SHIELDING FACILITY FOR X-RAYS OR gamma -RAYS

Abstract: A shielding facility serves to prevent x-rays or gamma -rays which are generated by, for example, irradiation of electron beam from leaking out of an opening through a shield passage. The shielding facility includes a shielding wall (2) defining therein a shield passage (3) having an inlet opening and an outlet opening. The shielding wall (2) is adapted to accommodate a source (1) which generates x-rays or gamma -rays. The shielding facility further includes a plurality of partition walls (7-1, 7-2 and 7-3) disposed in the shield passage (3). The partition walls (7-1, 7-2 and 7-3) are bent at least one time between the inlet opening and the outlet opening of the shield passage (3).

Description: DESCRIPTION SHIELDING FACILITY FOR X-RAYS OR γ-RAYS Technical Field The present invention relates to a shielding facility for X-rays or γ-rays, and more particularly to a shielding facility forpreventingX-rays orγ-rayswhicharegeneratedby, for example, irradiationof electronbeamfromleakingoutof anopeningthrough a shield passage. Background Art In order to shield X-rays orγ-rays radiated froma radiation source, it has heretofore been customary to employ a shielding facilitywhich surrounds the sourcebyshieldingwalls ofconcrete, lead, or iron forthereby attenuating the radiatedX-rays orγ-rays as they pass through the shielding walls and preventing them from leaking out. However, in the case where substance or material is brought into and out of the shielding facility, the interior of the shielding facility is ventilated, or access to the interior of the shielding facility is required, the shielding facilitymust have an opening. Therefore, the radiation source cannot fully be sealed. As an example of the above case, there is a case in which the radiation source is included in a production line, material to be irradiated by the radiation source is brought into the interior of the shielding facility, and products processed by the radiation source are taken out of an opening of the shielding facility, or a case in which flue gases or waste water are introduced intothe interiorofthe shielding facility, irradiated by the radiation source, and then taken out of the shielding facility, or a case in which flue gases or waste water are introduced into a process vessel in the shielding facility, irradiated with electron beam, and then taken out of the shielding facility. Particularly, in case of irradiation of electron beam, the secondaryX-rays are generatedwhenthe electronbeamcollides with the target gas or the like, thus the process vessel, and the flue gases or waste water which are irradiated with the electron beam become a radiation source of X-rays. In such cases, it is necessary to employ some structure for shielding X-rays or γ- rays so as not to leak through the opening. Generally, X-rays or γ-rays, which are among electromagnetic waves, are attenuated when they pass through a substance, becomeweaker as the distance fromthe radiation source increases, and are attenuated each time they are reflected by a surface of a substance. Therefore, in order to prevent X-rays or γ-rays from leaking through an opening, it has been customary to surround a passage from the radiation source to the opening by shielding walls that are highly resistant to the leakage of X-rays or γ-rays, increase the length of the passage, and bend the passage. In the specification, the passage which is surrounded by the shielding walls that are highly resistant to the leakage of X-rays or γ-rays is defined as "shield passage". FIG. 14A of the accompanying drawings shows a known shielding facility. The shielding facility in FIG.14A has outer shielding walls 22 defining a central chamber which houses a radiation source 21 generating X-rays or γ-rays. One of the walls 22 has an opening 26 covered with a large door 27. The opening 26 is mainly used for access to the interior of the shielding facility. However, since the door is required to have a shielding capability substantially equal to the shielding wall to prevent X-rays or γ-rays from transmitting the door and leaking out of the door, the door becomes expensive. Further, since the door can be opened only when X-rays or γ-rays are not generated, this type of the shielding facility cannot be used in a case where substance or material is brought into and out of the shielding facility while X-rays or γ-rays are being generated, or a case where the shielding facility is ventilated. FIG. 14B of the accompanying drawings shows a known shielding facility having a bent shield passage surrounded by shielding walls. The