Patent Number: 051130785
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to a transparent radiation shielding structure which may be used for, for example, a work face of a glove box that is designed to handle radioactive substances safely. We will hereinafter discuss a work face of a glove box for handling radioactive substances in nuclear facilities as a prior art that is related to the present invention. However, it should be noted that the application of the present invention is not necessarily limited thereto and that the invention maybe generally applied to radiation shielding structures that are required to be transparent. Referring to FIG. 2, a conventional glove box 21 has a work face 22, which is formed with glove ports 23 having gloves (not shown) attached thereto and passing therethrough, and a worker, using the gloves, handles a radioactive substance in the box. The work face 22 of the glove box 21 must be capable of shielding radiation and also transparent so that the worker can view the inside of the box 21. In addition, the work face 22 must have a satisfactorily airtight structure. The conventional work face 22 has a double-panel structure comprising an airtight panel 24 made of a transparent acrylate resin material and a radiation shielding panel 25 of a transparent lead acrylic resin material (or lead glass) that is disposed outside the airtight panel 24, as shown in FIG. 3. The airtight panel 24 is brought into contact with a panel mounting portion 27 through a gasket 26 for airtight seal that is fitted to the outer peripheral edge of the panel 24. In addition, a retaining plate 29 is pierced with a plurality of bolts 28 that are provided on the panel mounting portion 27, and the airtight panel 24 is fastened with a nut 30 through the retaining plate 29, thereby securing the airtight panel 24 to the panel mounting portion 27. The transparent radiation shielding panel 25 is disposed outside the airtight panel 24 to shield radioactive rays, e.g., neutron beams, gamma rays, etc., by lead that is contained in the radiation shielding panel 25. The reason why the prior art adopts the double-panel structure comprising the airtight panel 24 and the radiation shielding panel 25 is that, if the radiation shielding panel 25 is attached directly to the panel mounting portion 27 through the gasket 26, which is fitted to the outer peripheral edge of the panel 25, to form a single-panel structure, lead that is contained in the radiation shielding panel 25 is oxidized by chemicals, e.g., nitric acid, in the box 21 to form an oxide film on the panel surface, resulting in the panel 25 becoming opaque, so that it becomes difficult to view the inside of the box 21. The above-described prior art suffers, however, from the problems stated below. Since a gap 31 is present between the airtight panel 24 and the radiation shielding panel 25, which constitute a double-panel structure, the opposing surfaces 24a and 25a of the two panels 24 and 25 become cloudy with moisture or are stained with suspended dust, resulting in a lowering in the transparency. In addition, radiation cannot be shielded at the edge of the gap 31 between the airtight panel 24 and the radiation shielding panel 25, so that radioactive rays leak therethrough. Further, since two panels 24 and 25 need to be mounted, the assembly operation efficiency is low. SUMMARY OF THE INVENTION It is a first object of the present invention to provide a radiation shielding structure which is designed so that it is possible to shield radiation by a single panel and still prevent lowering in the transparency due to oxidation, thereby eliminating the problem of lowering in the transparency due to the gap between two panels of the conventional double-panel structure and the problem of the leakage of radioactive rays from the peripheral edge of the gap between the two panels, and thus improving the efficiency of the panel mounting operation. It is a second object of the present invention to provide a radiation shielding structure which is designed so that it is possible to mount the panel stably in the single-panel radiation shielding structure. It is a third object of the present invention to provide a radiation shielding structure which is designed so that it is possible to prevent the panel from being damaged by a retaining plate that holds the outer peripheral edge of the panel in the single-panel radiation shielding structure. It is a fourth object of the present invention to provide a radiation shielding structure which is designed so that it is possible to prevent displacement of a gasket in the single-panel radiation shielding structure. It is a fifth object of the present invention to provide a radiation shielding structure which is designed so that it is possible to improve the airtightness in the single-panel radiation shielding structure. To attain the above-described objects, the present invention provides a radiation shielding structure which comprises a lead transparent plate and a nonlead transparent plate which is laminated on at least one side of the lead transparent plate. Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification. The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.