Table of contents

In a typical experimental situation, the overall signal/noise ratio is determined by the signal source in conjunction with a linear amplifier. The optimization of the parameters of the amplifier in relation to those of the signal source are considered, with particular reference to the frequency range of DC to a few hundred kilohertz.

A commercially available continuous flow cryostat (Oxford Instruments CF 100) has been coupled to a Philips PW 1410 X-ray emission spectrometer by means of a few simple modifications. The technical details of these modifications are described and practical uses for the future are suggested.

An inexpensive, compact and efficient catalytic converter for removal of ozone from the cooling air stream of compact arc lamps is described. The device uses no power and requires no regeneration. Test results are presented showing essentially complete removal of ozone from the cooling air stream of a typical 150 W xenon arc lamp.

The circuit described controls the heating power of a thermostat by the variation of the cyclic ratio of a multivibrator. Its efficiency is high. It allows temperature stabilization to 1 mK for 20 J and better than 10 mK for 3 a.

A device is described which uses three mirrors to vary continuously the angle of incidence while preserving the direction of incident radiation. This device may be used for the measurement of reflectance in the vacuum ultraviolet regions.

Most multichannel analysers have the facility for plotting accumulated data on an XY recorder. Usually, without the use of accessories, the data are plotted as a continuous line. There are many occasions however, when it is convenient to plot the data as points so that the graph plotted is a replica of the spectrum shown on the CRT of the multichannel analyser. A circuit which allows such a plot to be obtained is described.

A new instrument capable of high resolution (0.1 mu m) scanning electron microscopy and selected area Auger electron microscopy as well as fast (100 s) Auger imaging facility at lower resolution (5-10 mu m) is described. The instrument is a true surface analysis tool and is completely of ultrahigh vacuum (UHV) construction. The approach of using two separate electron guns is explained and some results are presented. Some problems of proper Auger imaging are discussed. A special specimen transfer facility for UHV is also described.

Perturbation equations describing the response of hot wires and hot films operating in a simple constant temperature circuit are developed. The heat transfer model shows that at low frequencies (a( omega /K_s)¹2/<or=1, where omega is the perturbation frequency and a and K_s are the substrate radius and thermal diffusivity respectively) the hot film responds like a hot wire. At high frequencies (a( omega /K_s)¹2/>>1) the hot film rolls off at 30 dB/decade. Experimental measurements of the circuit frequency response to a voltage perturbation for both a hot film and a hot wire show good agreement with theory if the calculations use the measured probe time constants, and when thermal end losses are taken into account.

A gas microwave bridge spectrometer for the study of the shape of overlapping lines at pressures up to 1 atm is described. A novel free space cell is used, which has low transmission losses (below 5 dB for the 8 m cell) and minimizes reflections from the cell walls. This enables absolute determination of the absorption and refraction of gases when high sensitivity and resolution is required. Preliminary measurements are reported.

A superheterodyne emitter-receiver system is described which may be used either as a swept frequency or a cavity locked coherent microwave source in the full x band. Constructional details are given and information about spectral purity (Allan variance) and longterm stability for both modes of operation are reported. The performance of the system is demonstrated by its use as a high sensitivity high resolution Stark or source modulated microwave gas spectrometer and as an ESR spectrometer.

A new apparatus allowing formation of symmetric and asymmetric lipid bilayers by joining two monomolecular layers is proposed. A detailed description of this apparatus is given with a set of results demonstrating the validity of this process.

The optical configuration comprises an imaging lens with the reference point source on the optical axis in the centre of the exit pupil of the lens. The spatial frequency band is determined by the aperture and is independent of object size. In spite of the similarity to inline image plane holograms, image and intermodulation wavefront terms are separated by means of slit apertures in the recording step and matched spatial filters in the reconstruction step. Reconstruction is performed with thermal light, the interferograms can be displayed or printed directly on photographic paper.

A simple and reliable method to transfer irradiated specimens at liquid helium temperature without any intermediate warming is described. The transfer is performed under the helium gas atmosphere at room temperature using a small vacuum-insulated metal Dewar and consumes only a small amount of liquid helium.

It has been shown that incorrect crystal setting decreases the resolution by an amount which can be calculated from a superposition rocking curve model. The reasons for the occurrence of a doublet peak in an (n,-n) rocking curve under a special two slit arrangement are discussed. The doublet separation is used to determine the tilts of the crystals and their rotation axis. A detailed description of aligning the double crystal spectrometer is given.