shielding facility has outer shielding walls 22 defining a chamber which houses a radiation source 21 generating X-rays or γ-rays. The shielding walls 22 define thereina tortuous shieldpassage 23 whichextends fromthechamber to an opening 28 defined in oneof the shieldingwalls 22 and closed by a door 29. The door 26 is an ordinary door, and when X-rays or γ-rays are not generated, the door can be opened and access to the interior of the shielding facility can be effected through the shield passage by opening the door. Further, by leaving the dooropen, the interioroftheshielding facilitycanbeventilated while X-rays or γ-rays are being generated. FIG. 15 of the accompanying drawings shows another known shielding facility having a bent shield passage surrounded by shieldingwalls. Shieldpassages 23Aand 23B are defined by outer shielding walls 22, and a central chamber in the shielding walls 22 houses a radiationsource 21whichgenerates andradiates X-rays or γ-rays. The shield passages 23A and 23B also have openings 24 and 25 defined, respectively, in opposite ends thereof. While X-rays or γ-rays are being generated, substance or material is brought into the interior of shielding passage through the shield passage 23A, and is brought out of the interior of the shielding passage through the shield passage 23B. When X-rays or γ-rays travel through a shield passage, they areattenuateddependingonthedistancewhichtheyhavetraversed, i.e. , the length of the shield passage, and reflections which they have been subjected to. If the intensity of the x-rays or γ- rays at the outlet of the shield passage is 1/100 of the intensity of the X-rays or γ-rays at the inlet of the shield passage, then the attenuation ratio for the X-rays or γ-rays is expressed as 100. For calculating the attenuation ratio, an empirical equation (1), given below, is used, and shield passages are designed using the equation (1). I = I 0 x L -2 x R _N • • • (1) where I 0 is the intensity of X-rays or γ-rays at points which are unit length distant from the center of a radiation source, I is the intensity of X-rays orγ-rays at an outlet openingof the shield passage, L is the distance from the center of the radiation source to the outlet opening, R is the attenuation ratio per reflection of the X-rays or γ-rays, and N is the number of times that the X-rays or γ-rays have been reflected over the distance from the source to the outlet opening. Therefore, the attenuation ratio η for the X-rays or γ-rays at the opening is proportional to the square of the distance (L) from the radiation source and also proportional to the Nth power of the number of reflections. That is, the attenuation factor η is given by the following equation. η = L 2 x R N • • • (2) Since the attenuation ratio η for X-rays or γ-rays is dependent on the distance and the number of reflections as indicated by the above equation (2), a shielding facility having a shield passage with an opening needs to have a larger space and a more material for shielding X-rays or γ-rays than a shielding facility which is fully enclosed. This can readily be understood from a comparison between FIGS. 15A and 15B. As X-rays or γ- rays are produced in a greater quantity and have a higher energy, a greater distance and a larger number of reflections for attenuation are required, and hence a larger space and a more material for shielding are required. If the amount of substance or material brought into and out of the shielding facility increases, then the cross-sectional area of the shield passage also increases, resulting in an increase inthe space and shielding material. Particularly, in case of the flue gas treating process in which flue gases are irradiated with electron beam in the shielding facility, since the amount of flue gases to be treated is extremely large, an area of the shield passage ranges several m 2 to several 10 m 2 . The increased space imposes a limitation on the layout of the shielding facility, and the increased shielding material increases the cost of the shielding facility and the weight of the shielding facility, resulting in an increase in the cost of a foundationon which the shielding facility is installed. Disclosure of Invention It is thereforeanobjectof thepresent inventiontoprovide a shielding facility for X-rays or γ-rays which can greatly reduce a space and material for a shield passage defined therein. In order to achieve the above object, according to a first aspect of the present invention, there is provided a shielding facility for X-rays or γ-rays, comprising: a shielding wall defining therein at least one shield passage including an