FIELD OF THE INVENTION

The present invention .refers to a laminar structure for influencing the effect of X-ray or gaπrna radiation on a target sensitive to the radiation which comprises at least two groups of layers wherein each group of layers emits a secondary radi¬ ation under the influence of the X-ray or gamma radiation or the secondary radiation of the previous layers. The structure proposed by the invention is capable of improving quality of a picture received by the means of the radiation and it can be applied also for securing protection of increased safety level against X-ray and gamma radiation.

BACKGROUND OF THE INVENTION

A method and a modifying body for influencing the effect of X-ray or gamma radiation on a target sensitive to the given kind of radiation and in particular for selective modification of a radiograph of an object is known from the U.S. Patent Do¬ cument 4764946 (granted to P. Teleki in August 1988), where¬ in the effect of the X-ray or gamma radiation is proposed to be influenced by the means of a structure comprising at least two layer groups intended to modify the energy spectrum of the radiation in order to ensure increased level of excitation in a substance sensitive to radiation, e.g. in an AgBr layer pre¬ pared for making X-ray radiographs. The layer groups include different metals, especially antimony (^Sb) and strontium

( ₃₈ Sr).

The method and modifying body disclosed in the mentioned ^■ U.S. patent specification offers a very simple solution for improving the conditions of preparing X-ray radiographs espe¬ cially in industrial applications. The metals forming the lay- er groups ensure a gradual energy transposition from one layer - to the other by excitation. In this method the energy transpo¬ sition is the basis of improving the quality of the received radiographs.

The reflection of the beams constituting X-ray or gaTina radiation is a problem difficult to solve. In the last decade the investigations have been directed to creating thin layer systems capable of applying in image forming processes. The known X-ray mirrors include a plurality of thin film layers, e.g. about 80 to 100 layers made alternatively of tungsten and carbon. The thickness of the layers in the systems which have become known is comparable with the wavelength of radiation applied. However, the level of the scattered radiation is re¬ latively high what results in the fact that the quality of the visible radiographs received is rather poor. In the radiology a further problem arises from the fact that both X-ray and gamma radiation require applying dif erent kinds of shield structures for securing protection of human beings and goods against radiation. The shields proposed ac¬ cording to the background art are relatively heavy and compli- cated, they consist of heavy structural elements.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a more ^" layer structure for influencing the effect of X-ray or gairma radiation, in particular for improving the quality of pictures received by the means of radiography and/or for increasing the safety level of means ensuring protection against the mention¬ ed kinds of radiation. The invention is based on the recognition that the thin

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layer structures can be applied for controlled scattering the radiation. This means, depending on the composition the ^' struc¬ ture can be applied for absorbing radiation and simultaneously or only for reflecting radiation in a manner which results in improved quality of the radiographs.

It is known that on the boundary surface consisted of layers built-up from ideal crystals the X-ray or gamma radia¬ tion is scattered. It is also known that the primary back- scatter phenomenon of extinction results in improved condi- tions of scattering and in absorbing radiation having relati¬ vely low energy. In a system comprising many reflecting layers the Co pton effect shows also changes in a series of interac¬ tions, the radiation becomes softer (its energy decreases) and this is advantageous in protecting systems. The intensive scattering process is also preferred in protecting structures having thickness excee ^' ding a minimal value because of ensuring a longer way for the propagation of the radiation in the mate¬ rial of the structure; this results in improved absorption conditions. The mechanism shown here can be influenced by dop- ing the material, by controlling the crystallization process thereof.

Hence, the invention refers to a laminar structure for influencing the effect of X-ray or gamma radiation on a target sensitive to the radiation which comprises at least one group of layers wherein the only one or- each group of layers emits a secondary radiation under the influence of the primary X-ray or gamma radiation or the secondary radiation of the previous layers. The essence of the invention is to provide a structure including the layers in at least one group, the layers being arrranged in a predetermined space sequence which can be sym¬ metric with regard to basic materials applied. The predetermi¬ nation means that the layers are arranged in the sequence of the atomic numbers of the elements constituting them, if a reflecting system is required. The layer system to be applied for reflecting X-ray or gamma radiation should consist of at

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least 32 layers with preferred thickness in the range from 0.0001 to 0.01 mm, wherein the value range from about 0.001 mm to about 0.002- m is especially advantageous.

