In addition, they can be used to verify package contents and parts presence or position. Gauges employ either transmission or backscatter techniques. X-ray, gamma, or beta sources are used, depending upon the nature of the application.
Beta gauges are appropriate for relatively low mass materials such as paper, plastic and films.
These materials provide low attenuation to X-ray or gammas, which renders transmission devices unsuitable. Backscatter gauges are used when only one side of the process has convenient access. Radiation from a source is also subject to backscatter from interaction with matter. For instance, beta particles can enter one surface of a material and be deflected back at a large angle after partial energy deposition. The amount of backscatter is dependent upon atomic number and thickness.