Table of contents

A brief account of the Mössbauer effect and its applications is given. The most popular types of spectrometer are described and their deficiencies considered in some detail. The problems of the reduction of data are dealt with, and the problems of obtaining spectra at low temperatures. A final section considers the choice of counters for transmission and backscattering methods. between the nucleus and the atomic electrons, called the hyperfine interactions. The strength and nature of these interactions depend strongly on the electronic, chemical and magnetic state of the atom. Thus a spectrum of the nuclear resonant frequencies can give valuable information about the atom and its surroundings. The hyperfine interactions can be understood by reference to figure 1, which is drawn for the case of ⁵⁷Fe. On the extreme

A local oscillator system has been built for radio-astronomy spectral-line observations at frequencies of about 100 GHz. The system switches between two locked frequencies separated by 80 MHz. A 102 GHz signal source is phase-locked to the third harmonic of a locked source at 34 GHz, for which commercial phase-locking equipment is readily available.

A direct method for obtaining a desired variable from the output of a nonlinear transducer is proposed. As the method preserves the basic accuracy of digital voltmeters it could have general value for precise analogue computing. Particular reference is made to the direct indication of temperature using a thermocouple as the transducer.

Describes a set-up designed to realise the coupling of thermogravimetry and X-ray diffraction methods. It consists essentially in a symmetrically moving theta , theta X-ray diffraction source and counter goniometer, a controlled high-temperature and pressure cell, and a zero microbalance adapted for coupling. This apparatus allows the simultaneous recording of data relative to the mass and the structural change of a single sample. Possible applications lie in the study of nonstoichiometric phases, nonstable intermediate phases, correlation between structure transformation kinetics and decomposition kinetics.

A simple technique employing a light emitting diode has been devised which can be used to investigate certain faults which may occur in the production of pulsed laser holograms. The device, which may also be used in sensitometry, is cheap, extremely reliable and capable of easy modification to allow different light outputs.

In quantitative electron microscope microprobe analysis using the 'ratio method', standards containing known relative amounts of two or more of the sought elements are required. Techniques are described for the preparation of such standards using suitable oxides, hydroxides or silicate minerals. The method has been verified for five series of standards containing Si plus one of Mg, Al, Ti, Fe and K. Plots of characteristic X-ray intensity ratio against atom ratio were linear with coefficients of variation in the slopes between 1.7 and 5.0%. An example shows the application of the method to the analysis of kaolinite particles.

A batch processing autocorrelator is described suited to the analysis of stationary signals whether continuous or discontinuous in time. Input signal frequency may extend up to 75 MHz.

A method of separating k alpha ₁, k alpha ₂ X-ray doublets, where both overlapped lines are symmetric, is applied to the problem of the separation of overlapped X-ray Compton profiles. The technique avoids the accumulation of statistical errors characteristic of the commonly used iterative method of Rachinger (1948).

The sensitivity of the resolving power of electron microscopes to ambient AC magnetic stray fields is well known. The highest permissible values of stray fields are fairly low and it may be difficult to find a suitable site for a microscope in normal laboratory conditions. A brief description of a device is given which reduces the disturbing effect of these stray fields by the method of automatic compensation. The device was tested on a JEM 6A transmission microscope. Even in an AC field as high as 24 mG (peak to peak) substantially higher resolving power was attained than that guaranteed by the manufacturer. Possible applications of the device to other electron beam instruments and in different magnetic stray fields are briefly discussed.

A small electromagnet system with circular plane-face 38 mm diameter pole pieces is described which bends 400 keV protons or deuterons through 7¹/₂ degrees and separates them cleanly from unwanted beam components. It costs Pounds 300, which is under one-fifth the price of a conventional arrangement.

The design and operation are described of an optical cell and supporting apparatus for making precise absorbance measurements of dilute aqueous solutions over the temperature range 25-250 degrees C. Results obtained in studies on the dissociation of salicylic acid and of the o-phenanthrolium cation show that precision of better than +or-1% in absorbance is obtainable over this temperature range.

A simple low-cost peak detector for continuous mass spectrometric experiments is described. The circuit is suitable for use with insufficiently stabilized mass spectrometers, where continuous long-term measurement of the peak signal from a single component of the spectrum is required.

A calculation scheme for the evaluation of hyperfine field distributions from overlapped Mossbauer spectra is being proposed. A different procedure for the same purpose has been used by Window (1971). Based on simulated Mossbauer spectra both methods are applied for three special cases. The obtained results are compared and discussed.

The possibility of direct thermal pumping of gases under molecular flow conditions using directed molecular scattering from certain surfaces is considered. Several simple thermomolecular pumps, using carbonized nickel for active surfaces, have been built. Single-stage pressure ratios in excess of 1.3 have been obtained. A multistage window device has also been successfully tested.

A method of constructing Rogowski coils is described which eliminates coil failure due to insulation faults.

An oscillating cup viscometer has been constructed to determine the viscosities of molten copper alloys in the temperature range 232-1250 degrees C. The entire assembly is contained in a vacuum of 1 mu Torr to minimize both air damping of the oscillating member and oxide formation of the molten material. The rotational movement of the torsional pendulum is observed by reflecting a laser beam from a mirror mounted on the pendulum assembly to a film strip. The end of a swing is sufficiently slow in motion to expose the film at that point. The damping of the pendulum is an accurate and direct measure of the viscosity of the fluid contained in the cup.

