Table of contents

Phase sensitive detection is formalized in order that its operation can be understood and its practical use optimized. The theory explains how narrow bandwidth amplification is achieved in order to reduce the noise content of a measurand and how the process can be considered simply as a multiplier followed by a low-pass filter. The responses to various excitation and measurand forms are derived for signals ranging from the simple sinusoids to the more complicated signals produced when modulating interference fringes and stabilized laser cavities.

The standard bias-temperature test was performed to study the effect of HCl gettering on ion drift instability. It was found that though HCl gettered device was free of ion drift instability, it introduced another type of instability called trapping instability to the device. Lack of the reproducibility of the original curve after deplorization was also observed.

The application of a pin photodiode as a detector of electrons with energies above 100 keV is explored. Current densities down to 20 mu A cm^-2 are detectable. The response time is shorter than 4 ns.

A spark cutting method using a stationary and a rotating disc has been developed for preparation of spherical samples. Maximum deviations from a perfect sphere of less than 0.1% can easily be obtained for samples with a diameter of 1-3 mm.

A bridge circuit is described which provides a compensating voltage for easy leakage adjustment of crossed coil NMR probes.

A position sensitive counter with high spatial resolution is described for use in low angle X-ray scattering studies from live muscles. The main sources of spatial noise are evaluated to enable the design of the counter which has a spatial resolution of 100 mu m (FWHM), an efficiency of 85% for the detection of 1.54 AA X-rays and requires a gas flow of only approximately 10 ml/day to maintain suitable operation.

A circuit was built to gate a photomultiplier containing a focus electrode in the nanosecond timescale using avalanche transistors. The circuit design and performance are described together with precautions that were taken to obtain fast switching speeds. This method is applied to single shot procedures, where fast luminescent signals are being studied.

Using a commercial d.c. voltmeter, a current supply for a superconducting magnet with a stability of a few parts/million can easily be built. A slow sweep mode is also included in the feedback circuitry.

A simple technique has been developed which enables the examination of any uncoated insulating specimen in the scanning electron microscope at high accelerating voltages without intensity fluctuation charging artefacts. The specimens were placed in the specimen chamber which had been modified to contain a small residual water vapour environment, and were imaged using a wide angle backscattered electron detector. It would appear that the presence of the water vapour sufficiently reduced the resistance of the insulator so that any charging which may have occurred was not detected by the backscattered electron detector.

An experimental technique is described for the use of high resolution mass spectrometry in the determination of activities and heats of sublimation. It is shown that experimental difficulties due to interaction of permanent gases (CO, Ar, N₂, H₂ and He) with metal vapours (Fe, Co, Cr, V) can be overcome. Second law heats of sublimation are given for vanadium, chromium, iron and cobalt which agree with literature values obtained by different methods.

In nonisothermal transport of sorbable gases through thin microporous membranes of large cross section, temperature gradients across the membrane faces should be avoided. A diffusion cell has been constructed meeting this requirement. This, with associated equipment, allows one to investigate isobaric flow and thermo-osmotic steady states or single gases for for mixtures, and to measure mixture separation.

The apparatus is described in detail, and compared with existing units. Its high precision possibilities are discussed. A sample experiment was performed using CO₂ and 30 keV electrons; the total scattered intensities are presented for the range of s from 0.45 AA^-1 to 32 AA^-1, where s is the classical electron diffraction parameter. The normalisation technique is discussed; and the results are compared with previously published measurements. The difference function obtained by comparison with the predictions of the independent atom model shows doubly shaped oscillations, which are not due to experimental error.

The Merrifield process for the synthesis of polypeptides involves a very large number of successive steps. A circuit is described which provides automatic control for these processes and allows a particular sequence of amino acid residues to be predetermined. The circuit depends on solid state devices and switches and thus has a high level of reliability. Although designed for a specific purpose the circuit is readily adapted to many applications where control processes involve repeated, sequential operation of a cyclic nature.

The instrumental lineshapes of polaritons observed in near forward scattering experiments with the arrangement suggested by Claus have been calculated by means of geometrical optics. The width of the exciting laser beam, the finite apertures of blinds and the acceptance angles of lenses have been considered. The results are compared with experimental lineshapes of a phonon polariton in uniaxial potassium bromate.

