Table of contents

A review is made of the development and performance. A simple theory necessary to understand the principles of operation is outlined. Characteristics such as gain, pulse height distribution, timing and long-term operation are summarised. Some general considerations concerning fabrication processes are presented together with a specific design of a detector array. A novel structure of a PPEM exhibiting self-scanning x-position sensitivity is also described. A general comparison with the channel electron multiplier shows that the two devices generally operate in a similar way but differ in saturation behaviour.

A simple method is described for determining the dielectric constants of small dielectric plates with an accuracy of about 1% at audio and radio frequencies. Guard rings, micrometers, insulating bushings, etc. are avoided. The lead and fringe capacitances are allowed for by extrapolating the measured capacitance to zero area of the dielectric plate.

Describes a method to measure the spectral reflectance and transmittance as functions of the angle of incidence. In this method the use of a standard reflector for comparison is eliminated.

A low-cost method is described of digitising an operational multichannel frequency-modulated analogue recording system by simultaneous counting of the number of cycles over the sampling interval. The observed resolution of 14 bits is improved by appropriate redesign of the telemetry.

Describes a reverse flow sensing hot-wire probe based on the principle of detection of the Karman vortex street in the near wake of a circular cylinder. Tests in a laminar separated shear layer point out the limitations of its use in practical situations due to the dependence of vortex shedding on Reynolds number.

The circuit described gives the frequency-independent phase shift for a band-limited signal, while keeping its amplitude invariant. The key component is a field-effect transistor which, driven by a frequency discriminator, provides a resistance which is inversely proportional to the frequency. A prototype circuit produces a phase shift flat to within +or-2 degrees over the frequency range from 20 to 40 kHz.

A compact and easily portable instrument is described which incorporates a needle probe thermal conductivity apparatus used in conjunction with a microprocessor to provide instantaneous values of thermal conductivity.

The 0.1 mu m thick window covers a 5 mm hole in a 0.1 mm thick copper disc coated with 0.1 mu m of glass. No sealants are used. The disc is mounted directly, together with a standard copper gasket, between the knives of the flanges connecting the lamp and an ultrahigh-vacuum system. The windows are bakeable to at least 300 degrees C.

This method is an improvement on the one used earlier by Bennet et al. A TEM₀₀ mode laser is used with an adjacent axial mode spacing of 640 MHz so that two axial modes which are polarised mutually orthogonally are sustained. The beam is passed through a rotating Polaroid to a photosensor. The modulated part of the photosensor response is extracted as an error signal by phase-sensitive rectification and converted into a suitable current which is then passed through a coil wound around the laser tube. The thermal control of the cavity length by the feedback current ensures the frequency stabilisation of the two modes. The degree of stability achieved, inferred from fluctuations of the error signal voltage, is found to be about 2 parts in 10⁸.

The instrument described is used to locate and study various noise sources and other disturbances, which would restrict signal perceptibility. From an analysis of these disturbances, the demands on apparatus components are estimated. Some constructional details are given, as well as suggestions for improvement aimed at a future interferometer of increased base length, with the prospect of successful operation.

A flash photolysis system, in which a very low-energy pulse of actinic light is highly correlated with the analysing light beam, is described. The performances of the system are exemplified by measuring, with a 3 ns time resolution, the singlet-singlet transient absorption signal of rhodamine 6G obtained with a 5 mu J excitation dye laser pulse and a non-pulsed 75 W xenon analysing light source.

A new ultrasonic meter is described which uses a linear spark as the source of the ultrasound pulse. Two quartz crystals downstream and upstream of the source act as receivers. The time taken by the pulse to reach the receivers is determined by the velocity and temperature of the gases. The flow properties at the intake and exhaust of an engine are measured using this meter.

A new type of thermostatic attachment to standard diffractometers allowing operations both above and below room temperature (-150 to +900 degrees C) and under vacuum is described. It has proved to be very useful in studying chemical reactivity and phase transitions owing to its simple assembly and great flexibility. The thermal expansion of sodium chloride is reported to illustrate the obtainable accuracy.

The stabilisation of a double-crystal spectrometer in a (+n, -n) position is described. A long-term angular drift of less than 0.02" has been obtained by means of a dynamic feedback system. This system has been especially devised for controlling the angle between the reflecting planes of the first and second crystal and thereby the position of the nodal planes of a standing-wave field created in perfect single crystals such as silicon.

A dilatometer is described in which the length changes of a thin wire are transmitted to a capacitive detector by a see-saw suspended on a phosphor-bronze leaf. The high-temperature anelastic deformations are determined by measuring the frozen-in length change after various annealing steps at a given low temperature. The samples are annealed within the dilatometer by self-resistance heating. It is found that the accuracy of the length determination is limited by the stability of the temperature distribution in the sample and in the dilatometer frame.

In the technique described a resistance strain gauge bridge is used. The output from the bridge is amplified and used to pulse-width-modulate a 20 kHz square wave. The modulated waveform is extracted from the shaft, using split brass rings and carbon-copper brushes, and demodulated to give a continuous record of shaft torque. In this way distortion of the torque signal by electromagnetic radiation and variation in contact resistance between brushes and slip rings is eliminated.

The convection cell described consists of a nematic liquid contained between two closely spaced parallel plates that are maintained at different temperatures. Sensitive circuitry detects any change in the cell capacitance and feeds back an AC voltage that holds the molecules at a constant angle and thus a constant capacitance.

An improved version of the Hesse-Rubartsch method is described. This method is applied, together with an adapted peak shape, to the evaluation of the hyperfine field distribution in an amorphous Fe_79.5Si_1.5B₁₉ alloy at room temperature. The detailed structure of this distribution is discussed.

A description of the program software written for the computer is given and methods are presented to enable both the sweep speed and vertical deflection factor settings of the sampling oscilloscope to be calibrated to a precision of greater than 0.5%. Details are provided of refinements made to the extrapolation method of time-referencing the data. The necessity of using a reference waveform and the advantage of using one particular configuration of the air lines in the coaxial line system are then discussed. Experimental details are given and it is shown that experiments yielding 50 frequency points can be performed typically in less than 17 min.

A new arrangement for five-pass interferometry is presented together with a holder for wavelength scanning and mirror alignment. The parallelism of the mirror surfaces can be controlled precisely through independent rotations around two mutually perpendicular axes and the distance between the mirrors can be varied by 860 nm independently of the angular controls. Necessary modifications in the design for scanning in other wavelength ranges are outlined.

Describes a discharge scheme for nanosecond excitation of high-pressure gases at temperatures of up to about 400 degrees C and specific power inputs of up to 1 GW cm^-3. The apparatus is used to observe the absorption and gain characteristics of dye vapour (Xanthene N-92) and metal halide (HgBr) plasmas respectively.

A description is given of a new method for absolute measurements of electron multiplier efficiency for electrons. The method, which is based on the use of a photoemission electron source and calibrated optical attenuation filters to control the electron intensity, has been used to measure the efficiency of a Mullard B419BL channel electron multiplier in the electron energy range of 40-1000 eV.

A new, simplified apparatus is described for fatigue-testing fibres using the technique of biaxial rotation over a pin. This involves the tension-compression of fibres which are rotated whilst bent over a pin. The angle through which the fibre is bent during a fatigue test can be altered, and the effect of this on fatigue life and fracture morphology are investigated.