Table of contents

Ion beam systems and their component parts used for analysis of solid surfaces are reviewed. The energy range under consideration for the primary beam system is of the order of a few keV to several hundred keV with ion currents up to 1 mA. Ion production, acceleration and focusing, analysis, beam handling and detection facilities are discussed together with some examples of complete systems.

A modification of a scanning Lang camera is described which enables scanned Berg-Barrett reflection topographs to be produced with a resolution superior to that obtained with the unmodified camera.

A method is described for acquisition and on-line correction of fluorescence data using a laboratory instrument computer.

Measurements of electron beam currents for determination of photographic exposure times and for determination of the radiation dose to which the sample was subjected were facilitated by a logarithmic picoammeter which indicated currents as low as would produce a useful image in a few seconds on a fast emulsion. Since the meter was logarithmic it also indicated the much higher currents ordinarily used without a scale change. Calibration of the electron collection efficiency of the focusing screen used to collect the current enabled the actual current density at the sample to be determined.

General circuits for the display of the peak value achieved by a transient signal are described. Poor design can result in errors of up to 15% occurring, whereas accuracies of 0.1% are possible. The design criteria are discussed in the context of one particular circuit for measuring or displaying the peak voltage on a capacitor used to integrate the photoelectric charge from a pulsed laser detector. The circuit described can acquire a peak in about 100 mu s; faster operation is possible with faster analogue amplifiers or reduced voltage swings or reduced display times. The type of circuit discussed may also have applications for processing the signals from nuclear particle detectors.

The design criteria of current-carrying springs for high temperature ribbon filaments are more demanding than for cylindrical wire filaments. A spring, which was found to be satisfactory for a tungsten ribbon up to 2500 K, is described.

The complex permittivity of films may generally be derived from microwave resonator measurements. Especially for anisotropy measurements, the suitability of different resonator types depends on the degeneracy of their resonance mode. If it is degenerated, degeneracy is lifted by anisotropic materials, the frequency splitting and intensity of resonance depending on anisotropy and direction of principal axis, respectively. Frequency splitting is observed only with high resolution, as obtained by open resonators. Experiments with an open resonator (Q>10⁵) and results on polyethyleneterephthalate (permittivities parallel to surface) at 19 GHz are reported. They are in agreement with results at 9 GHz.

The plastic scintillator tip used as the secondary electron detector of a scanning microscope has a limited working life particularly with high electron beam currents. A detector with an extended life and capable of working up to beam currents of 3*10^-6 A has been made by replacing the plastic scintillator tip with one made of a lithium glass scintillator.

A new method for making reproducible and mechanically stable superconducting weak links is described. The method is based on the fact that the critical current of a weak link, in the form of a superconducting filament inside a semiconductor, or a superconducting film on a semiconducting substrate, can be controlled by diffusion into the semiconductor.

A pair of sliding mirrors in the optical path of a single-beam reflectometer allows relative measurements of reflectance at nearly normal incidence to be performed with sample and reference mirror kept stationary. The system is suited for small samples.

Six liquid flow generators of different types are described. They have been developed principally for use with liquid flow calorimeters which require a continuous supply of liquid over the space of an hour at an optimum flow rate of 1.5 cm³ min^-1 which is constant to at least 1%. Three simple pressure-driven generators which meet with this requirement are described. A precision hydrostatic flow generator which will supply 900 cm³ of liquid at a rate which is constant to better than 0.1% is also described. Details of the design of a precision screw- driven piston and cylinder pump are given. This pump will supply two liquids simultaneously, each at a flow rate which is constant to better than 0.1%. Alternative piston and cylinder assemblies which allow very small quantities of liquid to be pumped at very slow flow rates are also described.

A partly new and sensitive technique is described for measuring the net charge on a small object. The electrostatic energy of a charged circular insulator plate is calculated. The technique is then used for energy measurements on discharges from insulator surfaces. Simultaneously with these measurements the discharges are photographed. A powder technique is also used for studying the surface discharges.

