Ionization Chamber - Principle, Working and Uses

 

IONIZATION CHAMBER

Principle -

The principle employed here is that charged subatomic particles can ionize gases. The number of ion-pairs produced gives us information not only on the nature of the incident’s particles but even on their energy.

Construction: -

The ionization chamber consists of a hollow metallic cylinder C, closed at both ends,

• There is a window W at an end for the entry of the ionizing particles or radiation.
• A metal rod R, well insulated from the cylinder, is mounted co-axially within the cylinder. R is connected to a quadrant electrometer E. A p.d. of several hundred volts is maintained be earthed guard ring G prevents leakage of charge from the cylinder to the rod.
• The chamber contains some gas like sulfur dioxide or methyl bromide.

Working: -

When a charged particle enters the chamber, it produces a large number of ion pairs in the enclosed gas, along its path.

• Positive ions move towards R and negative ions towards C.
• The quadrant electrometer E measures the rate of deposition of positive charges on R. The ionization currents are produced are quite small ≈ 10^-12 to 10^-15 amperes. Special electrometers and D.C. amplifying devices have to be employed to measure such small currents. 
• if individual particles are to be counted, then the pluses of current produced are fed to a pulse amplifier, which is joined to the ionization chamber by a coupling capacitor.

Uses: -

• Ionization chambers have been used to study α-particles, β-particles, protons, electrons, and nuclei of lighter elements.
• Ionization chambers were extensively used in the early studies of cosmic ray phenomena.
• It can also be used for measurements on X-rays and γ-rays.
• For neutron detection - the chamber is filled with boron tri fluoride vapor (where the boron is enriched with B10) or the chamber walls are lined inside with a boron compound in the form of a paste.