Patent Number: 047956542
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the figures identical elements as well as elements of identical function are marked with identical reference numbers. In FIG. 1 a structure shielding the X-ray or gamma radiation arriving from the direction of arrow 7 comprises a protective layer 8 and a number of layers 11, 12, . . . 1n made of materials differing from each other, where n designates the number of the layers. The material of the first layer 11 from the direction of the arrow 7 shall be chosen according to the maximum energy of the incoming radiation in such a manner that the K-edge of the element of the layer 11 shall be lower than said maximum energy. Table I contains elements from which this element may be chosen in most practical cases. In the following, before the symbol of an element also the atomic number of the element will be given. In Table I there are the K-edge and L.sub.I -edge in the radiation absorption of each listed element, as well as the most probable .alpha.1 and .alpha.2 energy levels of a secondary radiation corresponding to the K-L electron shell transition of the excited element, all these in keV units. From the point of view of the practical application, the most important elements are 92U, 82Pb and 74W. When applying 92U, the radioactive radiation of 92U itself shall also be taken into consideration. The element of the second layer 12 shall be chosen so that its K-edge shall be in the energy range between the K-edge and L.sub.I -edge of the element of the first layer 11, as near as possible to the L.sub.I -edge. Table II contains elements being suitable for the layer 12 if the element of the layer 11 was chosen according to Table I. It can be seen that for the element 92U of the layer 11, in principle, any of the elements 50Sn, . . . 44Ru may be chosen because the K-edge of these latters is higher than the L.sub.I -edge of 92U. For any other elements 82Pb, . . . 73Ta of the layer 11, in principle, any of the elements 50Sn, . . . 41Nb may be chosen since even the K-edge of 41Nb is higher than the L.sub.I -edge of 82Pb. TABLE I ______________________________________ Element K-edge .alpha.1 .alpha.2 L.sub.I -edge ______________________________________ 92 U 115.6 98.4 94.6 21.7 82 Pb 88.0 75.0 72.8 15.9 79 Au 80.7 68.8 67.0 14.3 78 Pt 78.4 66.8 65.1 13.9 77 Ir 76.1 64.9 63.3 13.4 76 Os 73.9 63.0 61.5 13.0 75 Re 71.7 61.1 59.7 12.5 74 W 69.5 59.3 58.0 12.1 73 Ta 67.4 57.5 56.3 11.6 ______________________________________ TABLE II ______________________________________ Element K-edge .alpha.1 .alpha.2 L.sub.I -edge ______________________________________ 50 Sn 29.2 25.3 25.0 4.4 49 In 27.9 24.2 24.0 4.2 48 Cd 26.7 23.2 23.0 4.0 47 Ag 25.5 22.2 22.0 3.8 46 Pd 24.3 21.2 21.0 3.6 45 Rh 23.2 20.2 20.0 3.4 44 Ru 22.1 19.3 19.1 3.2 42 Mo 20.0 17.5 17.4 2.8 41 Nb 19.0 16.6 16.5 2.7 ______________________________________ The element of the third layer 13 shall be chosen so that its K-edge should be in the energy range between the K-edge and L.sub.I -edge of the element of the second layer 12, as near as possible to the L.sub.I -edge. Table III indicates elements and their K-edges which are suitable for the purpose of layer 13, if the element of the layer 12 was chosen according to Table II. TABLE III ______________________________________ Element K-edge ______________________________________ 30 Zn 9.7 29 Cu 9.0 28 Ni 8.3 27 Co 7.7 26 Fe 7.1 25 Mn 6.5 24 Cr 6.0 23 V 5.4 22 Ti 5.0 ______________________________________ It can be seen that for any one of the elements 50Sn, . . . 41Nb of the layer 12, in principle, any of the elements 30Zn, . . . 22Ti of Table III may be chosen, since even the K-edge of 22Ti is higher than the L.sub.I -edge of 50Sn. In respect of a practical application, the triple layer combination 82Pb - 50Sn or 48Cd - 29Cu or 28Ni and the combination 74W - 50Sn or 42Mo - 30Zn or 24Cr are advantageous. In several cases, the triple layer combination 82Pb - 50Sn - 29Cu is suitable and favourable as for its price. The structure according to the invention shall not necessarily be provided with a third layer 13 or further layers 13, . . . 1n. A double layer combination 82Pb - 50Sn or 48Cd or 42Mo may also be applied. For soft radiations /30-88 keV/, a double layer combination shall be applied expediently, where the element of the first layer 11 is 50Sn, that of the second layer 12 is 29Cu. FIG. 2 illustrates a structure where all layers 11, 12, . . . 1n are built up of thin layers. Accordingly, the layer 11 consists of thin layers 21, 22, . . . 2k of identical material, the layer 12 of thin layers 31, 32, . . . 3j of identical material, and the layer 1n of thin layers 41, 42, . . . 4i of identical material, all arranged on carrier 5. The carrier 5 is on the side of the thin layer package which is towards the radiation and it performs simultaneously the function of a protective layer. Between the thin layers of identical material thin separating layers not shown in FIG. 2 are foreseen, made e.g. of the oxide of the adjacent thin layer or of aluminium. The thin aluminium separating layers disperse the X-ray or gamma radiation and simultaneously increase thereby the shielding effect of the structure. For the sake of demonstration, none of FIGS. 2-4 is proportionate. In FIG. 3 the materials of the first thin layer 111, the second thin layer 121 and the third thin layer 131 are chosen according to the structure shown in FIG. 1. Thin layers 111, 121 and 131 form a layer group. In the structure m pieces of such layer groups are arranged one behind the other. The thin layers 111, 121, 131; 112, 122, 132; . . . 11m, 12m, 13m are arranged between two carriers 5 and 6. With this arrangement no separating layer must be placed between the thin layers since the adjacent thin layers are made everywhere of materials different from each other. In FIG. 4 such a structure is shown in which only the first layer 11 is built up of thin layers 21, 22, . . . 2k, the structure of the other layers 12, 13, . . . 1n is the same as in FIG. 1. The structure according to the invention may be shaped otherwise than a wall structure shown in the drawings. It may be manufactured e. g. as a flexible plate from which radiation protective clothing may be made or which may be used as a radiation protective casing having no flat surface.