Table of contents

This paper reviews progress in developing solid-state type transducer materials and compares the properties of those that have proved most successful in modern applications. Recent improvements in composite materials, as well as newly discovered piezoelectric single crystals and thin-film transducer materials are covered.

In laser interferometer measurement systems, changes of signal level may affect the reliability of electronic fringe counting. A circuit is described which compensates for changes in the signal level while the interferometer counting frequency is high, and which 'remembers' the average signal level when the counting rate is slower than a preset value.

Equipment capable of measuring attenuations well in excess of 100 dB at 10 GHz is described. Frequency shift modulation is used and the relative merits over conventional systems are discussed.

This note points out the applicability of the formula h=p/2M sin omega relating vertical distances h in the sample to parallax p and tilt angle omega , when an arbitrary (not horizontal) axis is used for the rotation (tilt) of the sample between exposures of left- and right-hand plates. Such an axis is usually required with crystalline samples, and may often be desirable with amorphous samples. It also indicates how the photographs may be correctly set up on the stereo viewer and the angle omega calculated, without recording or measuring diffraction patterns, if a calibrated goniometer stage is available, and presents in a simple notation and without approximation the correction required if the parallel projection approximation is not to be made.

A simple adaptor is described for attaching a small goniometer head to a diamond blade saw in order to pre-orient monocrystalline specimens by X-ray techniques and subsequently cut them along a selected orientation.

A simple voltage regulator with a 50 mu W quiescent power drain is described. The 5 V output changes by less than 0.1% over an input voltage range of 6.5-9 V and an output current range of 0-1 mA. Temperature compensation is included. The unit appears ideal for low power field instruments.

A convenient method for interferential spectral analysis is described. The results obtained are in agreement with the expected linearity of the apparatus.

The sample changer was developed for use in association with a 60 cm³ Ge(Li) detector connected to a 4000-channel analyser, which is used in the analysis of geological samples. The irradiated sample (in powder form) is sealed in a quartz vial contained within a polyethylene capsule. The transportation of capsules to and from the counting station is done pneumatically and is electronically controlled. Careful design of the counting station has reduced the counting errors considerably and the sample changer, which has been in successful operation for a year, permits maximum utilization of the detector system.

A simple method of filling water triple-point cells is described. The triple-point temperatures of cells prepared in this way were found to differ no more than 0.1 mK from the temperatures yielded by cells used in this laboratory for reference purposes.

An ion gun is described which operates in a relatively high pressure of argon ( approximately 0.1 Torr). In operation, the voltage across the discharge region of the gun is 500 V, but subsequent ion-atom collisions in the spectrometer sample chamber reduce the ion-atom energy to about 0.1-1.0 eV at the sample surface. By operating in this mode, as distinct from high vacuum/high voltage (2-5 kV), the ion beam is dispersed and its energy is insufficient to cause structural damage to the sample surface, but sufficient to remove adsorbed species. The photoelectron spectra of a Cu-Zn alloy (brass) and of mild steel are given and illustrate the gun's cleaning capability.

A cheap and simple waveguide termination is described, for thermal calibrations in the frequency range 2.65 to 2.75 GHz, for all temperatures between 77 K and ambient. An important feature of this termination is the very compact microwave absorbed configuration which is in intimate thermal contact with the coolant. The uncertainty in the effective noise temperature of the termination is consequently small.

The behaviour of hot-film anemometers in helium-air and argon-air gas mixtures is reported. Cylindrical parabolic and single-ended sensor geometries were examined. Unlike that of uncoated hot-wire anemometers, the behaviour of quartz-coated hot-film anemometers is only weakly influenced by the 'thermal slip' effect that is produced by a poor thermal accommodation coefficient between the gas and the hot sensor. The cylindrical sensor oriented with its axis normal to the flow is recommended for most applications. However, for dirty flows the parabolic sensor should be used.

A study of the kinematics of moire fringes produced by moving line gratings relative to each other provides an explanation for optical phenomena appearing during the motion. A method of determination of the instantaneous pole of relative rotation of the gratings is further derived.

