Table of contents

Discusses the items appropriate to medical physics exhibited at the 1972 Physics Exhibition.

Discusses the various nuclear instruments, including counters, spectrometers, multichannel analysers, and radiation detectors displayed at the 1972 Physics Exhibition.

Discusses the instruments which can be classed as using electron optics which were displayed at the 1972 Physics Exhibition.

Reviews instrumentation displayed at the 1972 Physics Exhibition, under the headings electronics data analysis, optical data analysis and systems using lasers.

Two modified forms of a new type of electrostatic ion source are described. The one produces multiple beams of positive ions and in the other a wide ion beam is produced. The sources can be used for ion etching either a large number of small specimens or a large area specimen.

A simple and robust optical configurations for a two-dimensional laser velocimeter is described. It is of the 'real-fringe' type and makes use of non-interfering polarized beams to superimpose the two sets of fringes.

A description is given of a current amplifier, designed specifically for collecting and amplifying the currents created within solid-state devices. Designed for use with the Cambridge Instruments Stereoscan scanning electron microscope it incorporates facilities for superimposing the conductive and emissive mode pictures thereby enabling exact positioning of p-n junctions to be obtained by this technique. Accurate location of the p-n junction in gallium arsenide varactor diodes is given as an example of the use of the amplifier.

A compact gate valve for ultrahigh vacuum use with an 0.75 in diameter aperture and minimum length of 3.5 in is described. The valve is bakeable, open or closed, to 450 degrees C and has a demountable stainless steel knife edge and an OFHC copper pad. The closed conductance of the valve is less than 30 fl s^-1.

The optimization of the geometrical arrangement of a spherical grid retarding potential analyser is discussed. A high-resolution three-grid instrument is presented which may be obtained with simple modifications from standard LEED instruments.

A liquid helium level indicator is described which is cheap and simple to assemble and is suited for use with a small volume metal dewar system.

Some preliminary results on the comparison of scintillation efficiencies of scintillators based on two white oils are described. It is shown that a new solvent, technical white oil, has a better scintillation efficiency than that of medicinal paraffin. A possible reason for this higher efficiency is discussed.

Parallel, monochromatic light is incident on a laminar specimen of translucent and photoluminescent material. The light transmitted into a known solid angle is measured and, using assumed values of reflectivity and refractive index the relationship between flux and angle is analysed to give the optical absorption coefficient and photoluminesce efficiency of the material.

A random alarm is a signalling device with random interarrival times having a prescribed probability distribution. In this paper, a specific design for a simple, compact, electronic random alarm mechanism is presented. The design can accommodate any chosen continuous distribution of interarrival times, since these times are obtained by appropriate transformation in a device that produces the uniform probability distribution of some physical quantity. Nonstored-table varieties of this type may be constructed by combining an RC charging network with different types of potentiometers. A general prescription is given here for the output potential of the potentiometer as a function of the angle of rotation, where the angle is a uniformly distributed random variable. The ability of nonstored-table mechanisms to realize arbitrary distributions is dependent upon three theoretical asymptotic considerations concerning the normal distribution, the uniform distribution and independence. An empirical investigation with data from twists of a simulated potentiometer is used to verify that these results are sufficiently robust for practical application.

Describes a simple modification to the phase-shift technique for determination of radiative lifetimes. The time delay between the exciting and emitted radiation is measured rather than the phase lag, and this removes the necessity for accurate knowledge of frequency and permits operation at relatively low modulation frequencies. A circuit is presented which provides a modulating and a delayed reference waveform and which compares the phase of a signal derived from the emitted radiation with the reference. Some preliminary tests of the system are described in which it is shown that the time resolution, for a modulation frequency of about 50 kHz, is roughly 5 ns (corresponding to a phase shift of less than 0.1 degrees ).

