Table of contents

A new magnetometer is described for measurement of the permanent magnetization of small particles of magnetic material and for the examination of magnetized surfaces. It has been developed for investigations in rock magnetism involving small grains of natural magnetic minerals, both after separation from the parent rock and while still in place in a rock surface. The detector is a small spherical magnet on one end of a fine, horizontal glass arm, the other end of which is attached to a vertical torsional suspension. A torque is produced about the suspension axis when the magnet is in a horizontal magnetic field with a vertical gradient, such as is produced by a magnetized particle in the vicinity of the magnet. Particle magnetizations of the order of 10^-9 G cm³ (10^-12 A m²) may be measured, and, under appropriate conditions, estimates of low field susceptibility of the particles may also be made.

An apparatus for measuring magnetic susceptibilities by the Faraday method with a resolution of 10^-10 e.m.u. g^-1 has been constructed. It is suitable for the measurement of susceptibilities by the substances with either weakly diamagnetic or strongly paramagnetic (antiferromagnetic) properties. The design enables exchange of samples whilst maintaining liquid helium in the Dewar; the cryostat can therefore be run continuously. The temperature of the sample is easily varied over the whole temperature range 1.6-300 K. A temperature stability within 0.01 K at low and 0.1 K at high temperatures is obtained using very simple equipment. The compact construction of the insert Dewar allows a small inexpensive magnet to be used.

A dynamic instrument for determination of magnetocrystalline anisotropy energy has been developed. The sample is forced to oscillate with a fixed frequency and amplitude in a homogeneous applied magnetic field. The phase and the amplitude of oscillation for the perpendicular component of the magnetization vector, which determines the anisotropy energy, is detected in a suitable pick-up coil arrangement. The sample oscillation is obtained through an electrostatic excitation of a resonance mode in a high Q mechanical oscillation unit. The sensitivity of the instrument corresponds to the signal from a permanent magnet of moment 3*10^-6 emu (3.8*10^-15 V s m). This is equivalent in magnitude to the signal from a 1 mm spherical sample, which has a 0.02 Oe anisotropy field, exposed to minimum applied field (4 pi /3)M_s.

Correction of errors in measurement of X-ray diffraction intensities by integrating microdensitometers which arise from nonlinear characteristics response curves and a finite size of the cross section of the transmitted light beam is discussed.

An automatic, horizontal axis X-ray diffractometer is described employing Bragg-Brentano para-focusing geometry, with post diffraction monochromatization. The diffractometer is specially designed to examine either the top free surface or, in the present work, the lower surface of a liquid. The lower surface is irradiated through a beryllium window in the base of a cell. Measurements on liquid mercury at 23 degrees C indicate that the technique produces diffraction patterns in good agreement with those of other workers.

A new theory of coincidence errors in automatic particle counters is proposed. Expressions are given relating the true particle count to the observed count at zero threshold. For the Royco PC-200 particle counter the coincidence error curve is determined experimentally, and, throughout the range of count levels investigated, the new theory is found to be closely applicable, whereas previous theories are applicable at the lower count levels only.

The charge associated with an insulating sheet is monitored by scanning the specimen underneath a capacitive probe coupled to a detection system of very high input impedance. The charge distribution is displayed either on an XY recorder as a deflection modulation of the raster pattern, or with a cathode ray oscilloscope operating in the beam intensity modulation mode.

An automatic-programming and data-logging system for use in isothermal and adiabatic calorimetry is described. The requirements of each calorimetric system are outlined, and the composition of the complete system is detailed. The sequence of operation of the control logic behind the automatic system is described fully in an appendix.

A channel plate requires outgassing by electron bombardment to stabilize its gain. During the outgassing large quantities of gas are evolved This paper describes the analysis of the evolved gases with a low-resolution mass spectrometer. Hydrogen, CO, CO₂ and hydrocarbons are the most plentiful outgassing products. The dependence of outgassing rate on channel plate voltage is examined for each of the evolved gases.

A method is described for suppressing impulse interference in a signal detection system by recognizing it as a non-Gaussian contribution, not possessing any of the expected signal characteristics. A digital implementation of the method is presented in detail. The performance of a complete signal detection system employing signal integration together with impulse interference suppression is discussed.

A spot-welding device is described which uses thyristor triggering. The array has small dimensions and is employed for welding thin wires and foils used for voltage and current connections on various small samples, as well as thermocouples. Basic advantages of this device consist in the reproducibility of results as well as the complete control of dissipation energy.

An optical slit that does not use a window material but which nevertheless has a low conductance for gas flow is described. It has a high efficiency ( approximately=40%) for transmitting vacuum ultraviolet light.

An apparatus for measuring the pore-size distribution over the range 300-7 mu m is described. The apparatus is constructed from a modified Amsler machine and the results are in good agreement with those obtained using a high pressure mercury porosimeter over the common range. The new instrument detects pores which are too large to be detected by a standard high pressure apparatus.

A new substandard low level light source, which is not subject to light induced luminescence, has been developed and tested over a period of two years. The source described here is particularly suitable for the routine calibration of thermoluminescent dosimetry systems.

The use of porous substrates made from medium grade (180-220 grit) slip stones is described. Specimens attached to these with wax thicknesses of much less than 1 mu m have been polished to less than 10 mu m in thickness and parallel to 1 mu m in 2.5 cm.

Methods are described for preparing disk specimens containing carbon fibres with any orientation of fibre axis. From these disks thin sections containing large electron transparent areas in each of several fibres can be produced by ion beam machining.

An optical gate using a mixture of silicone oils has been made. The gate enables photographic plates to be used as diffracting screens without unwanted phase effects arising from the nonuniform optical thickness of the plates. Details are given of the procedure used to find a precise optical match between the plates and the oil. It is estimated that the variations in optical thickness of the plates in the oil can be reduced to considerably less than the Rayleigh lambda /4 limit. The method does not depend upon accurate measurements of thickness or refractive index of the glass or emulsion of the plates.

The transmission characteristics of a mechanical velocity discriminator are analysed and a discriminator design is described in which the ratio (minimum velocity of transmitted beam)/(rotor speed)=5.99*10³ cm rev^-1. Preliminary results of its operation in conjunction with a fast caesium atom beam are presented.

A simple laboratory device for the rapid preparation of high quality polished surfaces from relatively rough metal specimens has been described. Even though, compared with other methods, high current density is used deep polishing takes place without pitting.

An apparatus for automatic driving of a fore prism grating spectrometer is described. Stepping motors controlled by a program recorded on a photographic film ensure a good reproducibility of spectra obtained without manual operation.

Observations are presented of the density-exposure and reciprocity law failure characteristics of Polaroid type 57 and type 52 film when used in conjunction with NE421 and NE905 thermal neutron intensifying screens. The NE421-type 57 combination proved to be the fastest radiographically and also has extremely good reciprocity failure characteristics, which makes it most useful for radiography with low intensity neutron beams.

A simple procedure for obtaining the distributions of magnetic hyperfine fields from Mossbauer spectra is outlined.