Ionisation Chamber

• As the voltage is increased, the recombinations are decreased and the pulse height is increased.
• Once sufficient voltage is applied, all the primary ions are collected and hence the pulse height saturates.
• As the voltage in increased beyond a second threshold, the pulse height starts increasing again.
• This because of secondary ionisation created by the accelerating electrons moving towards the anode.
• This first plateau is called Ionisation Chamber Plateau.
• The voltage at which secondary ionisation begins is a characteristic of the gas, its pressure, the geometry of the detector, etc.
• The saturation current, being directly proportional to the amount of energy deposited, is a measure of the dose.
• Higher the energy deposited, larger is the saturation current.
• Technically, ionisation chamber can discriminate between alphas and betas.
• However, the currents are too feeble in this region.