Table of contents

The methods of measurement of nuclidic mass and isotopic abundance by mass spectroscopy are reviewed. The various factors that limit the accuracy of these measurements are considered. Also studied are those factors that limit the sensitivity of the mass spectroscope. The ways in which mass and abundance measurements are used when a mass spectroscope is used for chemical analyses are discussed and the limitations of the various methods are considered.

A single beam spectrophotometer has been developed for the measurement of spectral attenuation coefficients of very low loss optical glasses in the wavelength range 400-1000 nm. The instrument has an accuracy to ±0·00005 cm⁻¹ when sample thicknesses of 20 cm are used. The basic stability of the instrument and the sources and effects of systematic errors have been investigated in detail. Some results are presented in the form of attenuation curves for four different low-loss optical glasses.

A method is presented for using commercial stereo tape recorders for the recording of Mössbauer spectra. The recorded spectra can later be played back into a multichannel analyser. This method not only allows calibration of the equipment simultaneously with the measurements, but also effectively doubles the working capacity of the analyser. An improved moiré velocity calibrator is described in an appendix.

A wide range of electron impact energies in the scanning electron microscope can be achieved by varying the specimen potential with respect to the gun potential. Bulk and thin film specimens can be examined and the method also enables a direct representation of potential distributions in electrode structures to be obtained. Some preliminary results are shown and the technique offers an extension of the applications of the scanning electron microscope.

A new method is described for determining the flux density distribution in magnetic electron lenses of finite permeability. The method involves a simple modification to the resistance network analogue of the magnetic circuit. Pole piece flux densities have been determined under normal and saturation conditions in a high power objective lens. The influence of pole piece saturation on the axial field distribution is discussed.

An electrical analogy for the experimental investigation of a physical field in nonlinear flow is considered, particular attention being given to the hydrodynamic field of filtration. A network with a specific configuration of discontinuous electrical nonlinear elements is introduced. It has been established theoretically that such a network of basic elements with the corresponding analytical shape of their voltage-current characteristics, acts very approximately as a homogeneous and isotropically conducting medium which satisfies the analogous electrical nonlinear law of flow. These considerations have been confirmed experimentally for a two-dimensional network with tungsten heating wires as the nonlinear elements. The accuracy of electrical modelling has been controlled on simple rectangular and cylindrical models analytically solvable also in nonlinear flow.

The systematic error induced in the readings of neutron moisture gauges by the variation in the dry bulk density of the medium is investigated theoretically. To obtain the correction for dry bulk density in any gauges, two independent measurements have to be performed. The correction is calculated by means of three-group theory with group constants evaluated from multigroup moment equations.

A modified diaphragm cell has been designed for diffusion measurements at temperatures up to 60°C. This new design eliminates the disadvantages inherent in the conventional diaphragm cell technique. The new design has three compartments, and the composition in the top compartment of the cell is measured continuously during the diffusion process. This design allows for the expansion of the test solutions during temperature equilibration and also for volume changes on mixing during the diffusion process. The cell, although applicable to both inorganic and organic systems, must be calibrated by reference to a known system, e.g. KC1 in water at 25°C.

Expressions are derived for turbulence spectra measured with a single hot wire and wires in an X-array, and are applied to the problem of measurement of spectra at small scales. Isotropic turbulence and Pao's form for the three-dimensional spectrum are assumed. Calculated curves for one-dimensional spectra measured with a single wire and an X-array are presented. Experimental data in good agreement with the single wire calculations are shown. The calculations show that both one-dimensional spectra measured with the X-array are contaminated by crosstalk from the other component. The effect is more serious for the longitudinal spectrum and depends on array geometry and the Kolmogorov microscale.

An apparatus designed to measure the dynamic viscoelastic response of polymer melts is described. The sample under test is held in a cone and plate assembly, and small strains varying sinusoidally are introduced to the lower platen. A novel inexpensive transducer system is described for measuring oscillation amplitude. Dynamic elasticity G prime and viscosity η prime can be measured over a frequency range 1-10 Hz and at temperatures up to 350°C. Results are illustrated by measurements on two commercial grades of polyethylene, differing widely in molecular weight. Correlation between dynamic and steady-flow measurements is discussed.

