1. The Borough Polytechnic, London, S.E.1.

Abstract

WE have investigated the characteristics of Geiger–Müller counters containing mixtures of argon with small quantities of xenon (0–7 per cent), oxygen (0–0.5 per cent) and nitrogen ( 1 per cent), to total pressures of 700 mm. mercury. That counters filled with this mixture would behave as 'fast' counters in a manner similar to organically quenched counters was first reported by Shore¹, although Riedel² reported that using the filling recommended by Shore produced no Geiger region. Using counters of the conventional 'gamma' type, glass bodies with cylindrical cathodes of various materials together with a 4.7 megohm series resistor and a linear amplifier of a gain of about 25, we find that optimum proportions of the gas mixture to produce the best plateaux are : xenon (3.5 per cent), oxygen (0.3 per cent), nitrogen (1.2 per cent), with argon added to give a total pressure of 700 mm. mercury. Such a mixture gave a plateau about 170 V. in length, with a starting voltage of 1,460 V. and a plateau slope of 0.02 per cent/V.