centrosymmetric diffraction gratings when two, three or four beams overlap, and suggests that the method may be extended to diffraction patterns from non-centrosymmetric gratings also. The potential of the method as an analogue for phase determination in crystallographic problems is indicated.

This paper describes a miniature lens and image conduit assembly which permits the observation of radial luminosity distributions in cylindrically symmetric plasmas, when the configuration of current-carrying conductors makes the plasma inaccessible to conventional high speed photography techniques. Density profiles obtained with the assembly are indistinguishable from those measured by the usual method.

Optimum sampling and smoothing conditions for digital recording of spectral lines are derived for a system consisting of a spectrometer with CR-filter output, a sampling instrument for measurement of the spectrometer output and a processor applying a quadratic smoothing polynomial on to the sampled signal. Relevant experimental parameters for smoothing of the noise process, for the integral square error and for the signal-to-noise ratio will be discussed, and a set of practical rules to obtain efficient signal enhancement is given.

The design of a neutron spectrometer capable of performing a number of experiments is described. Rocking curve measurements using two different crystal-to-detector resolutions are shown as well as a typical count-rate spectrum.

A method is described by which the x-ray absorption coefficients of nonuniform thin samples can be accurately determined. In addition the method yields the specimen thickness.

A density balance which uses an electromagnetic method of weighing has been constructed to measure densities in the range 0-4 g l⁻¹, in order to measure gas imperfections. The accuracy of measurement is to better than 0·005% with a limiting accuracy to about 2×10⁻⁵ g l⁻¹ at low densities. The balance should find many applications in other fields.

The integrating nephelometer is a convenient instrument for measuring the atmospheric scattering coefficient at a point and may be used to estimate visual range. This paper describes an instrument of this type, developed for use in a study of the relationship between visibility and the concentration of air pollutants. The instrument has a stabilized response and is suitable for automatic operation over long periods. Difficulties of calibration are discussed and the results of a field trial are presented.

A device has been developed for measuring the surface temperature of particles of 250 μm diameter at temperatures in excess of 300°C. The basic component of the instrument is a liquid-nitrogen cooled indium antimonide cell used in conjunction with a mechanical chopper and signal amplifier. A system of two-colour pyrometry is employed in which two narrow bandpass filters, centred on the 3·1 and 4·5 μm wavelengths are alternately interposed in the beam of radiation from the source at a frequency of 100 Hz. The device has been developed especially for determining the surface temperature of captive fuel particles, but has been used in other applications, notably the temperature measurement of heat exchanger surfaces, where its high sensitivity and non-contact mode of operation have proved particularly advantageous.

A swept frequency rf mass spectrometer of small path length has been developed. This works on the principle that each ion species present in a sample can be made to produce a characteristic waveform which can be identified in the output. A scan of a mass range can be performed by analysing the output waveform resulting from one rf sweep. While, in general, a complete spectral analysis would best be performed by computer, the required information for specific applications might be obtained more simply. The overall ion path length of the prototype instrument was 0·705 cm and its aperture diameter 1·6 cm. The large aperture gives the instrument high sensitivity which is still further increased by the fact that most of the wanted ions entering the head contribute to the output waveform. The measured sensitivity of the prototype instrument was 20 μA torr⁻¹ for argon, but this was in the absence of any attempt to optimize the ion source characteristics. The resolution can be high, the exact value depending on the sampling process. The physical characteristics of the prototype limited the mass resolution to about 150 but a resolution of 200 should be easily attainable, and a mass range of 1-200 could be swept in a time of the order of 10 ms. Smaller path length instruments could be used for measurements at pressures up to about 0·1 torr. This, together with the compactness of the instrument, offers opportunities for its use in the investigation of the ionosphere and of planetary atmospheres.

An improved tech nique has been developed for elevated temperature compressive creep testing at constant stress. The maintenance of stress is through a servo control involving load and strain signals, and is based on the assumptions of constant volume and uniform deformation in the material. Strain is measured directly off the gauge length of a waisted specimen to avoid `bedding-in' effects occurring at the interfaces between the specimen and push rods. Axial stability is achieved by tapered ends to specimen that are located in rigidly aligned push-rods.

Successful application of single vessel continuous crystallization in the sugar industry depends on the ability to separate the large from the small crystals while still suspended in the mother liquor. Screens whose apertures are equal to the separation size of the crystals are not satisfactory because they rapidly blind with growing crystals. A technique is described which on the laboratory scale successfully separated crystals into two size ranges using an overflow centrifuge. The clearances between the working surfaces are great enough to ensure that no blinding occurs.

Fused silica surfaces polished for long periods while only water is added to the lap after a final application of cerirouge are shown to have a rms roughness of about 0·25 nm. Such small irregularities are resolved by fringes of equal chromatic order only when the apparatus is used under best conditions. In the case of silver reflecting films, highest lateral resolution and highest resolution in depth are obtained for a first order fringe in the red region of the spectrum.

A new scanning Fabry-Perot interferometer is described. The scanning time can be varied from 20 ms to many minutes. The instrument was tested on a low-temperature, low-pressure hot-cathode discharge in helium.

