ABSTRACT
Proportional counters are operated in region III of the pulse height curve for gas detectors. In this region an electronic pulse produced by ions moving through the detector is proportional to the original energy absorbed in the detector gas by a radiation particle, be they charged particles, neutrons, gamma rays or x rays. Various gas mixtures are often introduced into the detector chamber to improve performance. Gas additives and mixtures can improve electron velocities, improve avalanche gain, decrease the required operating voltage, improve energy resolution, and eliminate spurious pulses. Quench gases are usually chosen with ionization potentials below that of the host gas, a precaution that allows charge to transfer from the host gas to the quench gas while rendering the reverse process improbable. Quench gases should also be electronegative so they are not prone to electron attachment. Electron collisions in a gas can leave a gas in an excited state, which generally de-excites by the emission of a photon.
