Patent Application
20090108216
The present invention relates generally to a shield for high-energy radiation and more specifically to a relocatable radiation shield for radiation used for inspection of freight containers.
Freight containers are used to consolidate cargo items into standardized logistical units for rapid and economical transfer from one form of transport to another. Millions of freight containers are in transit annually, and a large port may process thousands of containers every day. The standardization of containers and container handling and transport equipment has been very successful in improving efficiency and reducing cost, leading to shipment in freight containers of more than ninety per cent of the world's non-bulk cargo.
The contents of freight containers may be inspected for safety, security, or tariff reasons. Generally, only a small fraction of shipments arriving in freight containers at a port or freight terminal are inspected due to logistical limitations. For example, a common type of freight container known as an isotainer has a width dimension of approximately 8 feet (2.4 meters), a height dimension of approximately 8 feet 6 inches (2.6 meters), and one of five standard lengths ranging from approximately 20 feet (6.1 meters) to 53 feet (16.2 meters), although other dimensions are sometimes used. Such a large enclosed volume may hold many thousands of small items, contain some cargo hidden behind or underneath other cargo, or be filled with cargo that is fragile, heavy, toxic, or susceptible to shifting within the container. Unpacking, inspecting, and repacking a container may require the efforts of a dozen or more inspection and freight personnel for ten hours or more. It is well understood within the shipping industry that inspecting the contents of every container by such methods would increase shipping costs and cause unacceptable shipping delays.
Automated scanning systems employing high-energy radiation are sometimes used to inspect sealed freight containers and improve the ability of customs and security agencies to detect hazardous or illegal cargo. Some automated scanners direct X-rays, neutrons, gamma rays, or other forms of radiation from one or more emitters through a freight container to one or more detectors to create an image representing the contents of the container. The image is examined and compared to the freight container's stated manifest. Images of dangerous items, images that are difficult to interpret, or differences between objects visible in an image and the manifest may cause the container to be selected for additional inspection procedures.
Radiation having sufficient energy to penetrate the walls of a freight container and reveal information about the container's contents may be strong enough to be a health hazard to personnel working near an automated scanner. Nearby mechanical, electrical, and electronic systems may also be at risk of malfunction or damage from exposure to radiation from an automated scanner. It is therefore desirable to isolate personnel and equipment from the harmful effects of the radiation.
Several methods of isolating people and equipment from radiation used in automated scanners are known. Some scanners have a metal enclosure surrounding an object to be scanned for absorbing most of the radiation used for scanning. Such scanners, of which an airport luggage scanner is an example, have sufficient shielding to protect personnel and equipment working in close proximity to the scanner. However, the high cost of the scanner's shielding enclosure generally limits such scanners to the examination of relatively small objects. Furthermore, it may be impractical to adapt an existing scanner installation to new types of radiation emitters and detectors or to increase the energy emitted within the scanner to form images of dense targets.
Scanners for large objects such as vehicles or freight containers are sometimes placed inside permanent buildings or between fixed walls to attenuate radiation used in scanning to safe levels. Providing space for fixed structures may be very difficult in crowded terminal areas. Also, the initial cost for a dedicated structure is high, as are the costs for modifying or relocating an existing structure to accommodate changes in preferred logistical flow.
Personnel and equipment may be protected from radiation used in scanning by providing an intervening separation distance between the scanning equipment and personnel work areas. The separation distance comprises a safety zone which personnel are not to enter and in which equipment susceptible to damage or malfunction from radiation is not to be placed during operation of the scanning equipment. The size of the safety zone is proportional to the energy density used for scanning an object. As with permanent shielding structures, finding space for an adequately large safety zone is sometimes impractical, and the size and location of a safety zone may have undesirable effects on logistical flow in a terminal area.
What is needed is a means of shielding radiation from an automatic scanner that is relatively fast and economical to place in operation, safe to use in relatively small areas, relocatable by logistical equipment commonly used in terminal areas and freight yards, adaptable for scanning relatively large or dense objects, adaptable to changes in preferred logistical flow in a terminal area, and adaptable to a variety of automated scanning equipment.
The present invention comprises a relocatable radiation shield for radiation used for inspection of freight containers. The relocatable radiation shield comprises at least one layer of solid shielding material. A layer of the relocatable radiation shield is adapted to contain a shielding fluid. For embodiments comprising more than one layer of shielding material, different layers may optionally have different shielding properties. A layer of solid shielding material in combination with a layer adapted to contain a shielding fluid has a combined shielding property effective for selectively shielding X-rays, gamma rays, electromagnetic interference (EMI), radio frequency interference (RFI), high energy neutrons, electrons, protons, alpha particles, beta particles, or other forms of radiation, or combinations of more than one form of radiation. A selected shielding property may correspond to a thickness of a shielding layer, a composition of a shielding layer, a number of shielding layers, a shape of a shielding layer, or a combination of these attributes.
A layer of solid shielding material in combination with a layer adapted to contain a shielding fluid, which may optionally be the same as the layer of solid shielding material or a different layer, may reduce a size and weight of shield needed to achieve a selected shielding property, thereby enabling a radiation shield to be relocatable by logistical equipment commonly found in freight terminals. Some embodiments of the invention may be effective for reducing an amount of radiation escaping from a space containing a source of radiation. Some embodiments of the invention may be effective for preventing an amount of radiation from an external source from entering a space to be shielded.
