Impact ionization

In the impact ionization in the original meaning electrons are " knocked out " by incident, sufficiently fast electrons from atoms or molecules and these ionized by it. In a broader sense, you can call it that each ionization good (ie, for example, when the photoelectric effect) carried out by any collision process and not by the action of an electric field or by other means.

In the impact ionization can occur under certain circumstances to an avalanche effect, that is, the liberated electron can in turn release more than another new electron. This current-amplifying effect may be desirable ( Geiger counter ) or undesirable. Especially when he goes so far that an electron radiation from outside is necessary only at the beginning and the current flow is then automatically maintains ( independent gas discharge ), it can be destructive.

Examples

• Fluorescent tube
• Geiger counter
• Flash
• Avalanche breakdown in a diode