Patent Number: 047956542
Section: summary

BACKGROUND OF THE INVENTION The subject matter of the invention is a structure for shielding X-ray and gamma radiation. Usually, wall structures made of a metal of high absorption, such as of lead, are used for shielding X-ray or gamma radiation. The thickness of the wall structure is chosen according to the required attenuation of the radiation. The drawback of such known structures is their relatively great weight. The invention relates to a structure in which various materials are combined in laminated construction. SUMMARY OF THE INVENTION Hence, the invention is a structure for shielding X-ray and gamma radiation, which is of laminated construction having at least n layers made of materials different from each other, where n is greater than or equal to two, and each of the first n-1 layers comprises an element converting at least a part of the X-ray or gamma radiation to be shielded or of the secondary radiation emitted by the preceding layer, respectively, into an X-ray or gamma radiation, the energy of which is greater than the energy level defined by the K-edge of the next layer. According to an embodiment of the invention, the element of the first layer shall be chosen so that its K-edge should be lower than the maximum energy of the X-ray or gamma radiation to be shielded, whereas the element of the second layer --and in the case of n being higher than two each of the further layers--so that its K-edge should be between the K-edge and the L-edge of the element of the preceding layer, advantageously in the vicinity of this L-edge. The invention can be advantageously made in such a way that the number of the different layers should be two or three. The first layer may comprise uranium, lead, gold, platinum, iridium, osmium, rhenium, tungsten and/or tantalum, whereas the second layer may comprise tin, indidm, cadmium, silver, palladium, rhodium, ruthenium, molybdenum and/or niobium. If there is a third layer, it may comprise zinc, copper, nickel, cobalt, iron, manganese, chromium, vanadium and/or titanium. As a practical matter, a triple layer combination may be advantageous, where the first layer comprises lead or tungsten, the second layer comprises tin, cadmium or molybdenum, whereas the third layer comprises zinc, copper, nickel, iron or chromium. It is especially favourable if the first layer comprises lead, the second one tin and the third one copper. A double layer combination may often suffice where the first layer comprises lead, and the second layer comprises tin, cadmium or molybdenum. In the case of a radiation of lower energy, a double layer combination may be adequate, where the first layer comprises tin and the second one copper. It is highly advantageous if the structure according to the invention is built up of thin layers for increasing the absorption effect. This may occur in such a manner that one or more layers consist of thin layers of identical material between which thin separating layers are arranged. The separating layers may be made of an oxide of the adjacent thin layer or of aluminium, the latter improves the absorption properties of the structure as a layer dispersing the X-ray or gamma radiation. The thin-layer structure according to the invention may also be achieved in such a manner that it comprises a number of layer groups arranged one after the other, each comprising n thin layers of materials different from each other. In this case no thin separating layers are necessary. The aluminium thin layers dispersing the X-ray or gamma radiation, however, are advantageous even here. They may be arranged, e.g. as per layer groups or as per several layer groups. In the structure according to the invention, built up at least partly of thin layers, the thickness of the thin layers is less than 150 .mu.m, preferably less than 50 .mu.m. In the case of a definite thickness of the whole structure the absorption increases by the reduction of the thickness of the thin layers, i.e. by the increase of the number of thin layers, thus, a thin layer thickness of 0.1-20 .mu.m is especially advantageous. The thin layers arranged in the structure according to the invention need not have by all means the same thickness. The beneficial effect of the thin layers in the structure according to the invention is based presumably on the fact that the barriers at the boundary surfaces of the thin layers are considerably higher than the barriers in the inside of the thin layers, therefore, the thin layers act as boundary surfaces for moving charged particles. Consequently, the thin layers damp the electrons generated both by the Compton-effect and the photoeffect. In the structure according to the invention the thin layers can be applied to one side of a carrier, advantageously of a copper plate or chromium steel plate protecting against the external effects, arranged on a side of the thin layers which is towards the radiation to be shielded. However, the thin layers may be arranged between two carriers. The thin layers produced, e.g. by rolling can be fastened to each other and to one or two carriers by gluing or pressing. The thin layers may be applied to the carrier by vacuum evaporation, too. The advantage of the structure according to the invention consists in that a required protection against radiation can be achieved by lower weight and thickness. The structure can be used in each field of the radiation protection. It may be applied e.g. as a casing of an X-ray tube, as a wall or clothing protecting against radiation, and as a radiation shielding of instruments or experimental equipment. It may be produced in rigid or even in flexible form.