Beta Gage (Beta-ray Gage)
n Gage consisting of two facing elements, a β-ray-emitting source, and a β-ray detector. When a sheet material (e.g., plastic) is passed between the elements, some of the β-rays are absorbed, according to the area density or the thickness of the sheet. Signals from the detecting element can be used to control equipment that automatically regulates the thickness. The most usual sources are krypton 85 and strontium 90. Also used for particular applications are cesium 137, promethium 147, and ruthenium 106. See also Thickness Gauging.