COOLIDGE TUBE

Typical Number in Hospital:

Cost Bands:

References: 3

This is a stationary anode X-ray tube which was the fore-runner of the modern X-ray tube. It consists of an envelope, usually glass, in which there is a heated tungsten filament and focusing electrode from which electrons are attracted to a copper anode maintained at a high (kV) voltage, and into which is embedded a tungsten target. X-rays are produced when the electrons are stopped by the target. The efficiency of X-ray production is only about 1% and so there is the major problem of disposing of the remaining (heat) energy. Various designs of cooling mechanism are in use, some of which use oil cooling, since this also provides a good insulator for the very high voltages (up to 500 kV) which are required. To limit the voltage employed the cathode and anode are often maintained at equal negative and positive voltages.

Stationary anode tubes are now only found in small X-ray units (e.g. portable and dental).