The group of the layers should include at least one lay- er made of o^ (lead), _7^ W (tungsten) or _n -oTa (tantalum) and the further layers can be made from at least one of the fol¬ lowing metals: first group associated with oPb

^ (silver), _2Q CU (copper), ₂ g i (nickel), ^" .. O. (aluminium) second group associated with ₇ ¥ and ₇ Ta rp o (molybdenum), _Λ - _j Nb (niobium), r_- (vanadium) The elements of the first group are characterized with crys¬ talline lattice built-up according to the face-centered system (FCC) and those of the second group with lattice of body-cen¬ tered system (BCC). If the proposed structure is intended to ensure reflexion of X—ray or gamma radiation it is important to prepare the layers -with homogeneous distribution of their material having as low density- of dislocations and level of contamination as possible.

The structure proposed by the invention, if contaminated and includes dislocations may be applied also for increasing the safety level of protecting systems applied in an environ¬ ment of X-ray or ga ma radiation and this effect is increased by applying before the layers defined above and/or between two of them an iron based body made of iron including at least four of the following additives: .,-P, ^gS, po, -„Y and _ΛQ YΓ. Iron completed with the mentioned additives and the physical and chemical contamination of the crystalline lattice, i.e. the dislocations and the strange atoms ^" exert intensive scat¬ tering effect on X-ray or gairrna radiation entering the struc¬ ture and the scattered beams of radiation can be absorbed or reflected by the structure more intensively than the beams entering directly. The dislocations and the strange atoms constitute centers of the scattering process.

The proposed structure can be equipped with a protective layer arranged on the outer surface (on the first side striked by radiation), the protective layer being comprised of _Q CΓ or another substance showing high resistance against different corrosive and other dangerous factors.

The structure built-up according to the invention can be applied in the cosmic space and in normal gravity conditions. It constitutes a system of relatively low density which can be easily realized.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described in more detail on the basis of preferred embodiments and with reference to the attached drawings showing layers and layer systems not according to the real scale, for the sake of visibility. In the drawings

FIG. 1 is a schematical view of a two-layer basic em¬ bodiment of the structure proposed by the inven- tion, the structure advantageously being equipped with a scattering layer FIG. 2 is a schematical view of another basic embodiment of the structure proposed by the invention comp¬ rising more (e.g. ten) layers in a symmetric ar- rangement

FIG. 3 is a schematrical view of a preferred arrangement of the layers of the structure proposed by the invention, the structure beg divided into sub¬ systems of layers and FIG. 4 is a further schematical view of another preferr¬ ed arrangement of the layers constituting a rela¬ tively sophisticated part of a structure proposed by the invention.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

The structure for influencing the effect of X-ray or gamma radiation on a target sensitive to the radiation con- 5 sists of layers of equal or different thicknesses. The target arranged in the way of the reflected radiation produced by the structure proposed by the invention from primary radiation R is not shown in the drawings. The target can be a film being sensitive to X-ray or gaπ_ma radiation or a screen or any

10 image-sensing means, e.g. Nal or Csl crystal detector doped by Tl. The structure of the invention can be applied also, if the components allow to do so, for preparing a screen or shield protecting the environment against the X-ray or gamma radia¬ tion.

15 The structure of the invention is consisted of a basic layer 1 and at least a second layer 3 (Fig. 1). The basic layer 1 is made of oPb or ₇ J or ₇ -**Ta and the second layer 3 consists of any one of _Λ *-*Ag, qCu, po i or ..-Al (metals associated generally with o Pb), _^ p o, _Λ ^ b or p„ (associated

20 with „.W and _7o Ta). The basic layer 1 is arranged either as the first in the way of radiation R after a scattering layer 2 (Fig. 1) and/or a covering layer 4 which will be described la ter or in the middle part of a symnetric layer system. - . The basic layer 1 is followed (Fig. 1) or preceded and

25 followed (Fig. 2) by the second layer 3 and if necessary, by third, fourth and fifth layers 5, 7, 9 consisting of the othe elements listed up above. The elements are arranged always in a sequence according to their increasing (structure as shown in Fig. 2) or decreasing (structure as shown in Fig. 1) atomi

30 numbers given in the above lists, too. In a more layer system the second layer may be consisted of ₇ -_ _> Ta, too.

According to the invention the basic and further layers 1 _. 3, 5, 7, 9 of a reflecting system are made of metals crys¬ tallizing in the face-centered crystalline lattice (FCC) and/

35 /or in the body-centered crystalline lattice (BCC), characte-

rized with only one lattice constant. The elements are the following:

TABLE 1.