The properties of a helium atomic beam formed by a fused glass focusing array of about 10⁷ capillaries each 5 mu m in diameter and 2.5 mm long, the axes of which are directed to a point 50 mm from the array have been investigated. The axial atom density and the total throughput are consistent with Zugenmaier's theory for a single capillary. The beam halfwidth is anomalously six times wider than expected theoretically, but it is shown that this is not primarily due to a constructional error in the array. An axial helium density of 10¹⁴ atoms/cm³ at a beam width of 5 mm was obtained at an input pressure of 2 Torr, with a total helium throughput of 1.5*10¹⁹ atoms/s.

The sample is connected by a finite thermal resistance to a large capacity heat sink, suitably enclosed by an outside shield. Equivalent circuits of such a calorimeter system with a sample of high or low thermal diffusivity are analysed. In both cases relations are given for the accurate evaluation of the latent heat from the temperature difference measured between the sink and the sample during a phase transition. The analysis also helps to determine the optimum performance of the system which includes linear heating of the sink with the above difference constant away from the transition. The correct interpretation of superheating and supercooling effects is also included. This method has been used for latent heat measurements of liquid crystal phase transition.

A wide range, precision falling sphere viscometer is described. Sphere fall velocity was determined photographically to avoid operator sighting and timing errors using a 2 cm measuring interval. With this apparatus fall velocities from 0.01 to 40 cm s^-1 were routinely determined with a repeatability of +or-0.2%.

A flow photometer which is capable of measuring simultaneously the light scattering and fluorescence of stained mammalian cells is described. An argon-ion laser serves as the light source. As individual stained cells cross the laser beam, a scattering and a fluorescence light pulse are produced. These signals are detected, amplified, and subjected to pulse-height analysis. In its simplest form, this instrument is used to gate one signal by the other, thus extending the sensitivity of the flow microfluorometry techniques developed at the Los Alamos Scientific Laboratory. Data are presented illustrating the capability of the instrument to extract the signal from the noise, in the case of weakly stained cells, and to distinguish cells in a mixed population based on a combination of these two parameters.

A stopped-flow system was designed which allows precise control of flow variables during chemical generation of free radical species in the cavity of an ESR spectrometer. This equipment is applicable to both continuous and stopped-flow studies. It may be used to determine the kinetics of disappearance of short-lived intermediates with lifetimes in the millisecond range. The capability for the generation of accurate kinetic data is provided by the usage of rapid-action solenoid valves. A method for measuring their response times is described. Other features include components for oxygen and temperature measurement and an automated system for triggering repetitive kinetic experiments in conjunction with signal-averaging techniques. The advantages and improvements of this stopped-flow technique over previous such methods are discussed.

Optical losses introduced in a He-Ne laser cavity by a BSC glass window around the Brewster angle have been estimated. Absorption losses within +or-45' of the Brewster angle are found to be nearly constant and predominantly large compared with the reflection losses. Contrarily, the presence of skew angles increases the reflection losses which become comparable to the absorption losses at a skew angle of about 30'.

A simple optical system for photomixing is developed by making use of a suppressed-carrier amplitude-modulated ultrasonic wave. Both the sideband components in the first order of the diffraction spectrum of light act as the signal and reference waves in photomixing. The superposition of these components at a photodetector yields a beat signal operating at twice the modulation frequency. For the superposition of the signal wave with the reference wave, a self-aligning optical system is realized. The speed of sound is successfully measured from the phase increment of the heat signal. The measured results in water and in the mixture of water with methanol are in good agreement with previous workers' data. The phase change due to the speed of sound varying with temperature in water is further detected in a real-time manner.

A simple vibrating sample magnetometer, operating from 4.2 to 300 K, has been developed. The sample is forced to vibrate vertically with a fixed frequency and amplitude, as is usual for this type of magnetometer. The vibration is obtained through an electrostatic excitation of a resonance mode in a high Q mechanical vibration unit. Supplied with 'perpendicular' detector coils, the instrument is very suitable for accurate determinations of both high and low magnetic anisotropy.

An outline is given of the basic principles of a new method for loading multiple samples into a field ion microscope which allows sequential examination of the samples without loss of cooling or degradation of vacuum. Two operating systems are described; a liquid nitrogen cooled, glass high vacuum microscope with a four sample capacity and a liquid helium cooled, all metal ultrahigh vacuum microscope with a five sample capacity.

