Table of contents

The application of semiconductor devices to the detection and analysis of gamma ray, X-ray and nuclear radiations is outlined. After a brief discussion on semiconductor detector principles, including mode of operation, choice of material and energy resolution various types of semiconductor detector are described. The uses of semiconductor devices in the fields of nuclear particle counting and spectrometry, gamma spectrometry, space physics, medical physics and energy dispersive X-ray spectrometry are discussed. Despite the great importance of processing the detected signal, only brief mention is made of the electronic techniques used, emphasis being on the detecting devices themselves.

The performance of a cylindrical hot wire gauge head operating by thermal conduction at low pressures and natural thermal convection at high pressures was evaluated. The advantage of wall temperature sensing used in conjunction with a constant temperature difference control unit is discussed and calibration in air up to atmospheric pressure is reported.

A capillary viscometer has been developed which is applicable to volatile liquids or solutions over a wide temperature range. The instrument is particularly useful for toxic and corrosive substances.

A coaxial capacitance voltage divider with a ratio of 110 and a rise time much less than 2.5 ns was developed for use with a transmission line pulse generator capable of producing 100 kV rectangular pulses of 2 mu s duration. The low voltage arm of the divider is a 3 cm long tube of titania (TiO₂) turned out from a cylindrical compact. The compact was made by first pressing titania powder using a suitable binder and then sintering at controlled temperatures. The tube was slipped over the terminating end of the pulse-forming cable to form the divider with the cable capacitance.

An electrical device allowing the sample to be moved under observation is described. The motion, at variable speed and in any direction of the plane of observation, is obtained from a single shaft. With this device disengaged, the manual displacement of the sample is still possible. This apparatus can be mounted on most of the usual types of microscopes.

A simple inexpensive device is described, which tensions and spools the punched paper tape emerging from teleprinters. It is effective in overcoming the 'bunching' of the punched tape which can occur immediately before the tape punching mechanism.

An apparatus has been developed for the growth of large single crystals from minimum quantities of solvent. The technique has been used to grow crystals of potassium dihydrogen orthophosphate and potassium dideuterium orthophosphate, the latter from D₂O.

A sampling valve for gases or liquids is described, which is capable of operating at high sample pressures (up to 74 kgf cm^-2) or at high temperatures (up to 300 degrees C). For the high pressure operation a Kel F-Teflon-Molykote composite sealing material has been developed. Typical operating conditions are 62 degrees C and 35 kgf cm^-2. When provided with sealings of commercially available polyimide the same valve can be used at temperatures as high as 300 degrees C and pressures of a few atmospheres. The valve is particularly suitable for studies in gas kinetics, since very small vapour or liquid samples can be injected directly from a reaction system into the gas chromatographic column.

Describes a simple triggered vacuum gap developed for initiating electric arcs in vacuum which uses the property that the voltage required to breakdown a gap in vacuum in the presence of a solid insulating material is considerably less than the voltage required in the absence of such material. In this triggered vacuum gap a solid insulating material is used in the angular space between the main cathode and the concentric trigger electrode forming the auxiliary gap. Different materials like epoxy resin, Teflon (PTFE) and mica have been used. The trigger voltage was found to vary in the range 560-1840 V. The results with epoxy and Teflon were unsatisfactory because the trigger voltages showed wide scatter and the auxiliary gap was soon bridged by metal particles eroded from the electrodes. Though the trigger voltages required with mica were relatively high, consistent triggering could be obtained for a large number of trials before the auxiliary gap was bridged. This was probably due to better thermal stability of mica as compared with either epoxy or Teflon.

A simple apparatus is described for electropolishing thin foils at -50 degrees C. Cooling is effected by a closed pumping system, which transfers heat from the solution in the electropolishing cell to a large reservoir of solid CO₂ and ethanol maintained at about -70 degrees C.

Describes the structure of an isolated target designed to eliminate contamination of the sputtered films by effective cooling. It consists of a copper base separated from the target by a plate of alucer with efficient sealing at the interfaces.

A system using Hengstler predetermining impulse counters to control a step scanning X ray powder diffractometer is described. The control system advances the goniometer rapidly to the preselected angular ranges through which detailed step scans are required. Preset time or preset count step scans may be used with typewriter or punch output. The system for scanning four angular ranges was built for less than Pounds 100.

A 10 m, thermally stabilized steel measuring base has been constructed in a deep underground laboratory. Length is maintained constant to at least 2 parts in 10⁹ per hour by an on-off temperature control system. Results are compared with those obtained from a similar base built in 1968, which was situated in a surface laboratory.

