Table of contents

Reviews the nondestructive testing technique of neutron radiography, and in particular to emphasize the industrial applications which are at present in use and which are foreseen in the near future. Applications in the fields of nuclear reactor technology, aerospace and medicine are illustrated in radiographs from a selection of the operating laboratories in the UK and USA. The projected growth of the technique is discussed.

A simple bubble chamber experiment is used to introduce the student to some basic ideas of elementary particle physics and special relativity. Measurements are made of the masses, lifetimes and branching ratios of certain short lived particles (the so-called 'strange particles') produced in nuclear reactions.

A proven design of a simple and economical liquid nitrogen cooled photomultiplier housing for use with side window photomultiplier tubes is described.

The absorption spectrum of iodine vapour in the neighbourhood of 5145 AA (Ar⁺ laser green line) has been examined to determine its usefulness as a filter to reduce parasitic light in Raman and Brillouin scattering experiments. An absorption cell 100 mm in length containing iodine vapour at 50 degrees C attenuates laser light at 5145 AA by a factor of greater than 10⁴. However, other absorption lines occur at -3 and +6 GHz from the laser frequency which limit the useful frequency range of the filter for Brillouin scattering. A large number of narrow, closely spaced absorption lines in the near frequency range (>or approximately=+or-100 AA) cause an irregular but relatively small distortion of Raman line shapes.

An automatic apparatus for measuring the heat deflection temperature of resins is described. It provides a continuous record of the variation of the deflection with temperature and, when the test is completed, automatically cools to a preset temperature the hot oil in which the resin bar has been heated.

An X ray goniometer is described in which the principal characteristic is that the sample, placed in a horizontal plane, remains motionless, while the X ray tube and X ray counter move symmetrically. This apparatus is specially designed for use with a high temperature X ray diffraction furnace associated with other techniques such as differential thermal analysis, thermogravimetry, etc.

A two-channel analogue boxcar integrator is constructed by using integrated circuits and MOST gates. A ratio of two NMR fee-induction signals can be measured and thus the spin-lattice relaxation time T₁ can be obtained without any calculation by comparing output voltages of the channels by the null method.

A circuit is described which gives an output voltage proportional to the square root of the input. This has proved useful in feedback temperature controllers to make the power developed in a resistive heater proportional to the feedback signal, and so give a loop gain independent of temperature error.

Gating waveforms suitable for switching selected values of a control parameter in oscilloscope XY displays can be produced from the timebase flyback trace in a circuit which incorporates a complementary transistor shaping arrangement and a common emitter switch driving a counter-decoder circuit.

A technique is described in which a preselected concentration of microparticles can be delivered reproducibly to a given region of a pulsed discharge. Particle-to-gas mass ratios of 60 are easily realized for nickel dust and argon at 2 Torr background pressure.

An Archimedes density apparatus using only standard laboratory apparatus and capable of the rapid determination of densities of samples weighing only 30 mg with repeatability better than +or-0.05% is described.

Errors are estimated for a linearizer utilizing two squaring circuits for straightening of the anemometer output characteristic and a strain line sequence circuit for final linearization. Calculations are based on a velocity range of 0.6-150 m s^-1 supplementing the error estimates by Bruun.

A simple inexpensive cold stage has been designed for the Hitachi electron microscopes. Through the use of a Teflon isolated specimen holder connected to a coolant tank by aluminium foil, base temperatures near to that of liquid nitrogen could be obtained.

A numerical method is presented for the double integration of an electron spin resonance spectrum in the presence of base line drift. The calculation is valid whether the spectrum is symmetric or asymmetric, e.g. a composite resulting from multiple paramagnetic centres. The base line is automatically corrected.

The modulation transfer function of a proximity-focused image tube with unoxidized K-Sb-Cs photocathode and an inter-electrode spacing of 2 mm has been measured with lights of different colours. As expected, the resolution has been found to improve with an increase in the wavelength of incident light. It has been noted that this improvement is more marked towards the red end of the spectrum. From comparison with theoretical results, the mean value and the standard deviation of the energy distribution of photoelectrons have been found to be about 0.6 and 0.3 eV respectively.

A time shared system in place of the commonly used space shared systems for two beams passing a wavelength calibrated scanning spectrometer is shown to offer advantages, both fundamentally and with regard to simplicity. A description of a newly developed system is given which has been employed successfully in infrared atomic emission spectra observations. The method can be applied to any spectroscopic range. Either comparison spectra or the well known interference fringe method can be used to display a continuous calibration along the chart against the unknown spectrum.