The electrostatic potential of a quadrupole with plane electrodes and its use as an energy filter are discussed. Because of the inseparability of the equation of motion, the energy spread and focusing conditions must be derived by means of trajectory computation. The transfer of the results to instruments with cylindrical symmetry is outlined.

The spectrometer uses an unbalanced AC bridge and records the real or imaginary component of permittivity on a chart recorder over the frequency range from about 1 Hz to 1 MHz. The measured sensitivity extends to values of loss tangent of about 10^-3 although the ultimate sensitivity is expected to be higher. The spectrometer is intended primarily for use with solid samples with permittivities described by the Debye equations.

Methods are discussed of correction for photon pile-up effects which occur when measurements of intensity time dependence of time-varying light sources are made by single photon counting. A composite inhibit function improves the resolution of a conventional inhibit circuit to allow substantial rejection of pile-ups. In all practical cases this technique is at least as accurate as applying a theoretical correction. The particular advantage of the inhibit function lies in its ability to handle sources whose intensity fluctuates from one experimental cycle to the next. As an example an ADD-SUBTRACT technique which can be used to improve the data in experiments to measure radiative lifetimes is discussed.

A two-beam infrared optical system is described which uses a single reflecting chopper to separate and recombine the sample and reference beams. This enables the same part of the source and the detector element to be used for both beams. This two-beam system has been incorporated into an apparatus to measure the magnetoreflectivity of polished semimetallic samples held in an 8.0 T superconducting solenoid. With this apparatus changes in sample reflectivity of less than 0.1% can be readily detected for a wavelength resolution of 1% in the range 1-14 mu m, and this has allowed several new features of the sample magnetoreflectivity to be found.

A simple robust device is described which was developed to sense the static head of the ambient air stream. It consists basically of two parallel circular plates each with a pressure tapping at the centre. The results of wind tunnel tests to establish the accuracy at different values of plate spacing, wind velocity, yaw angle and pitch angle are discussed. Accuracies better than 1% of the velocity head are readily achieved.

The use of various types of reflector with two simulated rectangular scintillation detectors (40.5 cm*15.2 cm*6.3 cm and 60.0 cm*40.5 cm*6.3 cm) has been investigated with respect to the efficiency and uniformity of light collection, by means of optical model experiments. It is shown that good efficiency and uniformity of light collection can be achieved by collecting light from one end of the detector only, through a single light guide, provided that the basic method of light reflection employed is total internal reflection. Various specular or diffuse reflectors placed close to, but not in optical contact with, the surfaces of the detectors increased the collection of light without seriously affecting the uniformity.

Australian water samples have been shown to have a much lower tritium content than samples in the Northern hemisphere, and quantitative assay of their tritium content is correspondingly more difficult. A gas proportional counter using butane prepared from electrolytically enriched water samples is described. The counter, which has better counting characteristics for low level tritium assay than most others described in the literature, has been applied to assay of both surface and underground water samples.

The effect of the detector time response function on the photocurrent autocorrelation function obtained by an analogue time correlation light-beating spectrometer has been theoretically and experimentally investigated. For the spectrum of light scattered from a dilute solution of spherical macromolecules, the photocurrent autocorrelation function is calculated to consist of two exponentials, this has been experimentally verified. With variation of the time constant of the photomultiplier anode circuit, it is possible to estimate the intensity of the scattered light.

Apparatus for investigating by light microscopy the effects on biological systems of hydrostatic pressures in the range 1-1600 atm at temperatures between 0 and 40 degrees C is described. The system has good resolving power as demonstrated by observation and photography of flagella 0.2 mu m in diameter. Possible improvements to the system are discussed.

