Gaseous Detectors

All gaseous detectors signal the passage of charged particles by gathering the electrons from the ion pairs produced in the gas, usually after some amplification. The history of the gas detectors starts with the counter described by Rutherford and Geiger in 1908 [1]. It consisted of a cylindrical metallic tube filled with air or other simple gases at some 5 Torr and with a 0.45 mm diameter wire along its axis. The negative high voltage on the tube with respect to the wire was adjusted to below the discharge limit. With a gas gain of a few 103, only α-particles could be detected as current pulses with an electrometer. This counter was the first electronic counter, following the optical counting of light flashes in the study of radioactive substances with scintillating crystals. A major step was taken when Geiger found that by replacing the anode wire by a needle with a fine pin, electrons could also be detected [2]. These needle counters became the main particle counter for years. Already in 1924, Greinacher started using electronic tubes to amplify the signals [3].