Table of contents

Approximate expressions are obtained for the velocity resolution of Rudd's laser fluid-flow laser velocimeter when used with a spectrum analyser or with a pulse counting discriminator. The expressions are also valid for the several preceding variants of Rudd's scheme. The theory is supported by resolution measurements made using an analogue simulation of the velocimeter.

A fluid flow velocimeter is described that is suitable for recording velocity waves where the oscillation may be about a mean velocity of zero. The ambiguity between positive and negative velocities is not resolved but the magnitude of the velocity is recorded over a range of 30:1. The presentation allows the full waveform ranging from negative to positive to be easily visualized. Results are shown for waves of frequency up to 12 Hz and a peak velocity of 8.5 cm s^-1. Adaptation to other velocity ranges is straightforward. Linearity is 3% over the 30:1 velocity range. The improved dynamic range is achieved using a pulse counting discriminator preceded by a voltage tuned filter.

A number of techniques are described for obtaining polarization and excitation function data in the vacuum ultraviolet spectral region. These depend on the phenomena of resonance absorption and resonance fluorescence. Helium is considered in detail. The techniques are also suitable for the determination of the polarization sensitivity of vacuum monochromators.

The response has been measured of Kodak S.W.R. and SC-7 films and Ilford Q1 plates at 584, 736, and 920 AA and of SWR film at 1216 AA. The absolute values of the radiance were measured with a rare gas ionization chamber. The inertia was found to be the most useful measure of emulsion speed.

Measurements of extinction ratio, axis wander of the transmitted vibration over the polarizer aperture and ellipticity of the output beam are reported for various types of prism and sheet polarizers. The factors limiting the performance of the polarizers are discussed.

An electrometer has been developed which primarily is intended for measurement of electric fields associated with magnetically confined laboratory plasmas. The main features of the design are that sensitivity and time resolution have been significantly increased beyond the limits existing in present instruments of this type so that fields of the order of a few volts per centimetre can be detected, provided that fluctuations in the field have a time constant greater than a few milliseconds.

The calibration of an electromagnetic vortex probe is described, and the results are shown to agree with theoretical predictions. Some of the problems of such a probe are discussed.

A data collector for a coincidence experiment is described, which has been provided with a number of options not yet available in commercial instruments. The main features are: a bidirectional counter with controlled inputs, a freely adjustable number of channels, an automatic normalization on a monitor signal of the channel dwell period and a provision for 'lock-in' type measurements.

The study of rapid chemical reactions has been made possible especially by the ingenious method of chemical relaxation. The accuracy of the relaxation time measurement, however, depends critically on the signal-to-noise ratio which decreases with the reciprocal of the square root of the transmission bandwidth. In most cases, chemical relaxation signals can be repeated, superposed and averaged by adequate noise reduction equipment. Thus, one may determine the relaxation time with enhanced accuracy. Various types of noise reduction equipment are discussed and compared for an application in kinetic measurements in the second to subnanosecond range. The gain in signal-to-noise ratio improvement is normally of the order 20-50 but may attain values of 100-200 in extremely favourable cases.

The tensor permeability components were determined using circularly polarized microwave radiation, having established maximum allowed sample sizes from a study of the cavity perturbation conditions. It was shown that very slight departures from circular polarization markedly affected the results in the magnetically unsaturated state and electron paramagnetic resonance in a DPPH sample was used to set up the circular polarization very accurately. Examples of the data obtained for polycrystalline YIG at 9.3 GHz are epsilon '=15.2+or-0.3, epsilon "=0.009+or-0.001, mu '=0.91+or-0.02, mu "=0.003+or-0.0008, in zero field. In a field of 100 Oe, kappa '=-0.08+or-0.02 and kappa "=0.002+or-0.0003. The zero field losses are in agreement with calculations based on a natural resonance occurring at a lower frequency due to domain structure.

A mechanically triggered generator capable of delivering pulses up to 100 kV with subnanosecond rise-times in a coaxial system is described and oscillograms of typical pulses obtained with this generator are given. The pulses are generated by switching a spark gap, but it has been found that the second sharpening gap which has been used in previous switches employing this technique is not necessary with this arrangement. The design and results of a resistance divider, used to attenuate these pulses, is included.