The calorimeter used as the primary standard for 0.4-1.1 mu m pulsed laser measurement at NPL consists of a Ni/Cu cone with heating coils and resistance bridge sensing coils around the whole outer surface. An automatic measurement of the light reflected from the cone is made on each shot. The major source of systematic error lies in establishing the difference between the output from a calibration pulse and the output from a laser pulse. Computer modelling of the heat flow was used to predict this difference but still left a residual uncertainty of 0.5%. The overall systematic error at 30 mJ level is +or-0.52% with 0.15% statistical error (SEM over six shots).

Some methods of estimating the damping factor delta are discussed. A simple electronic device is described, which is applied to the automatic determination of the internal friction-temperature characteristic of a martensitic sample at a low frequency of oscillation. Each value of delta is determined by the free decay technique. The consistency of the results shows the remarkable accuracy of the method, although the ratio of the initial to the final amplitude during each decay was not more than 1.2. Thus internal friction can be measured at a nearly constant amplitude of oscillation.

It is shown that the beam tilt circuitry of an electron microscope may be used to determine lattice constants. The method has certain advantages over the usual techniques of photographing diffraction patterns: it is rapid, measurements are not affected by choice of accelerating voltage or camera constant and the effects of lens aberrations effectively cancel. Interplanar spacings may be obtained to within +or-0.1% for polycrystalline samples. Single crystal samples permit spacing determinations accurate to +or-0.06% and interplanar angles to +or-0.05 degrees .

The design principles of a 24 in diameter interactive display system are discussed, the display being refreshed from a buffer. This part of the design is quite general. Its particular use when attached to the department's 'POLLY' bubble chamber film measuring device provides a new facility that should be of great value with difficult film. It could also provide a far greater flexibility of scan pattern for POLLY than can be obtained by other techniques. The principle of a video data set which is introduced can be applied to any of the CRT scanning devices currently in use.

Details are given of a directionally sensitive laser anemometer which may be used for the measurement of highly turbulent liquid flows. Directional sensitivity is obtained using a simple and inexpensive acousto-optical cell as a frequency shifting device. The accuracy of the anemometer was checked in two relatively simple flow situations and the instrument was then applied to the measurement of mean velocity and turbulence intensity in a complex turbulent recirculating flow.

The thermistor bridge is described. The relative pulsed deposited dose may be measured with a reproducibility from shot to shot of approximately 5%. The absolute dose measured is consistent with that measured by LiF thermoluminescent dosimeters in a 4 MeV bremsstrahlung spectrum if photon absorption and electron scattering are fully taken into account.

An apparatus for measuring the conductivity of solid and molten polymers from room temperature to 250 degrees C is described. 'Edge effects' are eliminated by enclosing the heat source and samples inside the heat sink, hence guard rings are not used. The heat flow is three dimensional and the conductivity is obtained by a numerical calculation. Two disc shaped samples 48 mm diameter by 2 mm thick are required. Some typical results are given.

The relations governing image illuminance and fringe contrast in hologram interferometry have been studied for a hologram camera and display system designed for the use of low resolution imaging devices. The most suitable aperture is a double slit. The efficiency of the filtering geometry introduces an inverse relationship between attainable interferogram fringe contrast and necessary exposure time in the recording step. Criteria for material and system assessment are derived. The study is exemplified by measurement series on recordings on a 35 mm microfilm using three types of apertures.

A technique has been developed for directly measuring the amount of surfactant, which is suitably labelled with a ¹⁴C atom, adsorbed at an oil-water interface. The technique entails using an oil-soluble, non-surface-active scintillant and a photomultiplier. The number of pulses detected is proportional to the ¹⁴C surfactant concentration at the interface and after suitable calibration this can be transformed into the surface concentration. As an example, the technique is used to measure the adsorption isotherm for cetyl-1-¹⁴C-trimethylammonium bromide at the toluene-water interface.

The vertical and horizontal components of fluorescence emissions are recorded simultaneously by means of a Wollaston prism. Hence rapid changes in fluorescence anisotropy can be followed. Experiments with the isolated electroplax of Electrophorus electricus are described.

Describes how an argon ion gun intended for sputter cleaning, and a quadrupole residual gas analyser (QRGA) have been adapted for use in low current, low energy secondary ion mass spectroscopy (SIMS). Minor external modifications including the fitting of a new type of axial electrostatic energy filter in front of the QRGA make secondary ion detection feasible. The spectrometer may be used for surface analysis; secondary ion spectra are presented from stainless steel type 316, and from mica and sapphire.