Table of contents

The principal operating characteristics of heat pipes are briefly outlined and factors governing their selection, design and manufacture are discussed. Ways in which heat pipes have been used to improve the performance of a wide range of scientific instruments are then reviewed. Applications cited cover conditions involving the controlled transfer of heat at temperatures from 50 to 2000K and with powers ranging from a few watts to several kilowatts.

Presents the results of a survey of the members of the Crystallography Group of the Institute of Physics concerning the conditions under which they use X-ray tubes, in order to determine how to get the best results from various makes of apparatus.

A simple and inexpensive system has been developed for the acquisition and the processing of kinetic data obtained by stopped-flow spectrometry. The main components of the system consist of an analogue-to-digital converter, a memory and a series of appropriate control circuits. The memorized data are transmitted to a programmable calculator point by point using an interface, and the rate constant is calculated by a least squares program.

Subnanosecond resolution is possible in time interval measurement using the Vernier principle. Central to the technique are the accuracy and stability of the phase detection system. It is shown that a high-speed comparator can be used to achieve a predictable resolution better than 25 ps RMS.

When a fast circuit breaker operates in an inductive circuit it is necessary to limit the voltage between the opening contacts to less than 50 V to permit extinction of the arc. Fusible shunts of copper foil carrying a current density of 20 kA mm^-2 for 200 mu s allow the contacts to open sufficiently to withstand a potential of 4 kV, when the shunt melts. The foil must be clamped solidly between woven asbestos and pasteboard sheets to prevent an arc from continuing in the residue of molten copper. When packed in this manner the energy used in the destruction of the shunts is insufficient to vaporize more than a very small fraction of the copper.

A digital trigger delay unit is described which automates coherent variable-path-length measurements of ultrasonic velocity and attenuation. The sampling gate of a boxcar integrator is delayed by the device in such a way that it always opens in the same time slot of a progressively delayed received signal. The device has been used in the measurement of velocity and attenuation in gases.

A simple gas-supply line is described which allows a high voltage to be maintained across its ends at gas pressures in the gas line at which electrical breakdown would normally occur. It consists of a series of insulated electrically conducting tubes across which resistors are connected in a similar manner to the dynode resistor chain of a photomultiplier. In the present application a voltage of 2.5 kV is maintained across the ends of the gas line, but this may readily be increased.

A simple voltage scanning system for sector field mass spectrometers is described. The ion injection voltage is derived from a potential divider comprising a fixed resistor in series with a linear potentiometer, the shaft of which is rotated at a constant rate by means of a synchronous motor. It is shown that this arrangement will provide an exactly linear mass scan.

A new design of specimen cup for a transmission electron microscope (TEM) equipped with side entry goniometer and a double tilt specimen stage is described. The new cup is a direct substitute for that originally fitted, and when used in the microscope, which is equipped with an energy dispersive X-ray analysis system, results in a substantial reduction in the intensity of 'system peaks'.

An instrument suitable for measuring the distortion of piezoelectric transducers has been developed. The device has been used to measure the distortion in cylindrical piezoelectric elements of the type used for modulating the mirror of a frequency-stabilized gas laser.

A pulse programmer is described which generates a wide range of pulse sequences for use with nuclear resonance equipment. The use of CMOS integrated circuits makes the unit extremely small and cheap and allows the incorporation of a very simple power supply.

An automatic microtone has been designed for cutting 400 mu m snippets of wool and other fibres very uniformly and with square ends.

A psychrometer for measuring plant and soil water potentials is described. It automatically reads and prints out in digital form the output from 100 chambers fitted with different wet and dry ring thermocouples. The first channel in each scan is a reference channel to check the measuring system. Unwanted channels may be shorted by inserting pins in a matrix board and for other channels the output can be adjusted to read directly in water potential units. The instrument scans at 3 s per channel with a standard deviation of 5.58 J kg^-1 for any single observation. It is programmable and can automatically repeat up to a maximum of 11 scans at preselected time intervals of up to 60 min between scans, and then follow preselected final state instructions to revert to 'Ready', 'Standby', or 'Off'. A clock switches the instrument of 'Standby' early in the morning to enable the amplifier to stabilize before the working day begins.

A new precession camera furnace has been designed and tested. No temperature gradient exists within the crystal because of the technique of indirect heating used. A temperature regulator has also been designed which regulates the temperature with an accuracy of +or-0.5 degrees C. This enables structures of the modifications which exist in a very small range of temperature to be studied.

Describes a modification to commercial glass-PTFE stop cocks to permit their use at elevated temperatures and pressures.

A simple formula is given for the calculation of junction temperature from the measured EMF of a type 'T' (copper-constantan) thermocouple. The formula is accurate to better than 0.1 degrees over the range -200 degrees to +400 degrees C, and requires only eight arithmetic operations for its evaluation.

