Plot of relative level of ion-pair current with increasing voltage applied between anode and cathode for a wire cylinder ionisation detection system with constant incident ionising radiation. This covers the practical areas of operation of the Geiger-Muller counter, the proportional counter and the ionisation chamber. Alpha particles are more ionising than beta particles, so more current is produced in the ion chamber region by alpha than beta, but the particles cannot be differentiated. More current is produced in the proportional counting region by alpha particles than beta, but by the nature of proportional counting it is possible to differentiate alpha and beta pulses. In the Geiger region, there is no differentiation of alpha and beta as any single ionisation event in the gas results in the same current output. Note that gamma and X-ray photons result in the same plot shape; current also being dependent on radiation energy