Table of contents

The preparation of Geiger-Müller counters containing bromine as a quenching gas in a filling of neon and/or argon is described with particular attention paid to ensuring that the partial gas pressures are determined accurately. An empirical law relating the threshold voltage and the partial pressure of bromine is obtained. The true function of a small percentage of argon in a neon-bromine counter as regards its effect on the length of the plateau is considered.

Some new data appears on the oscillations produced by these counters.

A mechanical-electrical unit for the rapid systematic evaluation of functions of the type {sin, cos} 2πhx.{sin, cos}2πky.{sin, cos}2πlz is described.

The accuracy is of the order of 1% for hkl planes up to h = k = l = 20.

Experiments made in a periodically fluctuating wind current show that Sheppard and Meteorological office pattern cup anemometers over-estimate the mean wind velocity roughly in accordance with Schrenk's analysis except that the overestimation decreases somewhat more rapidly with increase of Schrenk's parameter K (defined in quation 2 below) than is indicated by the analysis. Changing the cup form from the hemispherical to the conical pattern (other characteristics being constant) results in only a slight decrease in the over-estimation error over a limited range of K.

A direct reading meter for the measurement of highly active samples of gamma emitting radioisotopes is described. It incorporates an ionization chamber and a d.c. amplifier. The source is placed within the chamber annulus and the operator is protected from it by 4 cm of lead. The instrument has been calibrated for a number of gamma emitting isotopes and samples ranging from 2 mg to over 2 000 mg radium equivalent may be quickly and safely measured.

A low temperature thermostat for the region - 20° C to - 78° C is described, which uses dry ice as refrigerant. A platinum resistance thermometer in conjunction with an electronic relay serves as a temperature sensitive element. The instrument is capable of maintaining any given temperature in the above range within an accuracy of ± 0.15° C for any desired time, with better regulation (± 0.05° C) over periods of hours.

The paper describes an improved form of construction for the lead assembly of Dickinson and Mueller type calorimetric resistance thermometers. The temperature lag of this assembly is much diminished on account of the reduced thickness permitted by the new design.

A Geiger counter spectrometer technique has been developed for the examination of the textures of small crystalline regions by a microbeam of X-rays. Both scanning and reflexion curve measurements are made. The spectrometer and counting equipment are described briefly, and some directional sensitivity properties of the counters are considered. The experimental procedure is discussed.

This paper summarizes the requirements of tripping circuits and spark gaps which enable a high-voltage impulse generator of one or more stages to be discharged in synchronism with the operation of such measuring equipment as a cathode-ray oscillograph or a rotating-mirror camera. A triggered spark-gap and the associated circuits which give accurate synchronism are described. A tripping pulse of only about 5 kV is required, and this may be obtained from the time sweep circuit of a high-voltage oscillograph, or from a blocking oscillator. Tripping of a single-stage generator is obtainable within 0.1 μsec of a pre-determined short delay time.

This instrument provides great flexibility for handling abnormal problems without loss of simplicity in normal operation. The oscillation angle can be adjusted to any value between 2° and 240°; the film records from 2θ = 4° to 170° with a camera of 2.75 cm radius; provision is made for fitting larger cameras and special accessories; the maximum inclination angle is 30°. The instrument may be used horizontally or vertically; its special features include a very compact demountable goniometer head of wide angular range and a simple device for setting the layerline screens accurately.