A Toroidal Geiger Counter

Abstract

A TOROIDAL Geiger counter has been constructed in an attempt to produce a γ-ray sensitivity detector with a response independent of the position of the γ-ray source over a small region of space. The counter was made from two U-shaped half-sections (radius ½ in.), one of which is shown in the photograph, pressed from 24 S.W.G. oxygen-free copper. The counter was designed in the first instance for experiments in which it was necessary to pass the counter freely over the human head, and for this reason a toroid of mean diameter 12 in. was made. The centre wire, of 0.008-in. diameter tungsten, was supported by eight equi-spaced ‘Perspex’ disks with central holes through which the wire was a push-fit. These insulators were keyed to one half-section of the counter by phosphor-bronze spigots which projected $\frac{1}{8}$ in. into the edges of the disks. The connexion to the centre wire was taken out through a metal-to-glass seal of commercial pattern, and the two halves of the counter were soldered together using solder-paste and 60/40 soft solder. No difficulty was found in making a vacuum-tight joint without excessive penetration of flux into the tube. A connexion to the vacuum system was made via a lead alloy stem, and the tubes were pumped and filled with a mixture of 10 per cent ethyl alcohol and 90 per cent argon to a pressure of 10 cm. mercury in the usual manner.