inlet opening and an outlet opening, the shielding wall being adapted to accommodate a source which generates X-rays or γ-rays and is positioned at the side of the inlet opening of the shield passage; and at least one inner plate or wall disposed in at least part of said shield passage, said inner plate or wall extending in the direction from said inlet opening to said outlet opening of said shield passage and being bent at least one time in said shield passage. The inner plate or wall may be arranged in the shield passage such that the outlet opening of the shield passage is visually concealed from the inlet opening of the shield passage. The inner plate or wall may comprise a division plate or partition wall by which the shield passage is divided into a plurality of passageways. The division plate or partition wall may be in the form of a folding screen having at least one fold. The inner plate or wall may comprise a spiral plate or wall. X-rays or γ-rays may be generated by irradiation of electron beam. The electron beam may be used to treat flue gas. According to a second aspect of the present invention, there is provided a shielding facility for X-rays orγ-rays, comprising: a shielding wall defining therein at least one shield passage including an inlet opening and an outlet opening, the shielding wall being adapted to accommodate a source which generates X- rays or γ-rays and is positioned at the side of the inlet opening of the shield passage, the shield passage being of a bent configuration; and at least one division plate or partition wall disposed inat least part ofthe shieldpassageto divide the shield passage into a plurality of passageways. The division plate or partition wall may have a thickness which is substantially at least one-twentieth andatmost tentimes the half-value layer of a material of the division plate or partition wall. Heretofore, it has been considered that according to the design procedure used to design a shielding facility based on the above equation (1), the attenuation ratio for X-rays or γ-rays does not change even if the shield passage is divided because the distance from the source and the number of reflections remain unchanged. However, the inventors of this application have found that the attenuation ratio for X-rays or γ-rays can be increased if the shield passage is divided into a plurality of passageways by a division plate or partition wall. It has also been confirmed that the attenuation ratio is increased even if the division plate or partition wall has a thickness which is not large enough to shield X-rays or γ-rays by itself. Brief Description of Drawings FIG. 1 is a horizontal cross-sectional view of a shielding facility for X-rays or γ-rays according to a first embodiment of a first aspect of the present invention; FIG. 2 is an enlarged perspective view of division plates or partition walls of the shielding facility for X-rays or γ- rays according to the first embodiment of the first aspect of the present invention; FIG. 3 is a horizontal cross-sectional view of a shielding facility for X-rays or γ-rays according to a second embodiment of the first aspect of the present invention; FIG. 4 is a graph showing X-ray attenuation ratios with respect to thickness vs. half-value layer ratios; FIG. 5 is a graph showing X-ray attenuation ratios with respect to the numbers of units of division plates or partition walls; FIG. 6 is a horizontal cross-sectional view of a shield passage which is used to explain the equation (2) and (3) hereinafter; FIG. 7 is a schematic view showing an example in which a shield facility for X-rays and γ-rays of the present invention is applied to an electron beam gas treatment system; FIG. 8 is a perspective view of a shielding facility for X-rays or γ-rays which has a shield passage divided by division plates or partition walls according to an embodiment of a second aspect of the present invention; FIG. 9 is a horizontal cross-sectional view of an example of a shielding facility; FIG. 10 is a fragmentary vertical cross-sectional view of the example shown in FIG. 9; FIG. 11 is a graph showing X-ray attenuation ratios with respect to thickness vs. half-value layer ratios; FIG. 12 is a graph showing X-ray attenuation ratios with respect to L 2 /S; FIG. 13 is an enlarged perspective view of division plates or partition walls of the shielding facility for X-rays or γ- rays according to an embodiment of a combination of the first and second aspects of the present invention; FIG. 14A is a horizontal cross-sectional view of a conventional shielding facility for X-rays or γ-rays; FIG. 14B is a horizontal