Table of contents

The performance characteristics of modern vacuum pumps are critically discussed, providing criteria which are useful in the selection of pumps for particular applications. The review includes pumps of the following types: sputter-ion, electrostatic-ion, sublimation, getter, turbomolecular and diffusion. The application of roughing pumps for each of these groups is also discussed.

Reflection of gas radiation by a ribbon filament lamp used as a comparison source can cause errors in the determination of gas temperatures by Kurlbaum's method and by the sodium D-line reversal method, unless the full radiation flux equation is employed. The full equation is presented here and the errors given by the existing equation are considered.

The design of a simple cell for conductivity studies of aqueous solutions to 250 degrees C and 2000 bar is described.

The self-triggering action of the TVG under DC conditions using the same power source as the main circuit is described. Because of the low impedance of the power source compared with the thyratron pulse generator, the TVG can be triggered with voltages as low as 85 V. It is found that circuit conditions influence the minimum stable arc currents that can be sustained.

A simple unit is described which can easily be adapted to various instruments in which a scanning function is involved. For example, in mass spectrometry, where only certain peaks or mass ranges are usually of interest, the unit can be used to skip the uninteresting parts of the spectrum. In this way a high resolution can be combined with a high throughput. This is of particular interest in cases where a restricted number of species has to be evaluated over a long period.

Experiments are described which show that a monobath can be used for rapid in situ processing in a liquid gate for real-time holographic interferometry. This also permits utilization of a very simple solution handling system. Changes in emulsion thickness are reduced to an acceptable level and problems of matching refractive indices are eliminated by exposing and viewing the holograms in water. Excellent null patterns are obtained and real-time holographic interferometry can be carried out over long periods of time.

The design and use of an unusual type of rotary feedthrough for ultrahigh vacuum systems is described.

A small surface plate calorimeter, about 8 mm*12 mm*0.2 mm thick, is described for measuring the steady state convection and radiation heat transfer from the surface of a heated body in air. The calorimeter, which may be attached to the surface of the body with double-sided adhesive tape, has been tested on heated cylinders in free and forced convection.

The design and operation is described of an instrument for the manipulation of small crystals which require, for stability, the presence of a saturated atmosphere. The instrument should be of considerable use to X-ray crystallographers handling very small crystals of materials such as proteins.

The principal design of a charging unit for capacitor banks is given. The charging voltage can be adjusted in a wide range. After charging the capacitor bank its value is held constant. The design of an example with a maximum charging current of 2.8 A, with the charging voltage in the range 45 to 250 V, is described.

Describes a device which employs a single rotary feedthrough to produce, in the vacuum system, a combined linear and rotary motion for machining purposes. It can be mounted directly on to the experimental chamber with the cutting tool protruding into the target area. A variable speed motor drives the rotary feedthrough thus allowing smooth advance on the target and variable pressure of the cutting tool. No sample preparation chamber is necessary, hence vacuum locks and differential pumping techniques are avoided.

A versatile hot torsion testing machine has been developed to simulate deformation schedules encountered in practical hot working operations such as rolling or forging. Programmed deformation for strain rates covering seven orders of magnitude can be carried out. Two particular features of the machine are a high speed clutch-brake system and a digital programmer. The clutch is capable of accelerating the sample from 0 to 3000 rev min^-1 in 2 ms. The programmer is capable of up to 60 steps, 10 output functions and time ranges from 1 ms to 10⁵ s.

To meet the rigorous requirements of a polarized neutron diffraction experiment using a dynamically polarized proton target, a superconducting magnet has been constructed with magnetic field homogeneity better than 1 part in 10⁴ over a 1 cm³ sample volume. It has also the essential characteristics of wide angular access to the sample, and, to avoid depolarization of the neutron spin, no field nodes in the neutron beam line. To achieve these specifications an asymmetric split-pair coil configuration, coaxial with a smaller pair of fourth order correction coils, is used.

The design of a simple self-balancing AC resistance bridge with digital readout is discussed. The instrument operates with an extremely small power dissipation in the unknown, and is particularly suitable for use with carbon resistance thermometers at low temperatures. An accuracy exceeding 0.5% is obtained over the range 20 Omega to 2M Omega .

The construction of an ellipsoid voltmeter for the measurement of high voltages using an ellipsoid with a ratio of axes of approximately 2 to 1 is described. The voltmeter was operated to a maximum voltage gradient of 5.1 kV cm^-1, and an absolute accuracy of better than 0.5% for voltage measurement has been achieved.

In certain battery applications, e.g. energizing tiny electrostatic oscillators useful for timepieces, the power needed is very modest (about 0.5-1.5 mu W) but the output voltage must be high (500-1500 V) and a long lifetime is desirable. These requirements can be met by an isotopic battery, based on the collection of charged particles emitted from a tritium source. The report describes the theory and present state of development of such a battery, mechanically designed to fit into the case of a wristwatch.

A portable dust monitor capable of measuring the concentration of respirable dust continuously for a period of 8 h has been designed and constructed. The monitor utilizes the principle of light scattering by individual particles from the cavity beam of a gas laser. The instrument provides instantaneous meter readout and continuous recording.