For linear transfer conditions and objects with isotropic statistics, both the sharpness of the point spread function and its departure from rotational symmetry show up in the shape of the autocorrelation peak of the electron micrograph. It is therefore suggested that this function be used for interactive or automatic focusing and stigmating of instruments with online digital image readout. Model computations suggest that this method works satisfactorily at reduced levels of exposure.

A device for the separation of spherical from nonspherical particles using the principle of rolling the spheres down a rotating inclined plate is described. With a slightly modified technique, the principle can be applied where the nonspherical particles also have some ability to roll. The device has been evaluated for glass particles using mixtures of spheres and 50% by weight of various other shapes. The percentage separation has been measured for varying rates of feed and for varying angles of inclination of the plate. Efficient separation is achieved for the particle sizes tested (0.5-1.68 mm), but further evaluation will be necessary to determine the limits of size to which the method can be applied.

A method is described to calibrate UV standard lamps which emit line radiation with respect to irradiance. The calibration is based on a comparison with the 140 MeV electronsynchrotron of the Physikalisch-Technische Bundesanstalt (PTB). The relative spectral intensity of the synchrotron is calculable, the absolute value is determined by comparison with the spectral radiant intensity of a blackbody source in the wavelength range 350-600 nm. As an example the results of a calibration of a mercury low pressure lamp are given.

For pt.I see abstr. A78411 of 1970. A method described earlier for growing sets of oriented thin single crystals from a common seed crystal has been improved considerably with regard to the homogeneity of the samples, and a device is described for growing secondary seed crystals with any desired orientation relative to the primary seed crystal.

A homogeneous field sector analyser of simple design giving first order double focusing and with 90 degrees deflection is described. Constructed for use with the Cavendish high voltage electron microscope for beam energies up to 750 keV, it has a theoretical resolution of 9 eV with a 10 mu m selecting slit and aberration less than 0.3 mu m. An electrostatic deflection system is included to provide for the scanning of small energy changes and to enable compensation of periodic fluctuations such as 50 Hz modulation. The analyser is a convenient way of examining the quality of the HT supply. The full width at half maximum of the beam energy spectrum was found to be 80+or-5 eV at 300, 500 and 700 keV and this has now been improved to 40 eV using the analyser as a monitor. Characteristic (inner shell ionization) losses can be readily detected from specimens much thicker than those used at normal microscope voltages. To date, K losses from boron to copper, L losses from nickel, copper and silver, and M losses from silver have been detected.

An instrument for measuring the absolute thermal expansion of solids up to 1000 degrees C is described. A sensitivity of 10^-8 degrees C^-1 was achieved by means of a frequency stabilizer laser and a polarization interferometer. Details of the laser stabilization technique interferometer, automatic polarimeter, sample chamber and preliminary results on tungsten are given.

Describes the design of an easily built and sensitive molecular beam detector suitable for molecules which can be handled by the surface ionization process. It has the advantages that is uses a round hot rhenium wire ensuring an ionization yield of 100% for most molecules, and that the whole system including ion deflection optics, quadrupole mass filter and ion multiplier can be positioned perpendicular to the molecular beam. The wire is placed in such a way that direct illumination of the multiplier is avoided. The theory of the ion deflection system is extensively treated and the results are compared with the experimental data. A maximum detection efficiency of 85% is obtained. The suitability of the combined round hot wire and ion deflection electrodes for an electron gun is under investigation).

Describes a solid state backscattered electron detector that has been developed at Harwell for use in a scanning electron microscope. Applications of the method of detection are discussed and examples of the three principal uses are shown. These are in the display of atomic number variations, examination of crystal quality and in topographical examination of insulating specimens.

A method for measurement of refractive index and birefringence of transparent solids during transient and dynamic mechanical tests is presented. The method of is based on interferometric measurement of the retardation of light travelling through the specimen under two different incidence angles. In addition, thickness variation during deformation-leading to Poisson's ratio under certain conditions-can be calculated. The method was applied to polymethylmethacrylate and polycarbonate samples subjected to uniaxial tension.

The usefulness of the magnetic defocusing technique in accurate measurements of light intensities is shown to be limited by the production of a 'fringe' area on the photocathode in which the overall counting efficiency varies rapidly with position, and in which the pulse height distribution is degraded. It is also shown that the magnetic fields used in this technique reduce the proportion of ion afterpulses in the output signal.