Curves are given of the optimum tilt angle for stereo photographs as a function of foil thickness and magnification, to give a good stereo impression in a stereoviewer.

Some problems with the vibrating sample technique for obtaining magnetization curves of superconducting samples are discussed. The construction and performance of a simple integrating magnetometer which overcomes some of these difficulties is described.

A simple and highly portable device is described for bonding thermocouple and other fine wires in an inert atmosphere by a resistance welding process.

The paper describes a focusing coil for use, instead of a solenoid, for focusing electrons in a field-ion image converter. It offers advantages of smaller size, weight and cost, and it makes possible line-of-sight access to the specimen. Graphs of magnification, rotation and excitation plotted against lens position are presented, together with micrographs illustrating the performance of the lens, and it is concluded that the lens is in no way inferior to a solenoid.

With increasing sensitivity of the electron spin resonance spectrometer, stability of its bridge circuit becomes important. An automatic balancing system of the bridge circuit and its successful application to a parametron spectrometer for improving the long-term stability are described. It is shown also that the same system can be employed as a marker signal generator for easy adjustment of the spectrometer.

A simple and safe `two-zone capsule' method for the preparation of high purity, metal-sulphur alloys is described.

A well-known microwave method to measure electron densities is based on the effect that the resonance frequency of the cavity shifts due to the presence of plasma. Here, a method is described which can be applied to obtain a direct display of the frequency shift as a function of time in the case of varying plasma densities.

A new device for the mechanical transmission of rotary motion to ultra-high vacuum is simple and sufficiently compact that two independent devices can be mounted in the same standard 1½ in port.

A simple technique using a scanning electron microscope in transmission mode has been developed for measuring the profiles of razor blades back to 1-2 μm from the cutting edge. The results obtained are consistent with data obtained by replication and interferometry.

The rotating voltmeter is an instrument used for high voltage measurement. The instrument presented here is designed for the measurement of high dc voltage up to 100 kV. The chief advantage of this instrument is that it draws practically no energy from the source at all.

The torque adjusting mechanism of a Zimm-Crothers type viscometer was made more convenient, reproducible and precise by use of a fixed stator, an adjustable magnetic drive yoke and spacer blocks. A photoelectric device was added for timing the rotor speed and counting the revolutions. A photoconductive cell, associated optics, relays, an electric timer and an electrically triggered counter contribute a degree of automation to the viscometer.

In order to improve the quality of the electron channelling patterns obtained with the scanning electron microscope, the high voltage applied to the photomultiplier is brought under the control of the video-level, from which it is then possible to extract a properly integrated fraction. These two modifications are sometimes useful in routine scanning electron microscope work.

A cryostat is described which allows continuous control between 3·6 and 300 K. Temperature control is achieved by controlling the amount of liquid coolant flowing into a heat exchanger which is located very close to the sample. The temperature is regulated by feedback control of the power to an electrical heater wound around the heat exchanger. Temperatures in the liquid helium range can be controlled for a time to up to more than 1 h with an accuracy to ±0·005 K around 10 K and ±0·02 K around 30 K.

By applying a varying magnetic field perpendicular to both the applied static field and the varying rf field, the overlap of central (M=½->M=−½) esr spectral lines by outer fine structure may be reduced and even eliminated. Overlapping spectra from ions in nonequivalent crystal-field sites may also be resolved, using this technique.

A simple method is presented by which magnetic and structural diffraction effects may be differentiated when thin ferromagnetic films are viewed under high resolution Lorentz defocused microscopy. The technique utilizes the sense of the electron velocity on the direction of the Lorentz force in the film.

The apparatus described provides a simple method of saturating a carried gas stream with the vapour of a volatile anaesthetic agent at a known temperature. With the carrier gas stream between 100 and 700 ml min⁻¹, dew point determinations indicated a saturation better than 99·5% at the temperature of the water bath and refractometry was consistent with full saturation.

A prototype annular curved plate electrostatic analyser with a large geometrical factor and ±5° angular, and ±5% energy, resolutions has been constructed to measure particles in the range 1-10 keV. A description of the instrument and its performance under laboratory conditions is given.

This note describes a simple, inexpensive, but very effective device for doing cathodoluminescence studies on the JSM I scanning electron microscope.

The surface charge densities on insulators are measured using a capacitative probe. The theory of this device is given for the case of surface charge and for the more general case of surface and bulk charge distributions.

Improvements to a previous liquid helium stage are described. They include: (i) the possibility of changing specimens through a small airlock without breaking the microscope vacuum; (ii) the possibility of changing coolant very rapidly by use of a transfer line which is made independent of the specimen cooling circuit; (iii) reduction of vibration caused by coolant flow.

Two simple synchronous gates employing MOSTS are described. The hold time, defined as the time required for a stored voltage to decay by 1%, is six hours in one case and 20 minutes in the other. The corresponding shortest gate times which have been achieved are 100 ns and 10 ns respectively.

A miniature mass spectrometer on a rotary pump vacuum system has shown that hydrocarbon contamination can be reduced from greater than 1 mtorr to less than 0·1 μtorr by using an alumina foreline trap.