Patent Number: 054323533
Section: claims

1. A nuclear gauge for making measurements of traveling webs in continuous sheet-making processes, comprising: an enclosure means formed from a material having a high atomic number, including a unitary sidewall having an open aperture;  an encapsulated nuclear source of beta-radiation;  rotatable means mounted in the enclosure means for carrying the encapsulated nuclear source between two angularly-displaced positions relative to the sidewall; and  wherein the two angularly-displaced positions comprise a first position whereat the encapsulated nuclear source is positioned in generally radial alignment with the aperture and closely adjacent to a web that travels past the gauge for making measurements of the web, and a second position whereat the encapsulated nuclear source is positioned to face a sidewall of the enclosure means at a location remote from the first position. 2. A nuclear gauge according to claim 1 wherein the rotatable means includes a wheel-like member. 3. A nuclear gauge according to claim 2 wherein the enclosure means includes a cylindrical cavity and the wheel-like member is mounted on a rotary shaft for rotation within the cylindrical cavity. 4. A nuclear gauge according to claim 1 wherein the enclosure means is made from a material having a high atomic number. 5. A nuclear gauge according to claim 4 wherein the material having a high atomic number is a tungsten alloy. 6. A nuclear gauge according to claim 4 further including an aperture which is formed through the enclosure means to intersect the cylindrical cavity for providing a window through which the encapsuled nuclear source, when located in the first position, can emit radiation onto a web that travels past the window. 7. A nuclear gauge according to claim 4 wherein the outer diameter of the wheel-like member approximates the inside diameter of the cylindrical cavity so that, as the wheel-like member is rotated, the spacing between the periphery of the wheel-like member and the interior wall of the cylindrical cavity remains essentially constant. 8. A nuclear gauge according to claim 4 wherein the encapsuled nuclear source is connected to the wheel-like member by means of a cradle member that has an arcuate periphery of generally the same radius as the wheel-like member so that the overall cross-sectional profile of the wheel-like member, with the cradle member secured to it, is generally circular.