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Abstract:

Two methods are described. (1) Low-voltage radiography. (2) Electron emission radiography. For low-voltage radiography an x-ray tube with a beryllium window must be used, and 4 to 7 kilovolts is recommended. The film cannot be used in its paper envelope because this would register its own image. The bare film is placed, emulsion side up, in a vacuum register board with the paper to be examined on top of it. Over these is laid a thin sheet of cellulose acetate. Exposure is made through this thin sheet. Loading and exposure must be carried out in complete darkness. The successful radiograph should show the structure of the paper in good contrast. The film used is either Kodak Industrial X-ray film or Kodak Contrast Process Ortho film. For electron emission radiography high-voltage x-rays (200-250 kilovolts) are used. These do not themselves register the image on the film, but cause electrons to be given off from metals in contact with the film. The image is made by the electrons thus emitted. For the radiography of paper the high-energy x-rays strike a sheet of lead. The lead emits electrons uniformly, which are partly absorbed by the paper. Those that pass through the paper register on the film. All three layers, lead, paper, and film must be in very close contact and therefore a vacuum cassette is used. The film is the same as for low-voltage radiography. If metallic pigments are present as a design on the paper, these will give an image in low-voltage radiography, but not in electron emission radiography.