A compact, easily fabricated ion source for diffusion and other magnetoplasma studies is described. Construction details and radial ion current characteristics with applied magnetic field are given.

The design and operation of a very simple and cheap automatic level controller for liquid nitrogen within an enclosed or open dewar is described.

A method is described for the accurate generation of truly random binary digits at kilohertz rates by means of a circuit sufficiently compact to go on to a single printed circuit card. The method uses the odd-even criterion with a Poisson distribution obtained by counting random pulses from an electronic noise source. It appears to be capable of development to give considerably higher speeds.

A photodiode-operational amplifier circuit is described, with which the shot-to-shot energy variations of a pulsed laser system can be monitored. The system has a useful sensitivity over the wavelength range 330-1100 nm; this is sufficient, with suitable focusing optics, to monitor laser pulses of total energy as small as 1 nJ. The system is insensitive to ambient light conditions.

A novel instrument for measuring the magnetic moment of a small specimen of material is formed by applying AC techniques to the traditional force magnetometer (or Faraday magnetometer). The action of the instrument is analysed and an attempt is made to mention all the sources of error and practical difficulty that arise. The new instrument is closely related to the well known vibrating sample magnetometer (although they are at first sight quite different), so the discussion of the new instrument serves also as a discussion of the VSM. A constructed instrument having a sensitivity of 0.2 nA m² is described.

A method for the accurate measurement of the thermal resistance of rather thin samples of high heat conductivity is described. It involves a sandwich arrangement in which the thin sample is held between two thicker pieces of bismuth telluride. The thermal resistance of the sandwich is then found by Harman's technique, using the Peltier effect to establish a temperature gradient. The method has been tested experimentally for silicon at room temperature.

Describes an electronic instrumentation system which has been designed to study the photochemistry of gas reactions. The equipment can be used for time-resolved ESR dissociation-recombination experiments which produce transient paramagnetic atoms, and also for one- way photochemical reactions with paramagnetic intermediates. One novel feature is a logarithmic sampling mode which is useful when looking for ESR transients of unknown duration. Both the logarithmic and the normal linear sampling modes use short (1 mu s) sampling times. A discussion of signal-to-noise ratio as sampling times approach zero is presented, and prefiltering requirements for both the linear and the logarithmic sampling modes are considered. The equipment is being used both for Zeeman and Stark transition electron resonance studies.

A simple low-frequency hysteresigraph capable of continuously recording a series of well-defined B-H loops, both symmetric or nonsymmetric is described here. The hysteresigraph is programmed before starting the sequences with a simple read-only memory. It can be used for studying the validity of Preisach's theory, and can easily be adapted to various other problems.

Details of the electronics of a stroboscopic electron mirror microscope which can be operated at frequencies up to 100 MHz are given. The system is made up, for the most part, from commercially available building blocks and can be adopted for other types of electron microscopes including the scanning electron microscope.

With the aid of an electronic device the proton lock in the Varian HA-100 NMR spectrometer is maintained in spite of rapid and large changes in the audio modulation frequency from which the proton lock is derived. The electronic device converts the audio modulation frequency into a direct current, which changes the strength of the magnetic field proportionally.

The general principles of operation of the swept frequency acoustic resonant interferometer are outlined and its use for measurements of energy loss and velocity dispersion in the low megahertz frequency range discussed. A number of different variations on the design of the resonator are described. Data on a variety of chemically different systems are presented illustrating the range and versatility of the technique for measurement of samples with low acoustic losses.

The use of a modified Jamin interferometer for the measurement of electron density gradients in a transient plasma has been demonstrated using a small Z pinch argon discharge. The interferometer was operated with 632.8 nm radiation from a He-Ne laser, and an interference pattern was produced using wedge shaped plates. With both beams of the interferometer passing along the length of the plasma and separated by 3.8 mm, differences in electron density were measured, and hence radial electron density gradients were derived. Electron density gradients as small as 5*10²² m^-4 could be detected with good reproducibility. The Jamin interferometer used in this way was found to have several practical advantages over the Michelson and Mach-Zehnder interferometers, even for absolute electron density measurement. These advantages include simple alignment, fewer optical components, and a stable, easily viewed interference pattern even in the presence of mechanical vibration. The interferometer was also used to locate the position of the centre of the Z pinch discharge to within 0.2 mm.

