Table of contents

A comparison is made of vacuum electronics and the new electronics using crystalline solids. The very stringent requirements as regards chemical purity and structural perfection of the crystals are discussed. Some experiments which have been made possible through the availability of such high purity crystals are described, including some recent work on semiconductors. A brief account of atomic amplifiers using paramagnetic crystals is also given. The effect of these new developments in the application of the physics of solids on the training of electronic engineers is discussed.

The energy of the ion beam from the accelerator is measured and stabilized with an accuracy of better than 0.1%. The main energy measuring device is an electrostatic analyser which is energized from a stabilized power supply whose voltage is referred to standard cells. A generating voltmeter is used as an auxiliary measuring device, and a method is described by which a very fast response may be obtained from this instrument. An electron beam loading the generator is used as a fast acting control device, while long term variations are taken up by automatic control of the spray current.

A description is given of the construction and performance characteristics of an instrument which is capable of measuring flow speeds in water "at a point" over a range of 1 to 14 ft/s. The accuracy at 1 ft/s is approximately 1½% and improves rapidly with increasing speed. The Leon tube is of robust and compact construction and is, in effect, a combination of a differential pressure tube and a differential liquid manometer. The pressure factor of the tube, which is a function of Reynolds number, is most readily determined in a wind tunnel. The instrument has proved to be particularly suitable for the performance of velocity traverses in open channels.

The most efficient method of adjusting an optical system to satisfy prescribed Gaussian conditions is given. Additional formulae relate such adjustments to errors present in the components of the system.

The paper describes the properties of InSb detectors, at room temperature, using the photoconductive process, and experimental work on sensitive p-n junction detectors, cooled to 90° K, used as photo-voltaic cells.

The difficulty of measuring the small departures from linearity in the extension of steel specimens subjected to cyclic tensile loading was overcome in this case by comparing the extension of the specimen with that of a member of which the stress-strain curve is, by comparison with the specimen, linear. The scatter of the results obtained with this apparatus indicates that the accuracy of observation of a single strain-hysteresis loop is 4%. The effect was investigated of increasing the direct load while keeping the amplitude of alternating load constant. Stresses were confined to the normal working range.

The drawbacks of types of instrument in common use are reviewed. It is shown that primary aberration theory predicts quite accurately the errors introduced even by simple collimators with large aberration. The advantages of using a collimating lens based on a multiple-meniscus design are indicated, and the performances of several lens-systems are compared.

The usual saw-tooth time-base of an oscilloscope is replaced by one in which the spot moves with acceleration. Pulses from a radiation detector are displayed as bright dots which occur mainly on the side of the screen where the spot is moving slowly. Integration by time exposure with stationary film gives a record in which a constant-density line is a graph of pulse frequency against pulse height. Visual observation of the spectrum is possible with abundant pulses. The two simple circuits used employ only four tubes between them.

The construction and calibration of a capsule-type pressure gauge for the range 0-20 mm of mercury is described. Incorporating both mechanical and optical amplification of the capsule movement, the gauge is direct-reading and independent of the nature of the gas under pressure. Sources of error in construction and calibration are examined and an accuracy of better than 1% at 1 mm of mercury and 0.1% at 20 mm of mercury is shown to be obtained.

Details are given for the design and construction of an electrical resistance analogue having a graded mesh. The network is economical to build and, since it consists of eight separate units, it can be assembled in a variety of ways. Thus, for any particular problem in fluid mechanics or elasticity, a suitable and efficient analogue is readily available and it has been successfully used to solve a wide range of problems in these fields.

Apparatus is described for transferring increments of gas at low pressures from one section to another of a vacuum system. The measurement of the volume of the gas and the operation of transferring it involve its coming into contact with glass and mercury only.

The construction and performance characteristics of a low air-speed indicator, which can be used as standard of comparison for the routine calibration of anemometers in a wind tunnel, are described. The apparatus is essentially a very sensitive drag balance in which the forces acting on a disk are utilized to determine the air speeds. The effective range is from 0.2 to 16 ft/s, and the indicator conforms to all the requirements that may be imposed on a standard of its type.

It is shown that steady acceleration is possible in the cyclotron, for ions which take an even number of radio-frequency cycles for one revolution, if the centre of revolution is to one side of the dee gap. The acceleration of HD⁺ ions, taking two radio-frequency cycles to complete one revolution, has been observed and confirmed by several methods. The contribution of this process to the production and acceleration of multiply charged heavy ions is discussed.

Corrections to 1957 J. Sci. Instrum.34 257.