The basic concepts underlying the extraction of a high current ion beam with low convergence from a duoplasmatron are discussed ion optically with the aid of a ray tracing method. The modified extraction system is composed of two cylindrical electrodes, one the anode and the other the extractor, and it is controlled by the application of a combined magnetic field and electrical field to this bipotential lens. The anode which is composed of a cone- shaped orifice and a cylindrical expansion electrode with a concave cap allows the satisfactory expansion of the high density plasma and allows extraction of laminated flow from the concave plasma boundary. Currents of 20 mA at 20 keV are obtained. The current density is measured by the erosion of a fine mesh and the machining of stainless steel inserted into the beam path. It has been shown that a high current ion beam with a laminated flow satisfying the space charge limiting current and with a highest brightness of 10¹¹ A m^-2 sterad^-1 can be extracted and is very useful for ions beam processing applications.

An electronic device is described which generates pulses at exponentially increasing time intervals. It was designed to provide time-mark pulses for a chart recorder where (i) accurate time recording was required, (ii) the rate of change of input signal to the recorder decreased with time and (iii) it was expedient to reduce chart speed during a run in order to conserve chart. Photoconductivity rise and decay and fluorescence decay are typical phenomena which produce this exponential type of record. The device can also be used to provide command pulses for digital voltmeters or printers. With slight modification it would provide repetitive trains of pulses suitable for time-making oscilloscope displays.

A Kratky X-ray small angle scattering camera was equipped with a semiconductor detector. Because the energy resolution of the measuring system is about 3.5% for CuK_alpha radiation, CuK_alpha - and CuK_beta -lines can be directly separated from each other, also the monochromatization of the primary beam can be carried out without any intensity loss. For this reason the intensity measurements are more reliable than those obtained using other systems.

High magnetic fields may be generated by means of one or more concentric plane helical solenoids. The paper discusses the mechanical stresses in these solenoids when they are mechanically homogeneous and isotropic and compares them with the stresses that result when anisotropy is introduced. Under a wide range of conditions the introduction of anisotropy significantly reduces the maximum stress. The use of these principles in the ANU 30T magnet is described.

The solenoid described here is the outer coil of a two coil system for generating a 30T magnetic field. Analysis showed that a homogeneous plane helix would be adequately strong. The Bitter principle of constructing a plane helix was chosen for practical reasons but difficulties arose due to loss of strength from the slits in the discs and the fact that circumferential strength had to be developed through friction between discs. The problems were overcome by adopting a design where each turn was made up of 16 discs interwound in a staggered pattern which dispersed the slits and provided adequate friction bonding. The effect of the slits is small reducing the strength to 15/16ths of an ideal continuous plane helix. It is shown that such a Bitter solenoid may fail either by expansion or by unwinding. The relevant factors involved in both modes are discussed and it is shown that unwinding is the most serious mode and cannot be remedied by increasing the number of discs per turn. A system of keying the end turns via torsion cylinders is described and illustrated. The solenoid is in fact a two-start helix with one turn each end four-start. Reasons for these features are described associated with current distribution and ease of insulation checking. The unusual construction technique is described and illustrated.

The most important practical aspects of the design of the inner solenoid are described as well as details of the manufacturing techniques used. Brief mention is made of other likely applications of this type of design.

The test conditions of the ANU 30T high field magnet are described and the most significant observations reported. The factor immediately limiting the maximum achievable field intensity is delineated. Conclusions are reached with regard to performance under different conditions envisaged in the future.

A new nondestructive method for grain-size analysis of ferromagnetic materials is described. The method is based on the measurement of the statistical behaviour of transitions in the ferromagnetic domains. A correlation is shown to exist between these transitions and the optically perceptible grain-size distribution of the material. The measuring apparatus is discussed in detail, accompanied by the results of experimental measurements. The instrument seems to be capable of estimating the relative grain-size distribution of technical steel with a differential accuracy greater than 0.5 degrees ASTM. The method can be used in industrial environments for the on-line measurement of steel quality, thus eliminating some of the common problems of optical grain-size analysis.

For pt.I see abstr. A71791 of 1971. The quadrupole field component of a nonuniform r.f. field can cause harmonic mass peaks. This effect is mathematically analysed. It is shown theoretically and experimentally that these spurious peaks can be suppressed by a d.c. drift field.