An astatic magnetometer with feedback is described. A unique feature of the magnetometer is that its sensitivity and response time may be altered by a single switch, so that moments in the range of 5 G cm³-50 mu G cm³ can be measured, keeping the sample at a fixed distance from the magnetometer. It has proved particularly useful for experiments in thermal demagnetization of rock samples up to 1000 K. The specimens to be measured are located some 8 cm below the lower magnet of the astatic pair and a total moment of 50 mu G cm³ (50 nA m^-1) can be measured at 1000 K. Without the furnace with the sample 4 cm below the lower magnet a total moment of 1 mu G cm³ (1 nA m^-1) may be measured. The output is displayed on a digital voltmeter, but any other data logging device for on line processing may be incorporated.

Experimental measurements of the relative intensity of the escape peak produced in a Si(Li) X-ray detector agree quite well with a theoretical expression. The escape peak is not negligible in electron microprobe and X-ray fluorescence analysis. An approximate estimate of the size of the internal fluorescence Si K peak shows it to be small provided the detector dead layer is thin (0.1 mu m), and for most purposes it can be neglected.

An ultrahigh vacuum apparatus for clean surface studies of high resistivity photoconductors is described. The system is capable of making contact potential difference measurements with an accuracy of +or-0.5 mV. This system, which employs the Kelvin method, provides a stability of +or-1 mV over periods up to 24 hours using specimens with a resistivity of greater than 10¹⁰ Omega cm. Cleaning of the specimen surface is possible at any stage during the measurements using argon ion bombardment. The system is so designed that variations of both photoconductivity and contact potential difference can be monitored with time or as functions of the wavelength or intensity of the illumination over a wide range of temperatures (100-600 K).

An improvement in the rigorous control of high voltages for dielectric measurements is achieved by employing digital techniques in the development of a low-voltage controller for a generator of either the oscillator or electrostatic type. Principal advantages over a method previously described are the provision of a highly stable hold mode and the capability for very slow rates of voltage application. Comprehensive logic controls, incorporating essential safety features, allow fully automatic experiments to be performed, and a flexible design permits a simple addition to the equipment to increase the resolution if desired.

A radiometer described was developed in the Department of Medical Physics at Newcastle General Hospital. Its main purpose was to calibrate a high power monochromator for dermatological irradiations. Other uses include the measurement of total light intensity, energy measurements in spectroscopy, the calibration of thermojunctions and thermopiles, and total heat absorption measurements.

Magnetic probes are described for monitoring the maximum temperatures in samples irradiated in nuclear reactors. The specifications of the probes are: small size (25 mm*1.5 mm wires), easy reading, dependable temperature indication to within a few degrees. The measuring range extends in principle from room temperature up to 1100 degrees C. The reliability of the method is illustrated with in-pile measurements utilizing Ni-18.7 at.% Cu probes which cover the important range from room temperature to 130 degrees C.

A phase-sensitive detection system is described in detail for measuring electron-energy distributions using conventional Langmuir probes. A switching circuit is also discussed which enables the system to measure the DC characteristics. A typical result is presented and modifications are suggested to enable probe characteristics to be rapidly determined.

The frequency of eddy shedding by a circular cylinder at constant Strouhal number is shown to be suitable for the measurement of flow velocity. A wind speed monitor and regulator designed on this principle for an on-line experiment has operated successfully in the speed range 4-20 m s-1, and the system is adaptable to other speed ranges.

An inexpensive method has been developed for determining the size, velocity and direction of flight of particles in flames by photographic means. The method consists of superimposing two photographs separated by a variable time interval. A careful choice of film and the use of various filters have enabled this technique to be used in highly luminous flames. A quick method of data retrieval from the photographs and conversion into a form suitable for direct access to a computer is also outlined.

A description is given of some constructional features of a stabilizer devised for control of temperature limited emission current in demountable X-ray tubes with AC heated cathodes. Line voltage stability obtained was of the order 0.02% change in emission current per 20% change in line voltage. The emission current was maintained constant within 0.01% for at least two hours.

A newly developed high temperature gamma radiation probe for in situ determination of radioactivity in high temperature media is described. Some applications in the aluminium industry are demonstrated.