cross-sectional view of another conventional shielding facility for X-rays or γ-rays; and FIG. 15 is a horizontal cross-sectional view of still another conventional shielding facility for X-rays or γ-rays. Best Mode for Carrying Out the Invention Embodiments of the first aspect of the present invention will bedescribed below indetail with reference to FIGS.1 through 6. FIG. 1 shows a shielding facility for X-rays or γ-rays according to a first embodiment of the first aspect of the present invention. As shown in FIG. 1, the shielding facility houses a radiation source 1 such as substance or material irradiated by electron beam which radiates secondary X-rays, and has outer shielding walls 2 defining a shield passage 3 therein. The shieldingwalls 2 accommodate units 4-1 and 4-2 of division plates or partition walls therein. The shielding passage 3 has an inlet A for X-rays positioned at an end thereof adjacent to the source 1 and an outlet B for X-rays positioned at an opposite end thereof remote from the source 1. The outlet B is normally closed by a shielding door 2d. The units 4-1 and 4-2 of division plates or partition walls are arranged in the shield passage 3 such that the inlet A is visually concealed from the outlet B. FIG.2 shows in an enlarged scale each of the units 4-1 and 4-2 of division plates or partition walls. As shown in FIG. 2, each unit comprises an upper panel 5, a lower panel 6 spaced downwardly from the upper panel 5, and a plurality of division plates or vertical partition walls 7-1, 7-2 and 7-3 extending between the upper and lower panels 5 and 6 and horizontally spaced inadirectionperpendiculartothe longitudinal axis of the shield passage 3 (see FIG. 1). The shielding walls 2 contact closely the upper panel 5 andthe lower panel 6 so that X-rays areprevented from leaking out of the contacting portions of the shielding walls 2, and the upper and lower panels 5 and 6. The division plate or partition wall 7-1, 7-2 or 7-3 constitutes an inner plate or wall, and divides the shield passage 3 into a plurality of laterally juxtaposed passageways as shown in FIG.2. Each of the division plates or partition walls 7-1, 7-2 and 7-3 is in the form of a folding screen and is of a 90°-bent shape with a central vertical fold line extending between its upper and lower ends that are fixed respectively to the upper and lower panels 5 and 6. Although each of the division plates or partition walls 7-1, 7-2 and 7-3 has only one fold 7f in FIG. 2, it may have one or more folds. FIG. 3 shows a shielding facility for X-rays or γ-rays according to a second embodiment of the present invention. In the second embodiment of FIG. 3, the shielding facility has a spiral partition wall 8 disposed in the shield passage 3 and extending between the inlet A and the outlet B. The partition wall 8 is coiling around a center line C L extending in a longitudinal direction of the shield passage 3 in a constantly changing series of planes. Other details of the shielding facility shown in FIG. 3 is identical to those of the shielding facility shown in FIG. 1. Those parts and components in FIG. 3 which are structurally and functionally identical to those shown in FIG. 1 are denoted at the same reference numerals. An experiment was conducted on the shielding facility shown in FIG. 1 as described below. In the experiment, two of the unit of division plates or partition walls shown in FIG. 2 were placed in the shielding facility as shown in FIG.1, and an X-ray shield test was conducted on the shielding facility to shield secondary X-rays generated by electron beam irradiation. In the X-ray shield test, X-rays were emitted from the irradiated material at maximum energies of 0.5 MeV and 0.8 MeV. The partition walls were made of various materials including iron and lead, and had different thicknesses as shown in Table 1 below. Thickness vs. half-value layer ratios in Table 1 is defined as the ratios of the thicknesses of the partition walls to the half-value layers shown in Table 2, and the half-value layer is defined as the thickness of a sheet of material which reduces the intensity of X-rays passing through it to one-half its initial value, and depends on the kind of the material and the maximum energy of the X-ray. Table 1 (Partition walls used in the experiment) Material for Thickness of Thickness vs. partition partition half-value layer ratio wall wall (mm) 0.5 MeV 0.8 MeV 1 0.10 0.08 Iron 3 0.29 0.23 10 0.95 0.76 20 1.91 1.52 10 2.49 1.42 Lead 20 4.97 2.83 40 9.95 5.67 Table 2 (Half-value layer with respect to X-rays) Material for partition wall X-ray energy Half-value layer (Density) (MeV) (mm) Concrete 