Table of contents

A servo-controlled pressure stabilizer for operation at pressures in the region of 1 torr is described. The design adopted allows for the correction of long (>1 sec) time lags whilst using an a.c. servo system. The operation of the stabilizer has been analysed and details are given of the practical arrangement and the performance. The operational stability of 1% which has been achieved is limited only by the vacuum gauge used for detecting pressure variations.

A simple feedback integrator of bandwidth from 2 c/s to 20 kc/s is analysed theoretically to show how the circuit may be modified to produce an integrator of bandwidth from 5 c/s to 2 Mc/s with less than 10% error at the band edges. The design and performance of the modified integrator is described in detail.

Employing a combination of well-known techniques an electrostatically compensated, null deflection electron beam probe technique has been developed capable of measuring electric field strengths varying from 1000 to 5 v cm^-1. The limitations of this technique are discussed.

Full experimental details are given of a probe which measures field strengths from 100 to 5 v cm^-1. This probe has been used to investigate the field distortion occuring during the transition from a Townsend to a glow discharge.

Equipment has been designed enabling temperatures from -150° C to 2200° C to be achieved inside the EM6 electron microscope with temperature control throughout the range. A low temperature stage cooled by liquid nitrogen and a medium temperature stage can each be calibrated by means of thermocouples and cover the temperature range -150° C to 800° C. A high temperature stage covers the range 800° C to 1200° C and a combination of the high temperature and cooling stages enables temperatures of at least 2200° C to be achieved. Temperatures above 800° C can be recorded by optical pyrometry at the specimen level with the aid of a metal mirror.

A liquid helium cooled finger has been fabricated to fit axially inside the standard Siemens cold finger. The apparatus has been used to examine a thinned copper transmission sample at a temperature below 29° K using a total liquid helium consumption of ten litres per hour. The temperature was determined by condensing Xe, Kr, Ar or N₂ on to the cold sample during observation.

Ferromagnetic domains can be detected by using the Kerr magneto-optic effect. The factors influencing the visibility of such domains on a microscopic scale are considered. An experiment is described which shows the dependence of the visibility on the numerical aperture of the condenser and the mean angle of incidence. The results are applied to the design of a magneto-optic microscope. The microscope performance is illustrated and resolution limitations indicated.

Details are given of the design of a photometer based on a stabilized power supply, bus headlamp bulb, selenium photocell and galvanometer. The testing and use of the instrument are described, with the precautions necessary to achieve accurate results. The instrument will measure optical densities from 0.1 to 1.4 with an accuracy better than 0.5%.

A portable spectro-radiometer is designed for the measurement of spectral irradiance in the visible region. It has an entrant system consisting of an integrating sphere with a conical baffle inside to obtain good cosine response. An interference filter of the wedge type is used as a dispersing element and narrow band (10 nm) energies are detected by a photovoltaic cell. The output is fed to a transistor amplifier and the current is calibrated for various wavelengths. The sensitivity at the wavelength of maximum response (570 nm) is 0.15 mw cm^-2 (10 nm)^-1 (1 μA)^-1.

A suggestion by Pike that it should be possible to use true focusing geometry in the X-ray diffractometer has been proved valid by the construction of such an attachment based on the design of the Seemann-Bohlin camera. A prototype model of this attachment for the Siemens diffractometer is described. With this attachment the diffractometer now measures only back reflection lines since the Bragg angle θ' is derived from the original 2theta angle recorded by the diffractometer, by the relation 2θ' = 90° + θ. Advantages of the true focusing technique are mentioned and an example, the 400 reflection from Mo, is shown using both curved and flat specimen geometry.

The instrument described measures small temperature changes. The sensitivity of the instrument varies with the ambient temperature, but this variation can be made as small as desired.

Attention is drawn to errors in evaluating the true pressure in the ultra-high vacuum region due to films deposited on the glass envelope of hot cathode ionization gauges.

A method of observing this effect is indicated. The origin of these films is briefly discussed. Chemical manipulations are described - in detail where necessary - for the removal of different types of films. An after-treatment is discussed to eliminate possible side-effects (secondary electron emission or photo-emission) due to the chemicals used.

Tests indicate satisfactory results for a number of gauges over a period of 18 months after using the methods described.

The object of this note is to describe a relatively simple way of constructing a thermistor thermometer with digital display. In principle a self-balancing servo-potentiometer is utilized to rotate a `Digidial' which indicates, in a digital manner, the angular position of the potentiometer shaft; in practice each digit represents 0.1 degc.

Nitrogen gas of essentially zero water content can be prepared very simply by electrically controlled boiling of liquid nitrogen. Particulars of the apparatus and its functioning are given.

A standard 10 μtorr vacuum evaporator was converted to the ultra-high vacuum range by installation of an ion-pumped, liquid nitrogen-cooled chamber within the standard vacuum chamber. Some advantages and disadvantages of this procedure are discussed.

A transistorized frequency doubling circuit for use in second harmonic phase-sensitive detection is described. The circuit will operate at frequencies up to 0.5 Mc/s. There is no lower frequency limit and no adjustment is necessary over the range 0.01 c/s to 0.5 Mc/s provided the amplitude of the input signal remains constant. A square-wave output signal is produced.