4.3.1.1 Ionization chambers

Ionization chambers are designed to operate at saturation current in the ion chamber region. The average current output is measured and is proportional to the amount of radiation to which the chamber has been exposed. Since the output is not dependent on the voltage, there is no need for a highly stable power supply. However, it is important that the voltage is steady enough to ensure that saturation current is maintained. The design of ionization chambers and the choice of filling gas depend on the particular application of the instrument.

In portable radiation monitoring instruments, the chamber is usually air-filled and constructed of low atomic number materials. If the instrument is to be used to measure alpha or beta radiation, the chamber must have thin walls or a thin end window. The only way that this type of detector can be used to discriminate between the types of radiation is by placing a shield over the thin end window to prevent the alphas or betas from entering the chamber.