0.5 34.2 (2.4) 0.8 42.3 Iron 0.5 10.5 (7.86) 0.8 13.2 Lead 0.5 4.0 (11.34) 0.8 7.1 The total absorption coefficients of the materials used in the calculation of the half-value layers were cited from "Radiation" published by Kyoritsu Shuppan, and the densities of the materials were cited from "Rika Nenpyo" (Scientific Almanac) published by Maruzen. If it is assumed that X-ray intensities at the inlet A and the outlet B of the shield passage are represented by I A and I B , respectively, then an attenuation ratio η of the shielding facility is indicated by η = I A /I B' FIG.4 shows X-ray attenuation ratios with respect to thickness vs. half-value layer ratios which weremeasured for different materials and thicknesses of division plates or the partition walls, and different applied X-ray energies. It was confirmed from FIG. 4 that any transmitted X-raysweresuppressed ifthepartitionwalls had athicknesswhich was 2.5 times (at an attenuation ratio of 2 2-5 = 5.7) the half-value layer. It was also confirmed that even if the partition walls had a thickness whichwas less than 2.5 times the half-value layer, a larger attenuation effect was achieved than the case in which no partition wall was employed. For example, even in the thickness vs. half-value layer ratio of 0.1, the attenuation ratio ranging from 50 to 100 was obtained, which shows a large attenuation effect. Increases in the thickness of the partition walls do not vary the attenuation effect, but make the shielding facilitymoredisadvantageous interms ofthe installationprocess or economical considerations. Practically, therefore, the thickness of the partition walls may be at most several tens times the half-value layer. InanotherX-rayshieldtest, thenumberofunits ofdivision plates or partition walls was increased (an additional unit of division plates or partition walls was included as indicated by the broken lines in FIG. 1), but the thickness of the partition walls was not varied. X-rays were generated fromthe X-ray source 1 at a maximum energy of 0.5 MeV, the partition walls of lead had a thickness of 20 mm, and attenuation ratios for the respective first, second, and third units of division plates or partition walls were measured. The results are shown in FIG.5. Since the partition walls of lead had a thickness of 20 mm, only an attenuation effect on reflected X-rays which are not influenced by transmitted X-rays is shown in FIG. 5. It was confirmed that the relationship between the number of units of division plates or partition walls and the attenuation ratio satisfied not the above equation (1), but the following equation (3) which the inventors of this application have found. I = I„. ι [(α x L B 2 /S n ) + β] '1 ■ • • (3) The above equation (3) will be described below. If it is assumed that, as shown in FIG. 6, the intensities of X-rays from a radiation source 1 at respective bends P x , P 2 , • • • , P„ of a shield passage 3 defined by outer shielding walls 2 are represented by I lf I 2 , • • , I n , respectively, then the X-ray intensity I n at the bend P n can be calculated from the X-ray intensity l n _. at the preceding bend P-,^ according to the above equation (3), where S n is the cross-sectional area of the shield passage from the bend P n _ 1 to the bend P n , L n is the distance from the bend P.,^ to the bend P n , and and β are constants depending on the cross-sectional shape of the shield passage. In the equation (3), [(α x L n 2 /S n ) + β] indicates the attenuation ratio per bend. The equation (3) shows that the attenuation ratio at a bend of the shield passage is proportional to the square of the distance from a reflecting point and inversely proportional to the cross-sectional area of the shield passage. It follows, therefore, that the attenuation effect of the shield passage can be increased by reducing the cross-sectional area of the shield passage due to, for example, reduction of the pitch of the partitionwalls, aswell as by increasingthe number of reflections and the distance. The shielding facility shown in FIG. 3 was also subjected to an X-ray shield test by irradiation of electron beam. The spiral partition wall was made of iron and had a thickness of 10 mm. X-rays were generated from the X-ray source 1 at maximum energies of 0.5 MeV and 0.8 MeV. In the X-ray shield test, an X-ray attenuation ratio η (= I A /I B ) was 2000 at 0.5 MeV and 1500 at 0.8 MeV. Therefore, the shielding facility shown in FIG. 3 produced the same attenuation effect as the shielding facility shown in FIG. 1. Sincethe shielding facility forX-rays orγ-rays according to the first aspect of the present