General Comments about Construction of Gas-Filled Detectors

9 GENERAL COMMENTS ABOUT CONSTRUCTION OF GAS-FILLED DETECTORS 

This section summarizes the important characteristics of gas counters. 

Geometry. Parallel-plate counters are almost exclusively ionization chambers. The intense fields needed for gas multiplication can be produced only in cylindrical or spherical geometry. 

Gases and pressures used. For ionization chambers, almost any gas or pressure may be used. Even atmospheric air has been used. 

As discussed in Sec. 5.6.1, the quenching gas in a GM counter is either an organic polyatomic molecule such as ethyl alcohol, or a halogen such as bromine or chlorine. A typical mixture is 0.1 percent chlorine in neon. The gas pressure in a GM counter is, in most cases, less than 1 atm. The pressure affects the operating voltage. 

---