Table of contents

A heat flow probe, with which both temperature gradient and in situ thermal conductivity in sediments can be measured, is described. The relevant theory and design requirements are presented. Results of thermal conductivity measurements on sediments in Wellington Harbour are given and compared with values from a needle probe and from a standard divided bar apparatus. It is concluded that the accuracy of the in situ thermal conductivity measurement is comparable to that from the divided bar and that the instrument permits heat flow measurements to be made more reliably and conveniently than by any other method.

A critical survey of the published data of the focal properties of magnetic electron lenses has revealed several inconsistencies between the findings of various authors. Some of these can be ascribed to errors in computation, but others stem from inherent limitations imposed by the conventional presentation of results in the form of `universal' curves or from the use of relative rather than fixed units, such as centimetres. The results of more accurate computations, especially of spherical aberration, are presented in a new form which is particularly suited to the determination of lenses of optimum performance. The results are applied to the question of determining the best possible objective lens for high resolution electron microscopy.

A simple continuous transfer liquid helium cryostat for an ultra-high vacuum field ion microscope has been constructed. In this cryostat the liquid helium is continuously transferred from a conventional 30 or 50 1 storage vessel, employing a standard transfer line, to a small reservoir which is in direct contact with the field ion microscope specimen holder. The enthalpy of the outgoing cold helium gas is used to cool a copper radiation shield which surrounds both the specimen holder and the reservoir section of the cryostat. The economical operating temperature range of this cryostat is 8°K to room temperature with a temperature stability of better than ±0·1 degK over most of this temperature range. Details of construction and the operational characteristics are presented.

A new type of critical-angle refractometer for liquids is described; it has a linear scale of refractive index and freedom from aberrations, the accuracy attainable being limited only by surface quality and diffraction effects. Prototypes even without optically worked surfaces can be read to about ±0·0002 in refractive index - within an order of magnitude of their diffraction limit. Several forms of the instrument have been made; this paper describes a single-entry direct-reading probe, and also an in-line annular version mounted flush with the wall of a pipeline. Visual reading has been used so far, but methods of achieving an electrical output are proposed.

A digital scanning-densitometer system has been assembled in this laboratory for the purpose of processing x-ray diffraction films. The system consists of a scanning densitometer of the rotating-drum type, linked to a small computer equipped with a magnetic disk memory. In 5 min, it is able to scan a 5 in × 5 in film on a raster 200 μm×200 μm and store the entire digitized image (about 400 000 optical density measurements) on a disk. The optical density measurements range from 0·0 to 2·2 with 256 grey levels. Because of the rapid-access capabilities of the disk memory, the film image can be processed efficiently and automatically by a computer program to evaluate the intensity of the desired reflections. This instrument is capable of making an integrated intensity measurement in about 0·6 s with an accuracy to about 3%.

Using an idealized model it is shown that, to minimize errors in double-spiked isotopic analyses, spike mass numbers should alternate with normal. The comprehensive error analysis which follows assumes that the individual ion currents are the independent varietes for statistical purposes: errors in these are obtained by combining (i) a coefficient of variation e_P due to fluctuations in ion emission with (ii) a resistor noise index e_R and (iii) a shot noise index e_S: the noise indices are the ratios [error due to noise]/[error (i) due to emission fluctuation] for the largest ion beam in the spectrum. Methods of computing error multipliers (operating on e_P) from e_R, e_S and the isotopic abundances, are developed. For a particular element each error multiplier can be regarded as a function of two variables, the ratio of the two spikes selected and the spike/normal ratio, which can then be optimized by numerical methods.

Optimum values of spike composition and spike/normal ratio are given for observations of isotopic fractionation of lead, molybdenum and iron using various pairs of spike mass numbers. If both noise indices are taken to be zero the minimum error multipliers are not very much increased by deviations from the ideal model. When e_R is given values corresponding to experience with a typical electrometer, it is shown that satisfactory results would be obtained on Pb and Mo with quite low ion currents, but that for iron, because of its difficult isotopic composition, the maximum ion current should be as large as possible.

Some possible deviations from first-order fractionation theory are considered. A general algebraic analysis for the determination of radiogenic isotopes is given, and different approaches to fractionation computations are discussed.

A four-electrode a.c. potentiometer employing bright platinum electrodes has been developed for measurement of the conductance of electrolyte solutions and molten salts. Errors due to polarization and the state of the electrode surfaces are eliminated.

A voltage generator capable of delivering pulses of up to 30 kv with subnanosecond risetimes and duration adjustable in the range 4-40 ns has been developed. The design is based on a hybrid transmission line system and employs as the switching elements spark gaps through which an overvoltage is passed, at atmospheric pressure. Unwanted voltage wave reflections have been adequately suppressed and oscillograms of typical pulses are included.

A `girdle' type high pressure unit for the pressure range 20-70 kb is described and its design and loading characteristics are discussed. The pressure intensification effect has been investigated and the results enable an estimate of its magnitude to be made.

A thermoluminescent dosemeter reader is described which incorporates autoranging facilities, automatic tray vibration and fixed period nitrogen-flushing. The print-out is automatic and thus the reader is suitable for use by semi-skilled personnel.