invention has division plates or partition walls disposed in the shield passage, the shield efficiency of the shielding facility with respect to X-rays or γ-rays is increased, and an installation space for the shielding facility and a construction cost of the shielding facility can be reduced greatly. FIG. 7 shows an example in which a shield facility for X-rays and γ-rays of the present invention is applied to an electron beam gas treatment system. The gas to be treated is introduced from an inlet duct 31 into a process vessel 32 in which the gas is irradiated with electron beam whose energy is in the range of several 10 keV to several MeV, from an electron beam generator 33. After irradiation of electron beam, the gas is discharged froman outlet duct 34. The secondary X-rays whose maximum energy is equal to the energy of the electron beam are generated when the electron beam collides with the target gas. Therefore, the shielding facility for X-rays is installed so that the shielding walls 2 surround the process vessel 32, the inlet duct 31, and the outlet duct 34 to prevent the leakage of the secondary X-rays. In order to prevent the leakage of the secondary X-rays fromopenings of the inletduct 31 andtheoutlet duct 33, the partition walls 7-1, 7-2 and 7-3 having a plurality of folds are provided in the inlet and outlet ducts 31 and 33 such that inlet openings 31A and 32A for X-rays are visually concealed from outlet openings 31B and 32B for X-rays, respectively. The partition walls 7-1, 7-2 and 7-3 are formed by a shielding material made of concrete, iron or lead, and the thicknesses of them are in the range of several one-tenth to several tens of the half-value layer of the shielding material. The thickness of the partition wall is determined on the basis of the shieldingmaterial and the maximum energy of the generated X-rays. The electron beam generator 33 is a self-shielding type in which the generated X-rays are prevented from leaking out of a penetration 37 by itself. Next, an embodiment of the second aspect of the present invention will be described below with reference to FIGS. 8 through 12 . FIG. 8 shows in perspective a shielding facility for X- rays or γ-rays according to an embodiment of the second aspect of the present invention. As shown in FIG. 8, the shielding facility includes a shield passage having an inlet 11 for X-rays or γ-rays and an outlet 12 for X-rays or γ-rays, and defined by outer shielding walls 13. The shield passage is bent at an angle of 90°. The inlet 11 and the outlet 12 are positioned, respectively, at opposite ends of the shield passage. The shielding facility also has division plates or partition walls 14 disposed in the shield passage. The division plates or partitionwalls 14 includevertical andhorizontaldivisionplates orpartitionwallswhicharecombinedtogethertodivide theshield passage into a plurality of parallel passageways 18 each having a rectangular cross section. As described above, the above equation (3) shows that the attenuation ratio at a bend of the shield passage is proportional to the squareof thedistance froma reflectingpoint and inversely proportional to the cross-sectional area of the shield passage. It follows, therefore, that the attenuation effect of the shield passage can be increased by reducing the cross-sectional area of the shield passage as well as by increasing the number of reflections and the distance. For example, if the partition walls 14 divide the shield passage into nine equal parallel passageways 18, as shown in FIG. 8, thenthe attenuation effect per bend is about nine times greater than the attenuation effect which would be achieved without the partition walls 14. Therefore, if the shield passage has five bends and is divided into nine equal parallel passageways, then the attenuation effect of this case is about 60,000 (= 9 5 ) times greater, although the volume of the shield passage remains substantiallyunchanged. Itwas experimentallyrevealedthatthe above attenuation effect was obtained when the thickness of each of the partition walls 14 was at least about one-twentieth (1/20) of the half-value layer with respect to X-rays or γ-rays passing through the partition walls 14. Consequently, the partition walls 14 may be of a very small thickness. This is another important fact which has been found by the inventors of this application. An experiment was conducted on the shielding facility according to the present invention as described below. FIG. 9 shows an X-ray shielding facility having outer shielding walls 13 which define therein a shield passage with an X-ray source (substance or material irradiated