Table of contents

The author principally describes molecular, gas-phase photoelectron spectroscopy using ultraviolet light excitation. An outline is given of the formation of a photoelectron spectrum. The elements of a spectrometer are fully described, including light sources, target configurations, electron energy analysers, and electron detectors. Spectrometer systems are reviewed with an emphasis on means of improving factors such as resolution and signal-to-noise ratios.

Improvements and extensions have been made to the techniques of sealing oriented magnesium fluoride crystals to metals, with a suitable glass solder. The technique for sealing a 38 mm diameter window in a 90 mm diameter stainless steel flange, 12 mm thick is described. The sealing of windows to all-glass devices is relatively simple using standard graded seals to soda glass and then with the solder glass to the window. The method of cleaning the mounted windows is also described.

A small triple-reflection-type polariser has been designed, whereby one component can be swung away enabling unpolarised light to be obtained without breaking vacuum. The polariser has the additional advantage that it can easily be attached to the frequently used DC glow discharge lamp. The test of the polariser by angle-resolved UV photoelectron spectroscopy on CO adsorbed on Ni (001) is discussed. The transmission of the polariser is found to be 10% with an estimated degree of polarisation of more than 80%.

A reliable system is described which is well suited for high-resolution, laser spectroscopy and for applications in laser photochemistry. High infrared power output (85 mW), long lifetimes of the laser crystals in operation (4 weeks), simple adjustment and remarkable amplitude and frequency stability have been obtained.

The method consists of determining the power P₁ absorbed by a surface from a beam of visible or near-infrared radiation, and of subsequently determining the power P₂ absorbed by a black surface from the same radiation. The wavelength lambda of the radiation is determined by one of a set of bandpass filters. The temperatures are measured by means of thermistors. The optical system consists mainly of a 250 W lamp, a two-mirror collimator, a bandpass filter and a condenser lens. Results are given for three surfaces that may be considered as selective surfaces for flat-plate solar collectors, a copper oxide surface, a black nickel surface and a black enamel surface covered with tin oxide.

A converter is described that is linear without adjustment or the use of precision components to a few parts per million. The main ripple components are shown to be at high frequencies, thus making the output filtering easier than for circuits using the simple mark-space ratio technique.

A description is presented of a Wien bridge oscillator for resistance measurement which generates 1 mV RMS across the unknown resistor, making the power dissipation sufficiently low for use in low-temperature thermometry down to about 25 mK.

A low-cost interface using an analogue-to-digital converter and conventional logic circuitry is described.

A simple, precise, non-trial-and-error method is described. The method employs a Unicam rotation camera as its primary tool and only requires one non-standard part. In addition to the usual equipment. The method can also be used for transferring crystals from one goniometer head to another.

An efficient monochromator is made by imaging a single graded filter on to itself so that the variation from red to blue is reversed in the image. This system transmits a large flux of continuously variable wavelength and narrow bandpass. It is compact and can be adapted for use with a circular filter.

In this instrument described, radiation is absorbed on plastic sheets glued to a brass foil. Temperature measurement is accomplished using thermocouples. No damage has been observed at peak densities of 130 GW m^-2 and energy densities up to 60 kJ m^-2.

An investigation is conducted to discern the effects of centrifugal and Coriolis forces on a rotating hot-wire. The probe is calibrated in a wind tunnel as well as in a rotating mode. The effect of rotation is found to be negligibly small. A small change in cold resistance (1.5%) is observed in the rotating wire. The rotation seems to have a negligible effect on the fluid mechanics, heat transfer and material characteristics of the wire. This is a significant conclusion in view of the potential application of the hot-wire probe in a rotating passage (such as turbomachinery).

A method of measurement using optical pyrometry is described. Equipment modifications are explained, and errors in estimating graphite specimen temperatures discussed.

An instrument is described for measuring the mass flow rate of dry conducting or non-conducting granular solids or powder. The capacitance-measuring electrode used offers no obstruction to the flow of the material and there are no moving parts to wear out. The principle employed is that of capacitance noise, by which the very small changes in capacitance which occur when particles move in a pipe or chute are detected. Applications to gravity-drop and pneumatic conveying and to measuring the output of short-blasting hoses are described. Materials measured include PVC chips, steel grit, aluminium oxide, glass beads and crushed walnut shell.

A precision dielectric cell and an experimental technique are described which may be used in conjunction with a fixed-ratio-arm AC bridge to measure conducting through to insulating fluids, including disperse systems. It is possible to cover a range 10-10⁵ Hz in frequency, about 1-10¹⁰ Omega m in specific resistivity, and any capacitance met in practice with excellent discrimination between the resistive and reactive components. A three-terminal fully shielded configuration is achieved without sacrificing mechanical accuracy and stability. Thin films of liquids down to a few micrometres thick can be measured, with concomitant provision for assessing electrode polarisation effects as an integral part of the measurements.

A system is described for measuring instantaneous concentration values in turbulent flow, when the levels of concentration are too low for conventional laboratory techniques to be used. The system is designed for use in the wind tunnel modelling of atmospheric dispersion. It consists of a small sampling valve, placed in the wind tunnel at the required measuring position, which injects samples of tunnel air into a carrier line of gas flowing to a flame ionisation detector. The low dispersive properties of laminar pipe flow are utilised in passing the sample to the flame ionisation detector. Tests show the system to be capable of measuring down to 1 ppm by volume of trace gas (propane) in air, with a 2 mm diameter sample volume and a 10 m carrier line, at a sampling rate of 2 s^-1.

