Plates of the ionization chamber:

In common, a 1 MeV beta particle will eject around 50 electrons per centimeter of travel, although a 0.05 MeV beta particle will eject around 300 electrons.  A lower energy beta ejects more electrons since it has more collisions.  Every electron generates through the beta particle, therefore traveling by air, will generates thousands of electrons.  The current of 1 micro-ampere consists of about 10¹² electrons per second.

If 1 volt is applied to the plates of the ionization chamber displays in next figure a few of the free electrons will be attracted to the positive plate of the detector. This attraction is not strong since 1 volt does not create a strong electric field among the two plates.  A free electron will tend to drift toward the positive plate, causing a current to flow that is denoted on the ammeter. All of the free electrons will not make it to the positive plate since the positively charged atoms which resulted while an electron was ejected might recapture other free electrons. Thus, the ammeter will register only a fraction of the number of free electrons among the plates.