When the electrical and thermal properties of resistor materials are temperature dependent the operating temperature of the resistive conductor may be predicted by a graphical method. In unusual cases of dependence, as with the electrical resistivity of pure iron, the method indicates that multiple solutions may be possible. On theoretical grounds it is predicted that two such solutions may coexist in different zones of a single resistor. When the voltage is varied the interzone region migrates along the resistor to keep the current constant. The design and testing of three such types of experimental resistor are reported. The 'zoning' phenomenon is found to occur as predicted.

The frequency response has been determined for two probe designs used for cardiovascular measurements: one conical, the other cylindrical. The frequency range was 1-1000 Hz using an oscillatory velocity component superimposed on a mean flow; the test fluid was water. The amplitude response to the fluctuating component was found to depend on the Strouhal number (a normalized frequency) and was almost independent of the amplitude of oscillation. At small Strouhal numbers the behaviour is quasi-steady; at higher values the sensitivity progressively diminishes, but for the cylindrical probe there is an intermediate region of increased sensitivity. The oscillatory component had no effect upon the conical probe sensitivity to the mean velocity, whereas the cylindrical probe showed an increasing apparent mean velocity for some conditions. Fluctuating velocity values were inferred from steady flow calibration data and, therefore, a detailed comparison was made between such calibrations in blood and water.

A method is presented for measuring the relative intensities of sensitized and resonance fluorescence in alkalis by using a pulsed nitrogen pumped dye laser and gating the output pulses from the photomultipliers. Measurements show the system to have a high signal-to-noise ratio and much improved sensitivity over previous methods.

A diaphragm cell for experimental determinations of diffusion coefficients at elevated temperatures, up to the normal boiling point, was developed and is described. The cell consists of three compartments and is designed to operate at pressures up to 25 lb in^-2 gauge. Two compartments separated by a porous diaphragm constitute the diffusion cell proper. The third compartment is used for storing one of the test liquids during the preheating period. At higher temperatures the cell is operated at pressures sufficient to suppress the boiling, which would interfere with the diffusion process. The operating procedure is described in detail.

A magnetic analyser has been used to determine the charge states of the ions produced by the oscillating electron electrostatic ion source. With the appropriate gas the predominant ions were H₂⁺, He⁺, N⁺, and Ar²⁺, but higher charge states were seen and these increased with increasing source power.

The design and construction of a computer-controlled X-band ENDOR spectrometer are described. The instrument operates in the RF band 3-39 MHz with a maximum power of 1 kW, corresponding to fields of 80 G peak to peak in the cavity. Details of a new construction for the microwave cavity are given. A minicomputer is used for control of the experiment and data acquisition, processing and display. Examples of the performance are presented.

The problems of obtaining high homogeneity air-cored magnets with side access are considered. It is shown that sixth order corrected split pair magnets can be built by taking a notch out of the windings. Design tables and curves are given.

A graphite tube electric furnace has been designed to facilitate measurement of electrical properties of small refractory samples at high temperatures. Conductivity data are obtained with the sample at a uniform temperature in the central zone of the furnace. Thermal EMF data are obtained with the sample in a controlled and measurable temperature gradient at either end of the zone. The furnace tube is mounted axially in a water-cooled cylindrical chamber filled with argon or nitrogen at atmospheric pressure. A novel feature is that, with no thermal insulation other than an annular space round the furnace tube, fast rates of heating/cooling are possible, and thermal equilibrium can be achieved rapidly (in 3 min) at any desired sample temperature up to 3000 degrees C.

Reports an investigation into the use of a cheap electrolytic spirit level (vial) to detect change of building tilt due to soil subsidence (a few milliradians in a temperature environment of at least -5 to 30 degrees C). Vials of this type were found to have a wide spread in tilt sensitivity (for example +or-25%) and a significant tilt temperature coefficient ( beta ) of about -1% degrees C^-1. An open loop tilt monitor requiring calibration with each vial is described; readings can be taken quickly, it has linearity of about +or-2% and employs an oscillator with negative source resistance to reduce beta to -0.1% degrees C^-1. In a novel closed loop tilt monitor a vial is mounted on a piezoelectric bimorph and the voltage applied to the bimorph (being the output) is adjusted automatically to bring the vial to a horizontal position; linearity is about +or-0.5%, beta has a value of -0.1% degrees C^-1 (without a special oscillator), but the system takes as much as 10 min to settle after large disturbance of the sensing head, which makes it unsuitable for the particular application. Both experimental monitors experience tilt offset of about -10 mu rad degrees C^-1.

A linear direct reading conductance amplifier which is capable of following conductance changes due to chemical reactions in solution is described. It utilizes the simplifications in circuit design offered by operational amplifiers and has a sensitivity of 0.05% in each of the six ranges covering 0.025-10^-7 Omega ^-1. Reactions with half-lives from 2 ms to several hours may be followed.

A fast, inexpensive and simple pulse-height analyser as been developed for the analysis of the pulse-height distribution from a standard X-ray scintillation counter in which the pulse shape is controlled in the preamplifier.

A stage with a very regular translating motion has been built for taking X-ray images of lattice defects in large crystals. A high precision micrometer self-guiding screw and a nut with clearance adjustment locked by two lateral bolts exactly aligned with the rotation axis have been used. The position of the stage is secured without stress.