English: plot of electric field strength in the region of the proportional counter anode. The diagram visualises the strength of the electric field in the vicinity of the anode of a co-axial gaseous radiation detector. As the anode is approached the electric field strength increases exponentially, so that within a short distance from the anode it is sufficient to generate Townsend elecron avalanches if a free electron enters the region. The gas proportional detector is designed so that this region occupies only a small volume adjacent to the anode so that most of the gas space is present only to act as an ion chamber to allow interaction of incident radiation. A Geiger-Muller tube exhibits the same characteristic of increase in field strength at the anode, but a higher voltage is applied than for a proportional counter with the same geometry, which results in a larger region where Townsend avalanches can be created, and higher field strengths are encountered which gives rise to the generation of UV photons, and thereby multiple avalanches. The Townsend avalanche region in the G-M tube may occupy all or most of the gas space.