Introduction
This topic covers how electric current passes through gases, which are normally insulators; the small ions that gases contain, called aeroions, and their effect on living organisms; and ozone therapy, which uses ozone generated by an electric discharge. It links the physics of ionisation and discharge with the biological action of charged particles and oxidising gases.
Electric current in gases
A gas is an insulator at low field because its molecules are electrically neutral. A current can flow only if free charge carriers are created. The process is ionisation, the removal of an electron from a molecule, which leaves a positive ion and a free electron. The sources of ionisation are ionising radiation (X-rays, gamma rays, alpha and beta particles), ultraviolet light, cosmic rays, high temperature in a flame, and strong electric fields.
- Non-self-sustained discharge: the current exists only while the external ionising source acts, and it saturates when all the produced ions reach the electrodes.
- Self-sustained discharge: at high field the free electrons gain enough energy to ionise new molecules, so the discharge continues without an external source. The forms are the glow discharge, the corona discharge at points and sharp edges, the spark, and the arc.