Table of contents

A brief report is given of the 12th International Colloquium of the AMPERE Group which was held at Bordeaux from the 17th to 21st September 1963. The Conference at Bordeaux was concerned in particular with electron spin resonance and investigations of solid dielectrics, while the Conference next year at Louvain will be concerned with nuclear resonance and liquid dielectrics.

The papers presented at the Conference were of two types, there being eight general summary papers in which various aspects of research were covered and over one hundred short communications which covered all aspects of the electron resonance and dielectric fields.

A torque meter is described which employs the principles used in work with resistance strain gauges to convert small torques developed in isolated specimens directly into electrical signals. The overall sensitivity and the maximum torque that can be measured with this meter can both be altered appreciably by suitable modifications in design, but for the instrument described the overall sensitivity is about 3 dyn cm per cm deflection and the maximum torque is approximately 4 × 10³ dyn cm.

The meter has been used to measure the anisotropy torque developed in a (111) single-crystal disk of nickel and hence the second magnetocrystalline anistropy constant K₂. At 23° C the effective values of K₂ appropriate to 7300 Oe and infinite field are respectively 2.38 × 10⁴ and 2.53 × 10⁴ erg cm^-3. These results are in excellent agreement with the direct determination of K₂ for nickel by Sato and Chandrasekhar.

An electronic method for the measurement of thickness and deposition rate of conducting films during a vacuum evaporation is described.

Operational amplifiers are employed to monitor the change in resistance of a deposited layer and their outputs used to servo control the deposition rate and automatically cut off the vapour stream when the deposit has reached a predetermined thickness. The equipment allows close control of the deposition rate and thickness, thereby increasing the uniformity of deposited layers during successive evaporations.

The paper outlines the design of a simple electron beam machine giving an electron spot of a few micrometres diameter. It is shown that the power density achieved approaches closely the theoretical value; in particular a power density of 25 MW cm^-2 has been measured in a 2 μm diameter spot at 60 kv.

Examples of some of the initial applications of the machine are also given.

A gauge has been designed to determine the gas density in blast waves by recording the attenuation of β-rays from erbium-169 using a compact detector unit and transistor amplifier. The output signal is transmitted over several thousand feet of coaxial cable and recorded as an f.m. signal on magnetic tape. Voltage and density calibration units are described. The gauge has been used to study blast waves in the 60 to 5 lb in^-2 over-pressure region, and some results are presented. The present accuracy of about ±10% may be improved by using a source of greater activity and by strengthening the mounting system to prevent slight changes of the source-detector geometry.

From the ratio of the collector currents of two ion gauges operating under identical conditions, the coefficient of secondary electron emission by positive ions for one collector can be deduced if that for the other collector is known. Changes in the coefficient, owing to oxidation of one collector surface for example, can also be followed provided the reference surface remains unaffected. Some results relating to the oxidation of molybdenum are included using molybdenum oxide as the reference surface.

In response to the need for closer control in direct-stress electrical breakdown investigations in dielectric liquids, an improved test method has been developed. A high-voltage power supply is arranged to give an output voltage which is a slow, linear ramp function of time. The voltage is reset automatically on breakdown, and a recorder and thyratron by-pass circuit complete an automatic system which is capable of making the large number of closely controlled measurements needed for a statistical study.

An instrument is described with which the velocity of a slowly moving fluid can be determined in terms of the change in temperature of a heated copper body exposed to the fluid stream. The change in temperature is detected by a thermopile assembly whose output is recorded on a spot galvanometer. The useful range of the instrument for the measurement of water velocity is 0.1-1.0 ft sec^-1 and for air velocity 1.5-15 ft sec^-1.

The reduction of the winding space in a superconducting magnet is an important design consideration. The problem of a design for a Helmholtz pair, based on the field at the centre, the current density and the coil separation, can be completely specified using this minimization criterion. The mathematical equations are solved numerically, and, after reduction to a non-dimensional form, the results are presented in a table.

A new millimetre wave magnetic resonance spectrometer, using broad-band components, is described. A `magic tee' provides both a balanced harmonic generator and a detector of the harmonic signal which has passed through the sample in the spectrometer. Studies have been made of a simple reflection system with no resonant cavity at about 4.7 mm wave-length, using standard 8 mm components. With a power of about 30 MW incident on the harmonic generator crystals, a time constant of 1 sec and a magnetic field modulation frequency of 630 c/s, approximately 9 × 10¹⁵ paramagnetic spins of 1 gauss line-width can be detected. The device is primarily intended for antiferromagnetic resonance studies and is in principle capable of operating at much shorter millimetre wavelengths.

Strain in a moving bar has been measured without the need of external connecting wires. Changes in resistance of a silicon strain gauge, which forms part of the bias circuit of a small tunnel diode transmitter, mounted on the bar, frequency modulate the carrier. The signal is received by a conventional f.m. communications receiver, the output of which operates a chart recorder.

It was found that, under certain conditions, a more accurate measurement of substrate surface temperature was obtained by using thin-film copper-nickel thermocouples vacuum deposited directly upon the surfaces of glass substrates than was obtained by using conventional wire-type thermocouples.

The present paper describes an electronic stress-reversing device for the Hitachi H.U. 11 electron microscope which combines the advantage of variable fatigue rates with the ability to select various strain amplitudes. The device, when coupled with the standard Hitachi tensile deformation attachment, will apply a controlled zero-tension stress to a thin metal foil. This apparatus thus allows a selected area to be repeatedly observed following successive accumulations of fatigue damage without removing the specimen from the electron microscope.

Consideration of sorption of water vapour during air flow through a hygroscopic porous bed leads to the idea of a `temperature of adiabatic drying', the converse of the better-known `temperature of adiabatic saturation'. The temperature rise of the air is a measure of absolute humidity, and is so used in an experimental hygrometer.

An apparatus combining internal circulation with a temperature gradient technique has been used for growing water soluble crystals. Its advantages are the small volume and growth control which can be achieved without the usual defects of circulatory techniques.

A method of aligning x-ray diffractometers using a light source mounted on the detector arm is described. It enables the axis of the receiving slit to be set parallel to that of the divergence slit and the `angle of acceptance' to be adjusted.

A simple evaporator for use in a JEM6A electron microscope has been made by slightly modifying an existing specimen heating device. Since the maximum permissible operating temperature is about 1000°C the device may be used to evaporate silver at a fairly rapid rate.

A plate valve has been designed to connect two sections of a tube which is filled with gas at pressures above or below atmospheric. The bore of the tube is clear when the valve is open but maintains pressure or vacuum seals in the closed position.

The valve is mounted as a flange between the two sections of the tube and operated by the rotation of an outer ring enclosing the flange.

A simple method for sealing suitable metal rods into a glass envelope is described. This technique is especially recommended for multiple seals, used for experimental purposes.

A low cost, easily constructed flame ionization detector cell for gas chromatography has been designed and tested. The details of construction are given. The detector output measured with propylene was 3μA mg^-1 sec.

A method is described of preparing hot wires which enables the wires to be discarded after a short period of use. A detailed description is given of how the hot wire is fastened to the supporting needles.

A method was required for the rapid measurement of the parallelism of the pole pieces of an electromagnet while the field was on. A pneumatic gauging device, having variable sensitivity enabling measurement to better than ±20 μin was found to be suitable. Any tilting due to asymmetric bending of the yoke is easily detected.