by electron beam) 15 positioned therein. As shown in FIG. 10, a partition wall 14 was placed in a region 16 (shown hatched in FIG. 9) of the shield passage parallel to the floor of the shield passage. In FIG. 9, a reference numeral 17 represents an outlet opening. The shield passage had a width of 900 mm and a height of 3,000 mm, and the partition wall 14 was spaced 1,000 mm upwardly from the floor to divide the shield passage into two passageways 18 whose cross-sectional areas had a ratio of 2 : 1. X-rays were generated from the X-ray source 15 at maximum energies of 0.5 MeV and 0.8 MeV. The partition wall 14 was made of various materials including aluminum, iron and lead, and had different thicknesses as shown in Table 3 below. Thickness vs. half-value layer ratios in Table 3 mean the ratios of the thicknesses of the partition walls to the half-value layers shown in Table 4. Table 3 (Partition walls used in the experiment) Material for Thickness of Thickness vs. partition partition half-value layer ratio wall wall (mm) 0.5 Me 0.8 MeV aluminum 5 0.16 0.13 10 0.33 0.27 1 0.10 0.08 Iron 3 0.29 0.23 10 0.95 0.76 20 1.91 1.52 10 2.49 1.42 Lead 20 4.97 2.83 40 9.95 5.67 Table 4 (Half-value layer with respect to X-rays) Material for Partition wall X-ray energy Half-value layer (Density) (MeV) (mm) Concrete 0.5 34.2 (2.4) 0.8 42.3 Aluminum 0.5 30.5 (2.69) 0.8 37.7 Iron 0.5 10.5 (7.86) 0.8 13.2 Lead 0.5 4.0 (11.34) 0.8 7.1 The total absorption coefficients of the materials used in the calculation of the half-value layers were cited from "Radiation" published by Kyoritsu Shuppan, and the densities of the materials were cited from "Rika Nenpyo" (Scientific Almanac) published by Maruzen. X-ray intensities I 1 and I 3 (see FIG. 9) at the inlet and outlet ofthe shieldpassageweremeasured, and attenuationratios η (= Iχ/1 } ) were calculated to compare attenuation effects of the shield passage according to the present invention and a shield passage with no partition wall. FIG. 11 shows X-ray attenuation ratios with respect to thickness vs. half-value layer ratios. In FIG. 11, the point (a) represents X-ray attenuation ratios with respect to half-value layers for the shield passage (having a cross-sectional area of 2.7 m 2 ) with no partition wall, O represents X-ray attenuation ratios with respect to half-value layers for the upper passageway (having a cross-sectional area of 1.8 m 2 ) in the shield passage withthe partitionwall, andΔrepresents X-ray attenuation ratios with respect to half-value layers forthe lower passageway (having a cross-sectional area of 0.9 m 2 ) in the shield passage with the partition wall. A review of FIG. 11 shows that the attenuation ratio is larger as the cross-sectional area is smaller at the same distance fromthe X-ray source and the same number of reflections, and that the attenuation effect increases when the shield passage is divided by the partition wall. FIG. 12 shows X-ray attenuation ratios (Ij/I.) measured for one reflection intheshieldpassage shown in FIG.9. The equation (3) described above can be derived from the data shown in FIG. 12. It was confirmed from FIG. 11 that the attenuation effect does not change even when the thickness of the partition wall is reduced to one-tenth of the half-value layer (the partition wall of iron having a thickness of 1 mm with respect to the maximum X-ray energy of 0.5 MeV). When the thickness of the partition wall is reduced to 0.08 times the half-value layer (the partition wall of iron having a thickness of 1 mmwith respect to the maximum X-ray energy of 0.8 MeV), the attenuation effect is slightly lowered, but it is still effective in increasing the attenuation efficiency without varying the shape of the shield passage. Further increases in the thickness of the partition wall do not vary the attenuation effect, but make the shielding facility more disadvantageous interms ofthe installationprocess oreconomical considerations. Practically, therefore, the thickness of the partitionwallmay be atmost about ten times the half-value layer. According to the second aspect of the present invention, since the shielding facility for X-rays or γ-rays has the shield passage divided by division plates or partition walls, the shield efficiency of the shielding facility with respect to X-rays or γ-rays is increased, and the shielding facility needs a relatively small installation space and can be constructed relatively inexpensively. Next, an embodiment of a combination of the first and second aspects of the present invention will be described below with reference to FIG. 13. The combination of the first and second aspects