This instrument will measure the viscosity and elasticity of polymer melts over the shear rate range 10⁻³ - 1 s⁻¹ at temperatures up to 300°C. The system is driven by ten synchronous motors and torque values are measured by a transducer. Use of this principle makes it possible to fit separate heaters in the cone and the plate, so improving greatly the temperature uniformity in the sample. Illustrative results for polythene and poly (methyl methacrylate) show good agreement with viscosity measurements at high shear rates made by the complementary technique of capillary viscometry. Time-dependent behaviour is briefly discussed.

The power supply for a microdifferential thermal analyser is described; it is novel in that it is based on solid state circuitry incorporating silicon controlled rectifiers, by means of which the duration of the heating pulse can be varied, so making it possible to use electronic circuitry for temperature programming.

A modification of the well-known Ramsay and Young method is described for the measurement of the vapour pressure of liquids. The method is simple to operate, and by restricting the length of vapour path, has been found suitable for reliable measurements to a lower limit of about 0·04 torr. The vapour pressure of tertiary butyl titanate has been measured from 0·06 to 10 torr, the vapour pressures of n-hexadecane and methyl laurate in the approximate range 0·04-200 torr, and those of chlorobenzene and bromobenzene from 16 torr to atmospheric pressure. Comparisons are made with literature vapour pressures for these materials.

Some simple but adequate methods of orienting and polishing large single crystals for ultrasonic measurements are described. These methods are useful for a variety of materials, particularly for metals and ionic crystals. Included are an x-ray method of measuring orientation and a description of fixtures and procedures involved in polishing. The use of these techniques on low lineage crystals can result in orientation accuracies of less than ½°, flatness of 5 × 10⁻⁶ in, and parallelism of 2 seconds of arc with moderate means and effort.

A simple and inexpensive means of studying samples containing water in a scanning electron microscope is described. The sample is maintained at a low temperature by thermal isolation in the specimen chamber. Micrographs of ice and clay with a high water content are presented.

An air-operated device is described for observing the output of pressure transducers when subjected to pressure rise times such as those experienced in short-duration aerodynamic testing facilities (in particular, the hypersonic `gun' tunnel). Some results of its use with an unbonded strain gauge pressure transducer are presented.

An apparatus for repeated cleavage of rocksalt crystals in ultra-high vacuum is described. During one vacuum cycle, 10-15 clean and `splinterless' substrate crystals have been achieved. The whole apparatus was made for use with a Varian VI-12 ultra-high vacuum system capable of reaching a pressure in the 10 ptorr range.

A proportioning furnace temperature controller having continuously adjustable bandwidth is described. The principal feature of this instrument is the power control of a resistance heating element by a flexible and non-critical circuit design which provides high performance at modest cost.

An apparatus is described which will accurately project a drop of known size with a given velocity. This is achieved by placing the drop on a wire beneath a small metal cylinder which is then allowed to fall freely under gravity and abruptly stopped when the required velocity has been attained.

Numerical values are tabulated which allow the temperature profile to be determined along a uniform specimen which has one end held at a fixed temperature and a steady heat input applied at the other. The tabulated values are functions of the three relevant variables, namely time, distance along the specimen and thermal diffusivity.

Generators of high-voltage pulses of sub-microsecond duration are most conveniently based upon the discharge of a coaxial cable through a spark-in-air switch. Several advantages result from the decision to charge up the outer, rather than the inner, conductor. Insulation problems are reduced as are also constructional and operational details. The most important advantage, however, lies in the ability to vary the pulse length. Rise-times of a few nanoseconds are easily obtained with the proposed generator.

A linear heating rate temperature controller for use in thermoluminescent studies is described. It provides a range of heating rates from 0·2 to 100 degC s⁻¹ with a deviation from linearity of no more than 0·2 degC. It is capable of operating up to temperatures of 750°C.

A radio-frequency method utilizing the fact that rapid changes in permeability occur at the Curie point is described. The circuit used is essentially a temperature-compensated marginal oscillator. Powders or small samples of any shape may be used. The device is fully automatic and has no moving parts.

Field modulation is used with pulsed electron spin resonance apparatus to measure the relaxation time T₁ of weak but easily saturable paramagnetic resonances. Both a boxcar integrator and lock-in detector are used to recover the field modulation signal from the noise. The method works best for T₁ between about 1 μs and 1/10 of the field modulation period (e.g. approximately 1 ms for 100 cycles) but it may be used to measure longer relaxation times also.