A low-temperature calorimetric technique for heat capacity measurement of small samples is described. The sample is connected by thermal resistance to a thermal sink at a chosen temperature. The precooling of the sample to this starting temperature is simple and fast. The sample temperature rises exponentially in time after electrical heating power is applied to it maintaining the sample in near thermal equilibrium with its surroundings. An analogous electrical circuit of such microcalorimeter is introduced and analysed to establish conditions for its realization and to determine the possibilities for the interpretation of experimental temperature-time curves. More than one sample can be maintained in the cryostat. It enables comparison to be made between the results obtained with an unknown sample and those obtained with standard samples of known heat capacities used as references.

Describes a series of experiments designed to investigate the factors which limit the maximum resolution obtainable with a conventional quadrupole mass spectrometer under normal operating conditions. Included in the investigation were the effects of imperfections in mechanical construction and electrical supplies and also operation with contaminated electrode surfaces. In normal operation and with reasonable care taken in the mechanical construction and assembly, the finite length of the quadrupole rods, in this case 150 mm, was the principle factor setting an upper limit to the resolution. All the results suggested that the ions did not spend a sufficient time in the quadrupole to reach an equilibrium oscillation in the transverse AC field. Under all operating conditions resolution was found to be dependent, to a first approximation, on the number of cycles of AC field N experienced by the ions. The dependence of maximum resolution R_m on N was found to follow the simple empirical relationship, R_m=KN^1.7. This formula applied for both low and high energy ions (2-32 eV) and for the mass range H₂⁺ to Xe⁺.

Two identical, astable multivibrators synchronized together form a temperature stabilized, fairly linear bridge, which may be used for balanced/unbalanced measurement of the R or C parameters of resistors, capacitors or transducers of nonelectric quantities. Theoretical and experimental analyses are given. The device may also serve as a new type of DC electronic potentiometer. At higher frequencies sensitive measurement may be carried out by beating fundamentals or higher harmonics, which may make it also useful as a warning device. It can be versatile: here it is used for temperature measurement by a thermocouple.

Utilization of a general purpose computer in controlling pulses and data collection in NMR Fourier spectroscopy is described. Coherent addition of free induction decay signals can be achieved for analogue-to- digital conversion rates up to 20 kHz with an IBM 1800 computer. Stochastic excitation and signal detection are time-shared in order to suppress leakage. The benefits of this procedure, compared with the pulse excitation method, are low peak power requirements and the fact that resolution and sensitivity can be set independently. However, contrary to the pulse experiment, care must be taken with the receiver system in commercially available high-resolution NMR spectrometers. For high conversion rates, ringing and saturation of the narrow band detector might necessitate the exchange for a broad band amplifier.

A stable, sensitive in-reactor creep machine is described suitable for operation in the temperature range 200-800 degrees C and for nuclear heating rates up to 3 W g^-1 in steel.

Three methods, two optical and one electromechanical, have been employed for determining film thickness by measuring the step height at the edge of the film. The optical techniques were multiple-beam Fizeau interferometry and photoelectric shearing interferometry while the RPI Talystep, a stylus measuring instrument, provided the third method. The three techniques have the common feature of possessing extremely high sensitivity and their merits and disadvantages are discussed. A comparison of measurements on magnesium fluoride, aluminium and gold films with thicknesses ranging between 100 and 2000 AA is presented and shows that results from the three methods were generally in excellent agreement, the overall spread of values rarely exceeding 10 AA.

The observatory system under test at the three Uk observatories which are operated by the Institute of Geological Sciences is described. It uses backing-off fields to allow component measurement to be made by rubidium magnetometer sensing heads. The current test schedule includes comparative evaluation of the 'skew D' and 'direct D' methods of obtaining the components of the horizontal field variations as well as examination of backing-off field stability and the development of software for both routine processing of data and filing of special events for research programmes. The frequencies of the component Rb sensors are counted synchronously and recorded serially together with appropriate time information on IBM/INDUSTRY compatible incremental magnetic tape. The magnetic tapes are machine readable without intermediate processing. The system is capable of a resolution of 0-005 gamma and has a bandwidth from 5 Hz to DC, the effective long term resolution being limited by the electrical and mechanical stability of the backing-off fields.

Several open-channel photomultipliers have been flown in an instrument on the satellite OSO-6, and their detection sensitivities two sources (thermocouple error and thermocouple location.

The temperature of an experiment performed in a Tuttle hydrothermal pressure vessel may be subject to error from two sources (thermocouple error and thermocouple location error) and uncertainties from five sources (uncertainties in the previous two errors, temperature fluctuations, temperature gradients and pressure effects). The evaluation of each of these effects is discussed. The narrowest limits of accuracy which may be achieved with this apparatus in routine use is +or-3 degrees C. Two definitions in which the limits of accuracy of a measured temperature are taken as the sums of the uncertainties from all sources are proposed to describe the meaning of quoted temperatures in phase equilibrium work.