of the present invention provide a great effect for attenuation of X-rays and γ-rays. FIG. 13 shows in an enlarged scale a unit 4-1 (or 4-2) of division plates or partition walls, and corresponds to FIG. 2. The unit 4-1 (or 4-2) shown in FIG. 13 is identical to the unit 4-1 (or 4-2) shown in FIG. 2 except that it incorporates a plurality of division plates or partition walls 9 extending between the partition wall 7-1 and the partition wall 7-3 and vertically spaced in a longitudinal direction of the shield passage 3 (see FIG. 1). This division plate or partition wall 9 constitutes a second partitionwall. That is, as shown in FIG. 13, the shielding passage 3 (see FIG. 1) is divided into a plurality of laterally juxtaposed passageways by the division plate or partitionwall 7-1, 7-2 or 7-3, and the above passageway is divided into a plurality of vertically juxtaposed subpassageways each having a rectangular cross section by the division plate or partition wall 9. As a result, X-ray attenuation ratio can be further promoted. Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims. Industrial Applicability The present invention is suitable for a shielding facility inwhich a radiation sourceradiatingX-rays orγ-rays cannot fully be sealed because substance ormaterial is required to be brought into and out of the facility while X-rays or γ-rays are being generated from the source. The present invention is preferably applicable to a flue gas treatment system in which X-rays are generatedwhen electron beamcollides with flue gas to be treated and the treated gas or byproduct is required to be discharged from an opening of a shield passage.

Claims: CLAIMS 1. A shielding facility for X-rays or γ-rays, comprising: a shielding wall defining therein at least one shield passage including an inlet opening and an outlet opening, said shielding wall being adapted to accommodate a source which generates X-rays or γ-rays and is positioned at the side of said inlet opening of said shield passage; and at least one inner plate or wall disposed in at least part of said shield passage, said inner plate or wall extending in the direction from said inlet opening to said outlet opening of said shield passage and being bent at least one time in said shield passage. 2. A shielding facility according to claim 1, wherein said inner plate or wall is arranged in said shield passage such that said outlet opening is visually concealed from said inlet opening. 3. A shield facility according to claim 1, wherein said inner plate or wall comprises a division plate or partition wall by which said shield passage is divided into a plurality of passageways. 4. A shielding facility according to claim 3, wherein said division plate or partition wall is in the form of a folding screen having at least one fold. 5. A shielding facility according to claim 3, further comprising at least one second division plate or partition wall disposed in at least part of said shield passage to divide said passageway into a plurality of subpassageways. 6. A shielding facility according to claim 1, wherein said inner plate or wall comprises a spiral plate or wall. 7. A shielding facility according to claim 1, wherein said X-rays or γ-rays are generated by irradiation of electron beam. 8. A shielding facility according to claim 7, wherein said electron beam is used to treat flue gas. 9. A shielding facility for X-rays or γ-rays, comprising: a shielding wall defining therein at least one shield passage including an inlet opening and an outlet opening, said shielding wall being adapted to accommodate a source which generates X-rays or γ-rays and is positioned at the side of said inlet opening of said shield passage, said shield passage being of a bent configuration; and at least one division plate or partition wall disposed in at least part of said shield passage to divide said shield passage into a plurality of passageways. 10. A shielding facility according to claim 9, wherein said X-rays or γ-rays are generated by irradiation of electron beam. 11. A shielding facility according to claim 10, wherein said electron beam is used to treat flue gas. 12. A shielding facility according to claim 9, wherein said division plate or partition wall has a thickness which is substantially at least one-twentieth of the half-value layer of a material of said division plate or partition wall.

Inventors: IIZUKA YOSHITAKA, IZUTSU MASAHIRO, IIZUKA, YOSHITAKA, IZUTSU, MASAHIRO
Applicants: EBARA CORP, IIZUKA YOSHITAKA, IZUTSU MASAHIRO, EBARA CORPORATION, IIZUKA, YOSHITAKA, IZUTSU, MASAHIRO
Application year: 1997
Main classification: G21F7
IPC codes: G21F7