The use of radiation in devices used to gauge (measure or monitor) certain activities is probably one of the widest uses in industry. These devices, which can be portable or set in a fixed position, can monitor the flow of liquids; can measure and control the thickness of metals, films, paper, and plastic; and can monitor material density. Some gauging devices are also used to determine the content of materials as in the case of a moisture-density gauge that is often used to determine the water content of soil. These types of devices generally contain radioactive materials that are gamma-ray or neutron emitters.
There are other devices used for measurement that are not gauges. These might include an x-ray fluorescence analyzer to determine the makeup or content of an item or something like a gas chromatograph used for quality control to assure the correct mixture or purity of a substance.