In the structures comprising more layers than five the arrangement is built-up from symmetric pieces including the basic layer(s) 1 in the middle part (Fig. 3 and 4). The number of the layers is advantageously at least thirty-two, between two layers it is preferred to prepare separating layers 6 con¬ sisted of an appropriate oxide, having thickness not exceeding about 0.0001 mm. The invention renders possible to create material sys¬ tems showing double effect. If the layers 1, 3, 5, 7, 9 con¬ sist of a substance characterized by crystalline disorder, re¬ latively high density of dislocations and/or prepared with selected alloying components or additives, they cause inten- sive scattering effect with backscatter phenomenon, i.e. scat¬ tering effect acting backwards practically without any remark¬ able order. The dislocations, the surface of the grains com¬ prising the strange atoms consitute the centers of scattering. It is therefore advantageous to apply such layers 1, 3, 5, 7, 9 together with those prepared of pure material having low density of dislocations which act together as an active system reflecting the radiation.

The scattering (protecting) layers 2 can include also the metals listed above. It is also advantageous to apply iron ^26*^ ^e ^ ~^ ^or ^* ^e ^ ^asic πiaterial of a such layer, wherein iron

comprises at least four of the following alloying components, additives and elements: ~gY, _Λ QZΓ, p ₇ Co, _. __ , ,,-S. The thick¬ ness of the scattering layer 2 is not limited, however, it is proposed to prepare it with thickness lower than that of the 5 basic and further layers 1, 3, 5, 7, 9 of a reflecting system. Because of high thermal resistivity, the scattering layer 2 can be applied for covering X-ray tubes.

The scattering layer 2 is arranged either on the surface of the structure directed to the source of radiation R or in

10 its depth, between two layers 1, 3, 5, 7, 9 of a reflecting system.

The outer surface of the structure can be made with a covering layer 4 consisted of any material of required charac¬ teristics, e.g. of p _Λ r which is advantageous because of

15 excellent heat and light reflecting features, high corrosion resistivit , etc.

The basic and further layers 1, 3, 5, 7, 9 of reflecting capability are arranged in a sequence following that of the atomic numbers, because this is very advantageous with regard

20 to the absorption processes: the characteristic radiation is absorbed in the adjacent metal layer. The radiation scattered and backscattered by the basic and further layers 1, 3, 5, 7, 9 is also intensively absorbed by the structure if the basic layer 1 is arranged in the middle part and the second and fur-

25 ther layers 3, 5, 7, 9 constitute in both directions a symmet¬ ric system. The other and preferred possibility is to arrange the basic layer 1 consisted of the first metal in the FCC or BCC group (see Table 1.) or of ₇ ~Ta as first to receive the primary radiation. - 30 It is especially preferred to prepare the structure from at least three metals, e.g. in the following arrangements gi¬ ven only by way of example and, for the sake of simplicity, . without the atomic numbers:

Pb, Ag,- Al, Al, Ag, Pb, Ag, Al Pb, Cu, Al, Al, Cu, Pb, Cu, Al W, Mo, V, V, Mo, W, Mo, V W, Nb, V, V, Nb, W, Nb, V Ta, Mo, V, V, Mo, Ta, Mo, V ^'

Pb, Mo, V, V, Mo, Pb, Mc, V W, Cu, Al, Al, Cu, W, Cu, Al

Of course, other arrangements can be selected, too. The scattering layer 2 is generally applied between the source of the radiation R and the basic and further layers 1 , 3, 5, 7, 9 of the reflecting system, it consists of iron and the additives mentioned above. Of course, the normal contami¬ nating elements of iron, as silicon or carbon, etc. are always present, they can not be exluded.

The structure of the invention preferably consists of thirty-two layers, consisting of two- and three-component sub¬ systems. The examples of the last are given above. Some examples of the two-components systems: Pb, Al, Al, Pb, Al W, Al, Al, ¥, Al Ta, V, V, Ta, V etc.

It is also preferred to apply a high heat and corrosion resistance layer made of e.g. ^Cr between the two- and ore- -layer subsystems.

The basic and further layers 1, 3, 5, 7, 9 of the structure proposed by the invention have thickness in the range from 0.0001 to 0.002 mm, however, the lower and higher values in the range from 0.0001 to 0.01 mm or more may be also selected, if required.

The scattering layer 2 can be thicker than the basic and further layers 1, 3, 5, 7, 9, but generally it should be not thicker than the reflecting system built-up with the basic and further layers 1, 3, 5, 7, 9. The structure realized according to the present inven-

tion results in remarkable improvement of the quality of ra¬ diographs, i.e. pictures registered by the radiologic means. It can simultaneously constitute a high effectivity shield se¬ curing protection against X-ray and gamma radiation showing high resistivity against chemical substances and thermal ef¬ fects. The shield can be produced in form of plate-like ele¬ ments of high elasticity, too.

The layers can generally be made by known techniques of preparing thin layers, e.g. by vapour deposition, however, the thicker layers can be prepared by rolling and united by the means of an adhesive and/or the oxide layers.

The main advantage of the proposed structure is the pos¬ sibility of double use.