Similar in construction and operation to an [[ionization chamber]]. Usually the proportional counter is a metal chamber. filled with gas, with a central electrode maintained at a positive voltage with respect to the shell. The voltage level of the central electrode is related to the critical voltage value where gas amplification begins. The proportional counter is operated in that limited voltage range where the charge flow across the counter is proportional to the primary [[ionization]].

In well logging, it is designed for the detection of neutrons. A gas is used which is suitable for the production of ionizing particles upon reaction with incident neutrons. The gas commonly used is He<sup>3</sup> but may be BF<sub>3</sub>. The BF<sub>3</sub> gas, maintained at about 1 atmosphere, requires a voltage level of 2400-2500 volts and produces a larger pulse than that in He<sup>3</sup>; but, the He<sup>3</sup> maintained at higher pressure and operating at about 1300 volts is more efficient in the detection of neutrons. Compare [[ionization chamber]], [[Geiger Mueller counter|Geiger-Mueller counter]], and [[scintillation counter]].