A new feedback interferometer is developed with which not only the magnitude but also the sign of a phase change caused by a variation in the optical path can be measured. This is an important feature, for example, in plasma diagnostics. Phase quadrature is obtained by using two axial modes of a He-Ne laser. The two interference signals can be separately detected by virtue of the orthogonal polarisation of the two axial modes of the laser without Brewster windows. The result is a versatile, stable and accurate instrument. In the experimental test the sensitivity proved to be approximately ¹/₅ fringe at a laser wavelength of 632.8 nm, equivalent to 0.1 mu m. In plasma applications the instrument would have a sensitivity of n_eL approximately=2*10²⁰ m^-2, where n_e is the electron density and L the length of the laser cavity.

Optical setting on the profiles of reflecting objects, solids or fluids, by striascopic imaging with parallel laser light can be accurate to better than +or-1 mu m, if the optical system is calibrated with spherical and cylindrical gauges of 1-5 mm radius. Upon tenfold magnification the symmetrical central black fringe on the photographic image is at least 70 mu m wide. Parallel laser light is very convenient in aligning all optical elements and renders the object focusing non-critical to +or-1.4 mm. The gauge data show that the striascopic image is not formed by reflective interference alone but also by diffraction. The smaller the aperture of the three-dimensional optical filter, the more diffraction will participate and the more closely the centre of the central black fringe must approach the geometrical image position. The method is applied to profile measurements of mercury drops in aqueous solution and to nitrogen bubbles in water, with diameters of 5-9 mm.

Field desorption mass spectrometry requires ion emitters of reproducible high quality. A new method is described for producing field desorption emitters covered with carbon, metal or alloy dendrites within a few minutes. Their emission properties are as good as those of the well known carbon dendrite emitters produced at high temperatures.

A new very simple method of focusing an ion beam from a quadrupole mass filter has been devised. Using an electrostatic octopole lens it is possible to obtain narrow, high-intensity, low-energy ion beams suitable for use in beam studies of ion-molecule reactions. Only two voltages are necessary to focus the beam unless operating near the space charge limit. It was found that beam intensities and angles are limited only by space charge effects. The system is very much easier to operate than a magnetic sector mass spectrometer and retarding lens, and its performance is equal to and in some respects better than that of the magnetic sector.

Plastic scintillators commonly in use in the secondary-electron detectors of scanning electron microscopes are known to deteriorate rapidly, particularly under conditions of operation at high electron beam currents. A simple method is described for the production of scintillators from P-47 phosphor powder which is known to have excellent durability. The performance, evaluated in terms of the signal-to-noise ratio, detective quantum efficiency and relative light output, is correlated with the surface coverage of the phosphor layers, and compared with some commercial plastic and powder scintillators.

Details of the design and construction of an instrument for the direct measurement of skin friction on cylinders in an external gas flow are given. The use of the servo force-balance principle represents a valuable improvement on previous instruments because (i) the sensing element is held in a fixed position by integral (I) control, guaranteeing a constant local flow field, and (ii) the proportional (P) feedback can be used to increase the natural frequency of the system, thus allowing the accurate and sensitive detection of such dynamic features as vortex shedding frequencies. The use of velocity, or derivative (D), feedback instead of oil damping allows operation of the transducer in an arbitrary orientation. It is an important fact that the sensitivity of a force-balance system is independent of the PID settings.

An apparatus is described which is suitable for measuring self-diffusion coefficients in solids using the nuclear magnetic resonance spin-echo technique employing a pulsed field gradient. The design of the probe arrangement for use at high temperature (to 1300K) and the electronic circuit to generate the large pulses of magnetic field gradient are described in detail. The apparatus is designed for use with a pulsed NMR spectrometer assuming suitable timing pulses are available. The current switch handles 150 A, and the pulse has a fall time (to 10%) of 50 mu s and produces a field gradient of 1.5 T m^-1 in a quadrupole coil surrounding the high-temperature probe.

A recording gaussmeter was made using a high-resolution NMR spectrometer. The gaussmeter covered fields of 1.3-2.5 T with a sensitivity of 5*10^-8T. The instrument may be applied to susceptibility measurements by recording the additional fields due to the induced magnetisation of para- or diamagnetic material.

A controller for a superconducting solenoid magnet is described as an example of a microprocessor replacement for hard-wired digital logic in a research laboratory. Its purpose is to take control of the field-changing tasks, and other solenoid status functions such as the superconducting-normal transition. The relatively slow speed of this task is ideally suited to an 8-bit microprocessor, making available a larger data acquisition minicomputer for data processing while the microprocessor operates independently. The minicomputer presents the microcomputer with the desired field value and returns to data processing, while the microprocessor independently measures the present field value and ramps the solenoid power supply to the desired field value, signalling the minicomputer when this has been done.

In certain flow situations a particular visualisation technique has considerable advantages over all others; the authors suggest this is the case for cholesteric liquid crystals in film cooling. The cholesteric liquid crystal surface-temperature flow visualisation technique has been used as a back-up to conventional methods of measuring temperature and heat transfer.