The Mossbauer absorption spectrum of a single (not multilayer) nickel ferrite film of 0.5 mu m thickness has been obtained with a commercially available high counting rate Mossbauer spectrometer. This is not possible with a standard where absorbers, in multilayer or sandwich form, are needed.

A description is given of the design and operation of an apparatus for testing the resistance of materials to corrosion in a variety of aqueous environments at temperatures up to 250 degrees C. Particular features include the ability to allow tests in static solutions of very corrosive substances and to refresh or change less corrosive solutions during the test to keep contamination to a minimum.

A new integrated semiconductor transducer suitable for colour distinction is proposed. This device consists of a SnO₂-Si heterojunction covered with a colour filter which is highly photosensitive and has a fast response time. The transparent SnO₂ thin film on a Si wafer is separated into three photodiode regions by photoetching methods. The device is covered with a filter composed of three primary colours (red, green and blue). Thus colours in a section of the Maxwell triangle can be distinguished by one photodiode or a combination of the three photodiodes. This device for colour distinction can be made very compact by means of semiconductor integration techniques.

The paper describes an apparatus for the measurement of the thermal conductivity of non-conducting liquids under their saturation vapour pressure. The instrument, which is based upon the transient hot wire principle, has been designed so that the measuring element conforms as closely as possible to an infinite line source of heat in an infinite fluid. Under these conditions the thermal conductivity of the liquid can be determined from the slope of a plot of the temperature rise of the heating element against the logarithm of time. The measurement system has been arranged so as to provide as many as 60 points on this plot for any particular thermodynamic state of the fluid under investigation. The reproducibility of the instrument is of the order of 0.03% and the precision of the measurements is estimated as +or-0.1%. Owing to a lack of a suitable theory for the effects of radiative heat transfer, the accuracy of the thermal conductivity values cannot be defined unequivocally, but a reasoned upper bound is +or-0.3%. Preliminary results are presented for n-heptane at three temperatures in the range 20 to 30 degrees C.

The composite wall hollow cathode is a new type of source, set up for studies of the emission spectra due to electronic transitions in diatomic molecules. This lamp is characterised by the wide range of emitted spectra, its stability, its capacity to identify new molecules easily and to emit at low or very low rotational temperature. It enables an easy systematic search to be made for spectra which have not yet been observed. Moreover, the possibility of emission at different temperatures-and in particular at very low temperature-facilitates rotational studies. The best conditions of utilisation are described. The lamp is able to run for several months at an intensity of about 50 mA and, for a given low temperature of the discharge gases, it is approximately one hundred times more intense than a traditional hollow cathode lamp.

An apparatus is presented which compensates automatically for the ohmic voltage drop occurring in electrochemical potentiostatic measurements, between the working electrode surface and the tip of the capillary connected to the reference electrode. The apparatus measures the potential during very short interruptions of the current. It has an input impedance of 10 T Omega and can be connected to any potentiostat or current source and adapted to the system under study. The instrument operates over large ranges of current and potential, regardless of the polarity.

A new constant temperature thermistor anemometer for very low gas velocities is described. The principle of a constant temperature method and the operation of the instrument are outlined. With the electronic equipment used, the temperature of the probe can be fixed independently of both velocity and temperature of the gas flow. Good stabilisation of the resistance and hence of the temperature gives a short response time which is compatible with measurements of atmospheric turbulence. The nonlinear term in the expression for the thermistor's temperature coefficient can therefore be neglected. The experimental calibration curves agree well with King's linear law.

The sensitivity of constant temperature hot wire anemometers to velocity perturbations in an air flow was measured by the traditional static calibration technique as well as by the recently revived dynamic method in which the wire is shaken in a steady flow. Contrary to previously published findings, the two methods gave calibration constants which agreed to within an experimental standard error of 2% in the velocity range of 3-32 m s^-1. A new signal processing technique was used for the dynamic calibration method which gave better accuracy in the presence of electronic noise and wind tunnel turbulence than the RMS method used to date.

In amorphous materials, the lack of long-range order as well as a relatively poor short-range order lead to a change in hyperfine interactions from nucleus to nucleus and the Mossbauer spectra have to be analysed in terms of a continuous distribution of characteristic parameters. A method is being proposed for calculation of simultaneous hyperfine magnetic fields and electric field gradient distributions.

A simple system is described in which a superconductive coil is used to produce an oscillating magnetic field of amplitude 0.04 T for field modulation of a steady background of up to 8 T. The performance of the AC modulating coil at frequencies below 16 Hz is presented and a quantitative explanation of its behaviour is given. Possible improvements to the design are suggested to extend the modulation technique to higher ambient fields.

The absorptivity of highly reflecting surfaces can be measured with relatively high sensitivity by using a nonresonant cavity made of the material of interest. The operation of such a cavity has been studied both theoretically and by computer simulation in order to establish the limits of applicability of the technique, and the results of this investigation are discussed. A system has been developed which allows the comparison of the absorptivity of a dilute alloy with that in the pure host metal and some preliminary results on CuNi are described.