A proposal for coupling 15 MJ of energy initially stored in the Canberra homopolar generator to a load in about 1.0 ms is described. 22 MJ is first transferred to a coaxial inductor at a peak current and voltage of 1.5 MA and 190 V respectively. Fast mechanical switches which are being developed would open to produce a potential of 1000 V and a peak power of 15 GW into the load. Information is given on the operation of a small version of the system being used to supply 100000 J to a high power laser amplifier.

A stainless steel vacuum chamber has been designed for the observation of luminescence emission from liquid or solid samples in the temperature range 80-380K following irradiation by pulses of high energy electrons. The samples may be irradiated in the presence of any gas at pressures between 1 mu Torr and 760 Torr. At low pressures and temperatures radiative heating of the sample becomes important and leads to thermal gradient in the sample. This effect has been investigated and reduced by the use of a cooled 'heat shield'.

An apparatus for specific heat measurements in the liquid helium range is described. The continuous warming method is used with measurements of the temperature taken with the aid of a digital voltmeter. The apparatus gives a high resolution (0.5%) and permits one to obtain about 1000 experimental points per degree very rapidly. Furthermore the vacuum inside the calorimeter which is sealed at room temperature, is obtained by cryopumping. The convenience of the technique is demonstrated by giving results obtained on a mercury sample.

A method is described for the design of slotted disc velocity selectors for molecular beams. Special emphasis has been laid on the suppression of parasitic velocities, even in the case of small imperfections in the actual instrument. Suitable configurations with a minimum number of discs has been found with the aid of a digital computer. Results are given for a large class of selector types.

The design of a microwave spectrometer for use primarily by the analytical chemist is described, with particular emphasis on the way in which previously limiting problems have been overcome. Advances in the design of the sample handling facilities, the absorption cell and the data processing system are described in detail and the performance of the complete spectrometer is illustrated.

A method for measuring the extent of lateral diffusion in silicon is described. It is based on the use of an oxide mask in the form of a thin wedge and the measurement of the position of the junction along the axis of the wedge relative to a reference point. The results obtained for lateral diffusion are compared with the vertical junction depth in the same wafers and are found to be in good agreement with theoretical predictions.

An equation has been developed for computing the capillary depression of mercury in tubes by fitting an equation to tabulated data. This empirical equation reads, for standard conditions of sea level and 70 degrees F, h=((0.293₆r-0.423₂₅) Delta h²+0.225r³- 0.325r²+0.009r+0.130₆) Delta h/( Delta h²+r²) where h is the capillary depression, r the radius of the tube and Delta h is the height of the meniscus, all in centimetres. Capillary depressions can be computed by this equation within about 1 mu m.

A test chamber for conducting hertzian indentation-fracture experiments on brittle solids in a controlled environment is described. Facility is made to evacuate the chamber, to heat the specimen and to admit a reactive gas or liquid to the specimen. The design permits a large number of runs to be made quickly, with external control of the test conditions. Some results of hertzian tests on glass are presented to indicate the means by which data for a general fracture mechanics description of environmental effects may be obtained.

A neutral particle detector is described which consists of a set of thermocouple elements evaporated on to a thin mica disc supported at its edge. This design provides a high sensitivity over a large area whilst still having a reasonable short time constant (4.5 s). The device has been used to measure beam powers of up to 10 mW, whilst minimum detectable signal is below 0.1 mu W. Response is linear over this entire range. The unit is easily constructed, is quite rugged and its response is independent of background temperature.

A creep apparatus was built to operate uninterruptedly for several weeks at rarefied atmospheres of pressure between 100 mTorr and lower than 1 mu Torr. Creep rates of zircaloy-4 tested in 100 mTorr of argon were faster than creep rates of the same alloy tested in air. The slower creep rates in air were attributed to the formation of an oxide surface layer.

A tunnel diode oscillator is used to obtain accurate measurements of the capacitance of the plasma sheath surrounding a cylindrical Langmuir probe in a collisionless plasma. The probe is biased in the ion saturation current region with probe potentials ranging from 17 to 220 V. A comparison of these results with similar data obtained using a simple LC resonant circuit is made and shows the technique to be a simple, precise diagnostic tool which should be generally applicable both for laboratory and upper atmospheric plasmas.