Divide a curve:
This curve can be divided within six parts and forms the basis of three categories of detectors that differ in the magnitude of voltage applied. These are:
- Ionization chamber,
- Proportional counter and
- Geiger-Muller counters.
Each of these is suitable for specific applications. In order to understand the characteristic features of the curve in Figure, let us assume that after applying voltage V1 a single particle of radiation enters the detector through its window and produces a certain number of primary ion-pairs (call it n). During this process all the energy of the particle is lost. If the voltage applied is smaller than V1 only a fraction of these ion pairs will reach the electrodes and the remainder will undergo ion recombination. The region of V = 0 to V1 is often called the region of ion- recombination and is of no use in the detection of radiation. However, if the applied voltage is increased further (V>V1) number of ion-pairs formed do not increase significantly but remain somewhat state. In other words, for voltages between V1 and V2 number of ion-pairs formed remains almost the same and no secondary ion-pairs are produced. In voltage region V1 to V2, ion current remains independent of applied voltage but directly proportional to the energy of radiation dissipated in the detector. This region is used for ionization chamber detector. Such detectors are often used for counting α and β- particles. These were found very useful in early stages of development.