The application of oil film interferometry to the measurement of skin friction in air flow was described in an earlier paper by Tanner and Blows (see ibid., vol.9, no.4, p.194 (1976)). This work is extended in various ways. These include use of oil droplets as an alternative or in addition to continuous films, particularly for exploration of three-dimensional flows. The use of accidentally or deliberately introduced disturbances as streamline markers is described. The use of the characteristics method to follow transient changes of oil film profile is demonstrated. Many checks on the consistency of the methods and comparisons with theory are given. The results suggest that the methods can give a wealth of information concerning surface flows which would otherwise be difficult, if not impossible, to achieve.

The thermo-EMFs of tin-lead alloys in the composition range of 0-100% have been measured against copper for temperature differences of up to 100 degrees C. It was found that there is a dip in the thermo-EMF-composition relationship at 18% tin. The thermo-EMF for SnPb4O alloys used for electronic assembly is 145 mu V at 50 degrees C temperature difference between the hot and cold junctions.

Automatic circuitry for monitoring an RF SQUID sensor is described. The system performs several trimming procedures and provides an output in terms of the flux quantum. Circuit diagrams and adjustment procedures are discussed.

A closed type of suspended level glass capillary viscometer is described. It has several advantages, one being that there is no need to suck up the test liquid which, since it is completely enclosed in the viscometer, can be volatile, unstable or reactive.

The rotational diffusion coefficients of a fluorescent molecule can be determined by measuring the time-dependent anisotropy r(t). The errors introduced in such measurements by misalignments in the setup are discussed. Since the single-photon sampling technique normally used is nonlinear, the necessary normalisation of the intensities I/sub /// and I_{perpendicular to} is considerably complicated. A correct normalisation procedure is described and the sensitivity of the method is shown in a measurement of micellar rotation.

A simple hot wire liquid level sensor suitable for accurate detection of liquid levels is described. The sensor is characterised by a fast temporal response of typically 20 ms for slow immersion in organic liquids and 5 ms for immersion in water. Temporal response improves as the immersion speed is increased. The sensor is inexpensive, compact, of simple construction and is suitable as a level detector for a wide variety of liquids over an extensive temperature range. A smooth liquid surface may be located to within an accuracy of better than 100 mu m. Application of a combination of two level sensors to the absolute measurement of volumetric flow rates of free flowing liquids is also described.

The effect of pressure at low temperature (166.8K) upon the R₁ and R₂ lines of ruby has been investigated for the first time to establish a calibration for use in high-pressure/low-temperature work. A reinvestigation of the behaviour of R₁ and R₂ at ambient temperatures and at pressures up to ca 70 kbar supports previous work on the calibration under hydrostatic conditions but shows that in a 4:1 methanol:ethanol mixture conditions become nonhydrostatic at lower pressures (ca 50 kbar) than claimed (ca 100 kbar). The importance of monitoring both R₁ and R₂ is emphasised as their relative shifts are sensitive indicators of the presence, and approximate magnitude, of non-hydrostatic stress components. It is shown that although changes in half-bandwidths are also associated with development of shear stress, their use in estimating gradients is extremely hazardous and can indicate values greatly in excess of the known shear strength of the material.

A guarded flat-plate thermal conductivity apparatus has been designed for use with gases and liquids in the temperature range from 3 to 50K and for pressures up to 4 MPa. Temperature measurement is by means of five germanium resistance thermometers which are not in contact with the test fluid. The geometrical cell constant is obtained from an electrical capacitance determination. Measurements with the apparatus of the thermal conductivity of helium 4 at approximately 10 kPa pressure over the temperature range from 3.3 to 20K are presented.

An improved laser-driven Michelson interferometer for calibrating and checking the linearity of Mossbauer drive systems is discussed. The design avoids velocity errors so that the calibrator may be used at velocities down to the lowest normally used in Mossbauer spectroscopy. The effect of the necessary hysteresis in the fringe-counting electronics is analysed and the use of the calibrator is demonstrated by examining the linearity of various drive systems. It is shown that recoil of the drive vibrator is the major problem in obtaining a linear velocity scale.

Combines the theoretical analysis and practical design of an electrostatic transducer capable of detecting, in metal specimens, surface (Rayleigh) waves with displacement amplitudes less than 10^-8 cm. This form of transducer is offered as an alternative to electromagnetic acoustic transducers as a means of receiving ultrasonic Lamb and surface waves in nondestructive test applications. It also provides a means of calibrating the amplitudes of ultrasonic surface waves generated by any means.

A gas-filled X-ray tube resembling that of Solomon and Baun (1969) has been constructed and used successfully as a linear X-ray source in a grating spectrometer RSM-500 in an ultrasoft X-ray region (Lukirskii 1961). The tube does not suffer from the carbon contamination and consequent reduction of intensity that are characteristic of hot cathode tubes.