A description is given of an apparatus which utilizes the mechanism of preferential adsorption on alumina (Al₂O₃) at a temperature of 20 K to achieve the separation of the ortho species from the para species of molecular hydrogen. Enrichment of the ortho component occurs within a cylindrical adsorber column approximately 50 in long and 1 in in diameter. The column is cooled by heat exchange with circulating helium gas from a two-stage electrically driven cryogenerator, thereby eliminating the need for liquid hydrogen and nitrogen coolants. Large scale production of orthohydrogen is possible since the system is capable of continuous operation for indefinite periods, and supplies orthohydrogen gas of 99% purity at a rate of 3-4 litres (STP) per hour. The design and operation of the separator are discussed in some detail.

An apparatus is described in which resistance thermometers may be compared in the range 4-90 K with high precision. It is used in routine calibrations with platinum thermometer standards in the range of the IPTS-68 and germanium thermometer standards at temperatures below 13.81 K, the present lower limit of the IPTS. The techniques used for making the measurements and processing the data are discussed.

Describes an apparatus for the study of ions produced by electron stimulated desorption at gas-covered surfaces. The target in the form of a single crystal is located at the centre of a retarding field energy analyser of hemispherical form. The identity of desorbed ions is determined by allowing a part of the ion flux at the collector of the energy analyser to enter a quadrupole mass spectrometer. A further mass spectrometer incorporated in the ultrahigh vacuum system housing the apparatus serves to monitor the gas composition. Preliminary tests of the system are described and the results of measurements of the interaction of oxygen and of carbon monoxide with the tungsten crystal (110) are presented to illustrate the performance of the instrument.

A simple and convenient way of measuring X-ray peaks recorded by a Si(Li) detector is to sum the contents of an appropriate group of channels in the pulse height spectrum. However, such measurements are susceptible to errors due to shift and broadening of the pulse height distribution with increasing count rate. The results of calculations and measurements of these effects are given. It is concluded that errors can be kept below 1% provided certain conditions are observed.

The design of detection coil systems for use in vibrating sample magnetometers is discussed with particular reference to those magnetometers which are mounted on conventional iron cored magnets. Experimental results are presented for two distinct types of coil arrangements which can be fitted into a 2 in (5.1 cm) air gap. It is found that one of these coil arrangements possesses an extremely broad saddle point. For example, the equilibrium position of the vibrating sample can be displaced by +or-2.6 mm, +or-6.4 mm or 4.8 mm in the x, y or z directions without causing a change of more than 1% in the output voltage from the detection coils.

The design of an improved uniform field magnetic electron spectrometer is described. The special choice of ray paths in the second principal section leads to the vanishing of the second order angular aberration term cuased by the fringing field. In analysis of the pencil beams, the resolution of the proposed prism is the best one in comparison with several other dispersive spectrometers. The resolution improvement by shifting the selecting aperture to the plane of minimum trace width is discussed. Finally, the shape of a nonsymmetric magnet, giving a maximum possible resolution for this type of spectrometer, is computed.

A monochromator is described that produces a very narrow band of X-ray wavelengths-only about one-fifth of the width of the spectral K alpha ₁ line. It makes use of high-angle reflections ( theta >70 degrees ) from a quartz crystal. With it, extremely accurate measurement of line profiles is possible. An assessment of its performance is given.

In the process of manufacture of doubly aspheric Schwarzschild-aplanat reflecting microscopes, the calculation (Burch 1947, see Abstr. A855 of 1947) of the offence against the sine condition of the simpler singly aspheric semi-aplanat design, was invalidated by an algebraic mistake. This letter corrects the algebra and gives computer-tabulated plots of the offence against the sine contition (OSC) for some semi-aplanats of infinite tube length.

It has been found that, when working in areas away from the glass laboratory, a bench torch is needed when only a hand torch is available. The simple device described is more than adequate, since, in principle, the user simply presses the torch into a V-block using only one hand if necessary. Also, being spring loaded, it is not restricted to one size of torch but has a range ¹/₄ in to ⁷/₁₆ in diameter.