Patent Number: 
Section: description

FIG. 1 shows a cross section of a screen panel for converting X-rays into light photons according to the invention. The conversion screen panel comprises a first layer of composite material 1, a rigid foam plate that is transparent to X-rays 2, and a second layer of composite material 3. The circumference of the panel is reinforced with a framework 4. The rigid foam plate 2 and the layers of composite material 1 and 3 are assembled by gluing. The rigid foam used is a high density rigid foam such as, for example, the structural polymethacrylic foam marketed, for example, under the trade name xe2x80x9cROHACEL Foamxe2x80x9d and manufactured by the ROHM Company. The layers of composite material 1 and 3 are made out of, for example, a matrix of glass or carbon fibres set in resin. For a screen with dimensions, for example, equal to 45 cmxc3x9745 cm, the thickness of the foam plate may be equal to 7 mm and the thickness of the layers of carbon or glass fibres 1 and 3 may be equal to 0.5 mm. In a more general manner, the thickness of the foam plate may be more or less 2% of the length of the screen. The framework 4, preferably made out of the same material as layers 1 and 3, is particularly useful for strengthening the structure of large size screens. Alternatively, the foam plate may be replaced by a honeycomb plate made out of paper or plastic material, selected so that it only very slightly attenuates the X-rays. This type of honeycomb plate makes it possible to obtain the same mechanical characteristics as a rigid foam plate. The rigid foam plate is however preferred, since it attenuates X-rays less and is also more homogeneous to X-rays. FIG. 2 shows a screen for converting X-rays into light photons according to the invention. The screen comprises, apart from the panel represented in FIG. 1, a frame 5 deposited on the active face that ensures the conversion. The frame 5 is deposited around the circumference of the active face. The thickness of the frame 5 is more or less equal to the thickness of the active conversion layer 6. The presence of the frame 5 advantageously makes it possible to directly deposit the conversion layer on the panel. The technique for depositing the conversion layer also allows a simple manufacture of a high energy screen by the insertion of a sheet of tungsten between the panel and the conversion layer. Fastening elements (handles, fastening pick-ups) and electrical contacts (not shown in the figure) may be inserted into the frame 5. A conversion screen according to the invention is advantageously rigid, light and can be used in a vertical position, a horizontal position or in positions between the two. Such a screen can advantageously attain large dimensions. In addition, the thickness of the active layer 6 can easily be controlled when the layer is deposited. Adding intermediate layers between the panel and the active conversion layer, depending on the intended applications, is also easy.