An electron bombardment furnace has been successfully used in conjunction with a specially designed extensometer to measure thermal expansion coefficients up to 2300°C. In order to calibrate the apparatus, thermal expansion coefficients of tungsten from 1700 to 2300°C have been measured. The results are in good agreement with the data of Worthing and V'Yugov and Gumenyuk.

The construction of a laboratory arc melter is briefly described. The charge is melted in a water-cooled copper mould utilizing a nonconsumable tungsten electrode. The maximum power consumption of 24 kW is supplied by a commercial rectified d.c. welding unit. Melting procedures and some applications of the melter are discussed.

A method of measuring small degrees of polarization of luminescence emission and excitation in the presence of wavelength-dependent instrument polarization is outlined. The method requires the measurement of radiation intensities with the crystal positioned parallel and perpendicular to a reference direction in a plane perpendicular to the optical axis of the system. The accuracy of the method is considered quantitatively and computed curves are presented to show the range of validity.

A 12 m measuring base is described which is fabricated from steel tube using internal water circulation with an on-off control system to regulate temperature to 0·02 degC. Dimensional changes over several hours have been shown to be controlled to within 0·2 p.p.m. from continuous records made with a tensioned-wire deformation transducer capable of 0·01 μm resolution.

The radiometer was built to obtain information about the temporal and geographic variations of night sky radiation between 1 and 2 μm. The equipment is portable and can be run from secondary batteries by use of an inverter. Provision is made for paper chart and/or digital magnetic tape recordings of the data which are later reduced by computer. Some novel features are included, notably an ellipsoidal light-pipe to give wide angle coverage whilst still providing collimation for the interference filters which isolate the wavelengths of interest. Also a magnetic phase reference pick-up is used to drive the synchronous rectifier.

An infra-red cell is described which involves a gas diffusion and heat gate principle to obviate use of a Dewar system at low temperatures. The cell can also be used up to 120°C.

A slide is described which achieves precise linear motion by means of glass flat surfaces. Parallel motion to within 2/5 second of arc has been recorded over a 2 cm travel.

A simple and reliable vacuum seal for electrical leads is described. The seal is made by passing the leads through a Neoprene disk.

The construction is described of a simple device by which the fluorescence of very thin liquid layers can be measured. The effect of finite absorbance on the fluorescence yield of the layer is calculated, and compared with experimental values obtained by varying the thickness of a layer containing both fluorescent and absorbing components.

A vapour deposition method for the production of thick cadmium sulphide transducers with resonant frequencies as low as 20 MHz is described. The transducer films are insulating and polycrystalline with the crystallites' c axes oriented normal to the substrate. They were grown at about 1 μm min⁻¹ by co-deposition of cadmium and sulphur inside an inverted dish.

An automatic surface balance which can be used at the oil-water or air-water interface is described. The balance has a pneumatic sensing and amplifying device which records the surface pressure. The balance is simple and inexpensive to construct and is automatic in operation.

Herein is described a method by which component gases can be weighed as they are added one by one to a gas mixture. The float balance, designed for the purpose, is capable of determining a maximum mass of about 3 kg of a gas mixture contained in a cylinder of mass about 5 kg with a sensitivity of ±0·1 g mm⁻¹ of the stem height.

A simple, low dissipation liquid helium depth gauge using carbon resistors as sensors is described. A method for deciding definitely whether a resistor is in or out of liquid is noted.

A technique is described for the rapid assembly of carbon dioxide laser tubes using standard glass pipeline units. This method has been successfully used to construct a carbon dioxide laser amplifier operating at 10·6 μm and has proved both simple and convenient.

Two types of resistance-heated furnaces for molten salt spectrophotometry are described. Both have low thermal gradients in the cell space. One furnace fits the sample compartment of a Cary model 14 spectrophotometer and operates up to 400°C. The other is used with a Cary model 14H high-temperature spectrophotometer at temperatures up to 1000°C. The molten salt samples are held in square silica cuvettes with a 1 cm optical path.

A small rocket-borne amplitude-modulated radio receiver, developed for use in Faraday rotation experiments which measure the electron density of the lower ionosphere, is described. The receiver performs well over a range of frequencies of 1-4 MHz, has an effective bandwidth of 2·2 kHz and a sensitivity of 5 μV m⁻¹.

This note describes a portable device designed to transfer specimens from a high vacuum evaporator to an AEI EM6G electron microscope in a vacuum better than 0·1 mtorr at liquid nitrogen temperature. Methods are described for the reduction of the contamination of the specimen by ice in the electron microscope.

Precise optical alignment of a direct reading spectrometer can be achieved by a lateral movement of the entrance slit. This movement towards the optimum position is controlled automatically with the aid of a digital counter and a stepping motor.

Makrofol K G, the polycarbonate of 4.4 prime-dihydroxydiphenyl-2.2 prime-propane, which can be obtained as 2 μm thick film, is suitable for flow proportional counter windows. When correctly fitted it is durable and, of commercially available films, has the largest transmission for the K-radiation of the light elements, Z=11-16.