A technique is outlined whereby the surface M-H relationship on manganese-zinc ferrite single crystals may be obtained using a signal averager to improve signal-to- noise ratio. Unwanted magnetostrictive components are removed by computer-aided Fourier analysis. The method is used to obtain a surface M-H loop using the longitudinal Kerr effect to detect the fluctuation in surface magnetization.

A resistance-thickness monitor is described for thin evaporated metallic films in which the power dissipation in the film is several orders of magnitude lower than comparable bridge monitors. Typical sheet resistance against thickness plots are shown for films of aluminium, copper and nichrome in the range 300-1500 AA.

A simple method of long-term tensile creep-testing of ceramic materials is described, employing frictionless knife-edge universal joints and a gripping system which minimizes nonaxialities. The apparatus has a maximum constant load capability of 100 kg and was designed for use up to 1000 degrees C to test glass-ceramic materials. Some results are given which illustrate the reproducibility of the method, and an estimation of the errors involved in strain measurement is made.

Two methods are described for stabilizing the output of an HCN laser: an automatic power control system suitable for use in a variable temperature environment, and an automatic frequency control system requiring stable laboratory conditions. The former can stabilize the laser output power to within +or-2% of a predetermined level for approximately 200 h. Some of the principles of operation are applicable to other devices.

An apparatus is described which enables measurements of magnetostriction to be made in intense pulsed fields up to 20 T. Resistive strain gauges are used to detect the strain in conjunction with an AC bridge employing synchronous phase sensitive detection. The apparatus is sensitive to strains of the order of 5*10^-6 and can be used over a wide range of temperatures. The errors which arise due to the pulsed nature of the field are discussed.

The electric field at a high voltage electrode is modified by corona discharge in the space surrounding the electrode. A knowledge of the resultant magnitude of the electric field is of value in the theoretical analysis of the corona. Systems of cylindrical geometry are of particular importance because of applications in electrostatic precipitators and in power loss from overhead transmission lines. The earlier methods of field measurement in corona discharges have not been suitable for measurement of the field strength at the electrode surface, especially in the case of power frequency corona. The paper describes a new technique employing a cylindrical rotating electrostatic fluxmeter. The device is capable of differentiating between conduction and displacement current when used as part of an active corona electrode.

A probe for use in measurements of contact potential differences (CPD) has been designed and constructed. The probe has the following unique features: (i) it is guarded against capacitive coupling between the probe and surfaces other than the sample; (ii) it can be heated so that adsorbed gases can be flashed off; (iii) it is excellent for use in UHV systems; (iv) it can be made small enough for nonuniformities in the work function of the sample material to be examined; (v) it is simple to construct. The effectiveness of such a probe to measure true CPD value was tested and the data presented here. Specifically the author is interested in: (i) the contact potential difference against the measured distances between probe and sample; (ii) resolution of the probe (the size of sample area contributing to the observed CPD); (iii) contact potential differences against amplitude of vibration of the probe and against the tilt of the probe about the axis perpendicular to the sample.

Small magnetic probes for use in a collisionless shock experiment have been constructed. The method of building the coil, connecting it to the oscilloscope, shielding and enclosing the probe, calibration, and testing of the time response with a fast square wave pulse and a sampling oscilloscope are described. These probes, with response times of <or=2 ns, have been used to measure correspondingly fast disturbances in an oblique shock wave.

A new electrostatic energy analyser is presented. It uses two sets of spherical grids. The first one is a retarding field arrangement in which the particles are decelerated down to energies close to zero. The transmission properties of the retarding field are presented. The particles enter the second part, an inverted spherical accelerating set which sharply focuses the low energy particles into the entrance aperture of a multiplier, whereas the high energy part misses the aperture. By cutting out the fast part, only a narrow energy band reaches the detector and a high signal-to-noise ratio results.

A symmetrical telecentric lens has been constructed from commercial optical components, and tested for use with the moire technique. The lens has been used, in conjunction with camera attachments for the measurement of elastic and plastic strains on both flat and curved surfaces.

Describes an analogue computing system for gaussian and lorentzian simulation of absorption circular dichroism and electron spin resonance spectra. The output is given either on a large multichannel monitor, showing each component and the total simulated spectrum, or on the recorder of any spectrometer with which the computer may be integrated, here a Spectronic 505 spectrophotometer. Gaussian analysis of the absorption spectrum of the trans- diaquatetramminechromium(III) ion illustrates the power of the system. Some problems in such 'many parameter' fittings are discussed.