A slotted disc velocity selector is described that can be used to transmit a number of different velocities in the range 102-688 m s^-1 with the selector rotating at 6000 rev min^-1. Corresponding velocity resolutions lie in the range 1.8-12.2%. The selector is driven by a three-phase synchronous hysteresis motor operated by passing direct current through each motor phase in turn for 120 degrees phase duration. Control is exercised by means of logic circuitry so that speeds up to the peak value of the motor, 12000 rev min^-1, were readily obtainable with a stability of less than +or-0.1%.

A high spectral resolution, photoelectric spectrometer is described which employs a Fabry-Perot interferometer in tandem with an echelle grating monochromator. Spectral recording is achieved by simultaneous mechanical scanning of the interferometer and the grating premonochromator. The spectrometer is intended for use in a programme of astronomical spectroscopy in the middle ultraviolet. Design considerations and some details of the performance of a prototype instrument in the ultraviolet are presented.

A circuit to perform time-resolved Langmuir probe measurements in low-pressure gas discharges is described. The condition to be fulfilled is that the plasma variations must be repetitive with a constant frequency of at least about 100 Hz. The second derivative is approximated by the second differences of the successive measuring points of the current-voltage probe characteristic. These second differences are obtained directly with a time resolution of 1 mu s.

A technique using a composite bar is described which enables measurements to be carried out at low kilohertz frequencies in small alkali halide crystals. The technique allows measurements to be made over a range of frequencies on a small sample of an alkali halide and thus the acoustic relaxation process associated with the divalent cation-vacancy dipole can be examined.

A portable device which may be used for transferring evaporated thin films between a high vacuum evaporator and an optical bench assembly is described. The device enables the samples to be transferred under a vacuum of better than 10 mu torr and at liquid nitrogen temperature.

A simple electronic divider is presented and its application in the case of a differential reflectometer is discussed. The circuit has the advantage that it can be cascaded for better accuracy and is more convenient to use than alternative techniques.

One of the main difficulties in turbulence measurement using a yawed hot wire is the determination of the probe sensitivity to perturbations in the velocity components. Direct differentiation of the anemometer output for independent changes in two velocity components tends to be inaccurate because it makes exceptional demands on the skill of the operator and performance of the calibration equipment. A second approach is to calibrate for changes in one component only and deduce the transverse sensitivity using the measured wire inclination and an assumed law for deviations from the cosine law of cooling. However, the second method is very sensitive to errors in measurement of wire angle and formation of the cooling law. A new procedure has been devised which combines the advantages of both methods mentioned above. The method is insensitive to errors in measurement of wire angle, does not require explicit differentiation with respect to the transverse component of velocity and does not depend on the choice of a particular cooling law. The procedure is deduced via a Taylor series expansion in the deviation from a cosine law of cooling. It also allows direct use of published data for deviations from the cosine law, if the wire inclination can be specified accurately.

For abstract of pt. II, see abstr. A59650 at 1972. The RF drift-off and harmonic peaks caused by a nonuniform RF field are experimentally verified. This RF field, combined with a modified DC field, gives a great improvement in the resolution. Some design considerations for a long omegatron are given.

A zero-method torsion effusion device with a bifilar suspension is described. The apparatus overcomes the drawbacks of a unifilar suspicion as it allows for direct temperature measurement of the sample. In addition, the exerted effusion torque is compensated electromagnetically, thus making the device independent of the torsion constant. The pressure range is from 10^-1 to 3*10^-6 Torr. Measurements on acridine are given as an example.

Compression and tension devices for use in the assessment and comparison of force standard machines are described. A higher sensitivity than with normal proving devices is achieved, permitting a greater precision in the measurement of the forces being applied to the device. In addition, the device can detect any nonaxial application of force and hence a control of nonaxiality of forces can be exercised leading to the reduction of frictional forces to a minimum in certain types of force standard machines.

The apparatus described is intended for measurements of tunnel junctions. By using voltage-controlled current feedback the sample bias (AC and DC) is kept independent of sample resistance. The separation of the current feedback into a DC channel and a narrow bandwidth AC channel (modulation frequency) makes calibration easy. By further separating the AC feedback output into its in-phase and out-of-phase components the parallel capacity of the sample can be determined. The use of potential sensing lines allows measurement on four-probe samples.

A simple and inexpensive neutron guide tube is described. Curves for the easy determination of the characteristic wavelength, spectral maximum, and neutron current distribution at the exit of the tube are presented. The method of mounting and alignment of the single tube and results for two different guide tubes in comparison with calculations are reported.

An X-ray fluorescence unit has been designed for the microanalysis of thin biological specimens. Excitation is by means of a microfocus X-ray tube with transmission anode, and the X-ray spectroscopy is based on a Si(Li) detector. Tests show that the unit in its present form can measure amounts of potassium down to approximately 10 pg and potassium mass fractions down to approximately 30 ppm. Quantitative analysis is based on a normalization of the fluorescence signal against the measured intensity of scattered radiation.

The theory of a beam modulation technique, hitherto not used in time-of-flight mass spectrometry, is presented. Salient features of this technique are: firstly, resolution is independent of mass; secondly, resolution is independent of the location where the ions are initially formed; and thirdly, resolution is proportional to the square of the length of the drift space.

For abstract of original paper see abstr. A5543 of 1973.

Reports the measurements on the time resolution of an Ortec coaxial Ge(Li) detector of 7 mm depletion depth and 6 cm² effective area in the energy range 32-1830 keV.