A design is presented for a LEED (low-energy electron diffraction) apparatus in which diffraction patterns are to be displaced by a uniform magnetic field, so that they are not masked partially from view by the electron gun or by the target crystal. Two useful features of the conventional field-free design are retained: diffraction patterns can be displayed (i) with high angular fidelity and (ii) with little background from electrons which have scattered inelastically in the target crystal. Both features derive from the shape of the display screen and of its enclosed system of concentrically nested electrostatic retarding grids. The shape resembles that of an American football and permits all elastically scattered electrons to enter the grid system at the same angle of incidence regardless of their points of entry.

The Thorn image-retaining panel is used in a spectrograph to produce luminescence spectrograms with no development process. The image can be printed on to a Panchromatic plate for a permanent record, and examples of discharge lamp spectra are reproduced. The resolution of the panel is 8 line pairs/mm and it is generally less sensitive than a photographic emulsion, but its wavelength response extends to 1.5 mu m.

A refractometer has been constructed which is capable of measuring refractive indices of infrared transmitting materials to an accuracy of +or-0.0001. Samples are used in the form of Littrow prisms and a precision goniometer incorporating a radial moire grating provides the method for angle measurement.

The press has an oil-driven piston which is free to tilt, the oil being retained by a rubber diaphragm rather than by O rings. It consistently produced less than 15% difference in strain between opposite sides of a uniform cylindrical sample. Two presses of this design were used in extensive experiments on the effect of uniaxial compression on the magnetization of rock. Both presses were used with astatic magnetometers and hence had to be made of nonmagnetic materials-aluminium alloy and phenolite. The presses permitted measurement of stress-induced magnetization changes as small as 1/10% of the initial magnetization or 5*10^-6 emu (whichever was the greater).

An approved electronic detection system for Auger spectroscopy is described which may be used with two, three or four grid conventional display low energy electron diffraction systems. Amplifier noise in this arrangement is reduced so that it is comparable to the shot noise due to 1 mu A electron beam. The improvement in the Auger signal-to-noise ratio allows a much reduced time constant in the lock-in amplifier and hence a faster scan rate.

A method is described for producing microneedles on field anodes. Field pyrolysis of benzonitrile causes the growth of these needles at a temperature of about 1200 degrees C. They yield optimal emission qualities for field-ionization and -desorption mass spectrometry. The needles prove to be resistant to chemical attack as well as thermal and mechanical stress.

This paper demonstrates the use of transmitting diffraction gratings as beamsplitters in an oblique incidence interferometer and the application of that interferometer to measuring the flatness of non-optical surfaces. Many different surfaces have been examined, ranging from lapped granite and steel to unworked metal and processed photographic emulsions. The fringe interval in the interferograms is independent of the illuminating wavelength, being one half of the diffraction grating periodicity, which in the interferometer described is 5 mu m. It is also demonstrated that the topography of large surface areas may be evaluated by the combinations of interferograms.

An apparatus is described which has been developed to measure the change in absorption of submillimetre radiation by a disc specimen on application of a high pulsed magnetic field. The absorption spectra of doped (p-type) germanium specimens have been measured up to a field of over 20 T, using a 337 mu m (891 GHz) gas laser, and show cyclotron resonance of the light and heavy holes.

Three problems which have arisen in the use of an interferometer for calibrating Mossbauer spectrometers are (i) mode jumping in the laser, (ii) the digital nature of the signal, (iii) a problem due to the asymmetry of the signal about the mean level. These are discussed, and solution proposed.

In the spectracon image tube photoelectrons from an input photocathode are accelerated through 40 kV and focused to form an electron image at a mica window. The window is strong enough to withstand atmospheric pressure, but allows transmission of 75-80% of the incident photoelectrons. In the usual mode of operation, these electrons are recorded in a nuclear track emulsion and the resulting electrographs may subsequently be analysed. Principally because of the spread in the number of developable grains produced by each photoelectron, the signal-to-noise ratio obtained by this method is lower than it would be if all electrons were registered with equal weight. This note describes a system which is designed to achieve maximum efficiency by recording each transmitted photoelectron as a single count.