Fluke Biomedical 440RF - Manual (Page 25)

Theory of Operation
General
3
3-1
Section 3
Theory of Operation
3.1 General
When the ion chamber is exposed to radiation, the internal air volume becomes ionized. A DC potential
applied between the outer shell and center electrode separates the newly formed ion pairs before they
can recombine, and collects them.
The ions, upon reaching the electrodes are restored to neutral gas atoms, through the process of taking
on (or giving up) electrons. This causes a DC current flow in the external circuit.
The ion chamber can be considered a constant current generator whose output current is directly
proportional to the rate of internal air ionization (or exposure rate). However, these currents are
extremely small and special electrometer circuitry is required to measure them.