Table of contents

Metrology and process measurement sensors for use in the aggressive conditions within nuclear reactors in general, and within liquid-metal-cooled fast reactors in particular, are outlined. Materials and constructional techniques suitable for high temperatures are discussed. References are made to sensors for strain, displacement, pressure, temperature and flow measurement in the 300-600 degrees C range of ambients, more especially to less well known designs.

A low-cost microprocessor-controlled heater for the study of thermoluminescence is described. This system enables a programmed nonlinear heating profile to be used to facilitate glow curve analysis. The apparatus was constructed for a research study concerning the dating of ceramics by measuring thermoluminescence (TL) induced by natural sources of ionising radiation. The use of microprocessor control gives the instrument a flexibility not available to hard-wired systems, and has great potential for further development.

A two-stage Gifford-McMahon refrigerator has been modified to be UHV compatible. It can thus be baked without the expansion mechanism being disassembled. A description is given of the cold head used to cool samples down to 40K in UHV with a fully manipulable sample holder.

A backscattered electron detector for use in a scanning electron microscope has been constructed using a europium-doped calcium fluoride single crystal. It has been shown that the detector is very suitable for examining uncoated insulating materials and has been applied to several materials such as ceramic and human tooth dental enamel.

It is shown that the imaginary part of the dielectric constant can be uniquely, simply and directly determined for a thin (nd<< lambda ) but strongly absorbing film on a transparent substrate. The measurements required are the film thickness, the transmittance and the reflectance from the substrate side.

A coaxial line system is described which enables the complex permittivity of solid tissues to be measured accurately at spot frequencies between 2 and 18 GHz. The design and constructional details of the cell are given. Various sources of experimental error are considered and test data are presented.

An original coupling model is presented for a classical helical resonant cavity having good matching in the entire range and eliminating the parasitic lambda /2 resonant modes. A new cavity design using microstrip techniques and this original coupling mode are then described. The results from experiments performed on the cavity are given and discussed. These include: eigenfrequencies, quality factor and coupling at all frequencies in the band.

A fluorescence detection system, consisting of five scintillation detectors has been commissioned on the first EXAFS Station, 7.1, of the Daresbury Synchrotron Radiation Source (SRS). This system measures the X-ray absorption spectrum by recording the X-ray fluorescence excitation spectrum of specimens containing a small number of metal atoms with absorption edges between 0.1 nm and 0.31 nm. The present fluorescence system, its increased sensitivity over absorption, and the present detection limits are described.

The construction of three high-pressure optical cells of simple construction and large volume (30, 110 and 550 cm³) is described, the total cell content being observable in the 30 and 110 cm³ cells. In conjunction with a simple metering, stirring and heating system, the cells permit rapid and precise measurement of phase equilibria up to 200 MPa (30 cm³ cells) and 100 MPa (110 and 550 cm³ cells) and up to 350 degrees C, according to the synthetic method, without additional analytical effort. Using the 550 cm³ cell, the dew points of very sparingly volatile substances can be determined up to concentrations of 0.01 kg m^-3 with a relative error of about 0.05. The validity of the experimental technique has been tested on known systems, and excellent agreement with literature values has been obtained. The solubility of methane in cyclohexane has been measured at 37.8 and 71.1 degrees C and up to about 18 MPa.

Using the technique of capacitance micrometry it is possible to measure very small displacements. The authors describe the application of this technique to the control of piezo-scanned Fabry-Perot etalons using a closed-loop feedback system. This system removes the problem of the nonlinear response and hysteresis associated with piezoelectric transducers and allows precise control of both etalon gap and parallelism.

A method, based on laser Doppler techniques, for measuring macroparticle velocities and emission rates in vacuum (metal vapour) arcs is presented. A real-fringe forward-scattering system was employed, excited by a He-Ne laser, producing an ellipsoidal probe volume. Time domain analysis of individual scattering events was used to determine the macroparticle velocity components, while counting of the individual events was used to yield macroparticle emission rates. The experimental method enabled a study of macroparticle dynamics as a function of space and time in pulsed vacuum arcs of 1 and 2 kA peak current, 5 and 30 m s^-1 duration, sustained between 12-14 mm electrodes, spaced 4 mm apart and fabricated from either Cd, Zn, Al, Cu, or Mo. Broad velocity component distributions, ranging from about 10 m s^-1 up to about 800 m s^-1, and dependent on cathode metal, arc current waveform, time after arc initiation and spatial location in the discharge volume, were measured. The macroparticle emission rate was found to reach its peak a few milliseconds after the occurrence of peak current.

Directional responses of hot-wire probes are studied experimentally, and a theory is developed which attributes pitch response to aerodynamic disturbances caused by the probe and yaw response to a combination of aerodynamic disturbances and heat transfer effects. The predicted cooling velocity has the same form as Jorgensen's equation, and the pitch coefficient, predicted in terms of the probe geometry, compares favorably with experiments using ideal probes. Comparisons with real probes indicate the limits of validity imposed by hot-wire probe tolerances. The accuracy of Jorgensen's equation for combined yaw and pitch has been measured experimentally.

The electronic circuit associated with each X-ray detector in the front end of a computerised tomograph must fulfil very stringent requirements concerning its dynamic range, accuracy and noise contribution. Starting from input signal considerations under extreme conditions, those requirements are analysed and the use of a scintillator followed by a Si photodiode is considered. A novel circuit approach using an optocoupler for range switching between two integrators is adopted, that meets all the requirements. A prototype, with a built-in calibration circuit and associated logic, was built and tested for dynamic range and noise performance. The results were compared with those expected from the design calculations and found to be satisfactory.

A broadband (25 MHz) waveform-recording system yielding a high voltage resolution (10 nV range) by signal averaging is described. It consists of a transient recorder Biomation 8100 coupled to a PDP 11/04 computer via a CAMAC I/O-register NE 9066 supported by an appropriate software system. Some applications of the measurement system are indicated.