Thorium Tungsten Wire

Many analytical and medical devices are using thorium tungsten wire as ion source. Why use thoriated tungsten materials?

Electrons are made available from a cathode in the source, which in most cases will use thermionic emission, i.e., heating the material so that electrons gain some energy and are able to escape the work function of the cathode material (the energy required per electron to leave the material). To lower work function, manufacturers would like to use thoriated tungsten wire.

Doping a tungsten wire with thorium can effectively improve the thermionic emission. Doping lowers the work function of the system, resulting in a thermionic current greater than the one produced from a pure W filament.