An X-ray source with demountable anodes of three different geometries determining the angle between the electron beam and observation axis, is described. According to the form of the target chosen the tube is suitable for continuum, characteristic emission band, or weak emission line studies. In this wavelength region the continuum intensity is found to vary as the square of the excitation potential but is not proportional to the target atomic number. The number of photons produced per milliampere at a given excitation potential is given for the CuL alpha emission. An electron beam current of 500 mA is produced at 3 kV.

A modified magnetic tape head is used as a test specimen in the reflection electron microscope. The stray field around the gap changes the electron trajectories in the vicinity of the head and causes an apparent rotation of the object with respect to the direction of incidence of the electrons on the face of the specimen. A mathematical model is developed which accounts for the observed effects in a satisfactory manner.

An all solid-state automatic self-locking n.m.r. gaussmeter is described covering a magnetic field range of 2700-4000 G. The introduction of integral control reduces the static error and avoids the use of mechanical links. Sweep rates of up to 100 G s^-1 can be followed. An automatic search-lock circuit is also provided. The instrument has been used in precise magnetic field calibration for e.s.r. experiments.

The description of an apparatus specially built for torsion tests is presented. The design allows for rapid and accurate positioning of specimens, testing at different temperatures as well as for temperature changes during a test, and freedom from axial constraints. The instrument is constructed so that it can be driven by a testing machine of the Instron type so that advantage can be taken of the versatility of the latter. As a result, instantaneous changes in torsional deformation rate as high as 250:1 are possible. Reversed loading is also possible so that the Bauschinger effect also can be studied. Several references to torsional deformation work are included.

An ion source designed for the study of zinc isotopic abundances is described. A significant improvement in the ratio of signal to background has been achieved. The source is particularly suitable for medium resolution mass spectrometers.

A method is described whereby a vibration-displacement transducer system can be calibrated. The method is valid not only for amplitude calibration but also for phase calibration-this being the particular merit of the system. A phase coherent primary transducer is used employing a pair of silicon photocells. Itis shown that the proposed method gives repeatable and accurate results for a particular capacitive system. It is anticipated that equally reliable results could be obtained for other capacitive and inductive systems.

Three shutters for protecting optical windows from deposits are described.

A 360 degrees digital shaft rotation display unit is described for application to systems involving stepping motor, optical fringe or gap counting techniques. The unit responds to pulses which either cause or are derived from positive or negative rotation. The display operates in both forward and reverse sense through the 0/360 degrees setting, and provision is made to enable initial settings to be entered manually.

The furnace is for heating small samples to a known temperature in an inert atmosphere where the time taken to get to and from this temperature needs to be short. Samples can be treated in rapid succession at different temperatures with a precision of 1-2 degC, up to at least 700 degrees C.

A method is described for designing a single mode CO₂ laser cavity of high Fresnel number which oscillates in the fundamental transverse mode and a single longitudinal mode. A short, large bore cavity was constructed which oscillates in the TEM₀₀ mode without the use of intracavity irises. The radii of curvature of the reflectors were designed using the Gaussian beam equations of Kogelnik and Li and an experimentally determined mode selection parameter.

A small (2 mm diameter) fast (time constant=1.5 mu s), shielded pitot pressure transducer is described, and examples are given of its use in a high enthalpy shock tunnel.

Two infrared cells are described. The first enables rapid exchange of the powdered samples and thorough cleaning of the inside of the cell after treatments with adsorbates which contaminate the system. The second allows high temperature pretreatment of the samples in a controlled flow of gas.

The construction and performance of a simple spectrophotometric cell for measurements in the visible and ultraviolet region at elevated temperatures is described. The cell is small enough to fit into most commercial spectrophotometers and is designed for use with aqueous solutions up to 280 degrees C. The materials in contact with the solutions can be changed to those best suited for the experimental conditions.

A control unit, constructed from integrated circuit logic units, is described which will generate waveforms necessary to control experiments with colliding charged-particle beams. The unit will produce the most elaborate waveforms so far used in this type of experiment and it can be modified to produce the simpler waveforms which suffice for a number of experiments. All waveforms are derived from a single train of input pulses so that no subsidiary timing circuits are employed. The circuit is an order of magnitude smaller and less expensive than those previously used.

A furnace has been designed to allow small specimens to be bombarded in accelerators to temperatures up to 1400-1500 degrees C. It has a fast time response. Ion beam currents are measured by scanning the beam on to a peripheral collector which is not subject to significant stray currents from the heater.