The solid shielding material portion of the relocatable radiation shield comprises a shield block having at least one layer of material having a selected radiation shielding property, for example a layer of high density concrete optionally mixed with particles of steel, lead, or tungsten individually or in combination. The shield block may optionally comprise one or more additional layers, for example a layer of metal.
The layer adapted to contain a shielding fluid comprises a fluid container for holding a shielding fluid. A shielding fluid is a chemical compound in liquid solution effective for radiation shielding. An inlet fitting and an outlet valve enable shielding fluid to be drained from the fluid container, for example to reduce the weight of the radiation shield prior to relocation, and for the fluid container to be refilled after the radiation shield has been relocated. In some embodiments, the fluid container is formed from metal and is relatively rigid. In other embodiments, the fluid container is formed from a flexible material comprising a polymer compound and a metal having desirable shielding properties such as tungsten or lead. In other embodiments, the fluid container is a void formed in a layer of solid shielding material.
In some embodiments, a relocatable radiation shield has shape that facilitates placing at least two relocatable radiation shields in contact with each other to form an extended shield structure. In one embodiment, the relocatable radiation shield comprises a rectangular shield block and an approximately rectangular fluid container for holding shielding fluid with the fluid container attached on a side to a side of the shield block. In another embodiment, a fluid container is at least partially surrounded by the shield block. These embodiments may be used individually or stacked next to or on top of each other to form an extended radiation shield having a selected height, length, and thickness. Alternatively, a single relocatable radiation shield may have a length, a height, and a thickness to function as an effective radiation shield.
In some embodiments, a relocatable radiation shield is formed with a channel on a bottom side between opposite ends. A size the relocatable radiation shield and a size of the channel are selected to permit a vehicle such as a truck or train carrying a freight container to pass through the channel. Opposite ends of the relocatable radiation shield are shaped to enable assembly of an extended shielding structure comprising at least two radiation shields in close end-to-end contact. Some embodiments have at least one fluid container attached to the outside of the solid shield portion through which the channel is formed.
Some embodiments of a relocatable radiation shield are formed with angled ends. In some embodiments, an angle of a first end and an angle of a second end are the same. In some embodiments, an angle of an end is a right angle. Relocatable radiation shields having angled ends may be used in combination with other shields having angled ends or optionally with parallel ends to form an extended shielding structure for covering a path having a preferred shape.
Another embodiment of a relocatable radiation shield comprises a freight container. The freight container may alternatively be an isotainer with or without doors, a flat rack container, an open top container, a tunnel container, a platform container, or another type of freight container common in the shipping industry.
This section summarizes some features of the present invention. These and other features, aspects, and advantages of the embodiments of the invention will become better understood with regard to the following description and upon reference to the following drawings, wherein:
Embodiments of the invention include a relocatable radiation shield comprising a shield block and a fluid container adapted to hold a shielding fluid effective for absorbing radiation, for example liquid containing barium. The fluid container may be at least partially emptied to reduce weight and facilitate moving or maintaining the radiation shield. The relocatable radiation shield has a size and a weight that enables the shield to be moved by cranes or lifts commonly found in freight terminals, thereby enabling the relocatable radiation shield to be installed quickly and moved easily to accommodate desired changes in logistical flow. In some embodiments, the relocatable radiation shield has lifting hardware adapted for use by cranes and lifts such as gantry cranes and top handlers. Such lifting hardware, for example a corner fitting, is well known to manufacturers of freight containers, lifts, and cranes. In some embodiments the relocatable radiation shield has a size that is about the same as a size of a freight container. In other embodiments the relocatable radiation shield is formed with a channel large enough for a freight container on a trailer or train car to pass through the shield. Embodiments of the invention have ends shaped to enable two or more relocatable radiation shields to be placed in close contact to create extended shielding structures of a selected size.
An embodiment of a relocatable radiation shield 1 is shown in
The shield block 2 has a first selected radiation shielding property and comprises a layer of material having a first selected radiation shielding property, for example a material such as high-density concrete or high-density concrete mixed with particles of one or more metals such as, but not limited to, lead, tungsten, or steel. A sufficient quantity of another material, for example metal particles, may be mixed with the high density concrete to selectively alter a radiation shielding property. A radiation shielding property as used herein refers to a property of a material which causes a change in a measured amount of radiation as the radiation travels from a first location in the material to a second location in the material. In some embodiments, the shield block comprises more than one layer of shielding material wherein each layer has a selected radiation shielding property, a selected mechanical property such as strength, weight, or flexibility, or a combination of selected properties.
The fluid container 3 is formed from a relatively rigid material in some embodiments, for example, an alloy of steel or tungsten. In other embodiments, the fluid container 3 comprises a flexible polymer and a metal such as steel, lead, or tungsten in particulate form mixed with the polymer or in sheet or mesh form laminated in one or more layers to one or more layers of the polymer. The fluid container may optionally include reinforcing elements for maintaining a selected shape of the fluid container. A reinforcing element may include, but is not limited to, a reinforcing strap, a reinforcing patch, a portion of a fluid container wall having increased thickness, or a combination of these elements. An example of a fluid container 3 having a plurality of a reinforcing strap 12 is shown in
A relocatable radiation shield having a shield block further comprising a second layer of shielding material is shown in
The shield block 2 of
In the embodiments of
A relocatable radiation shield may optionally be formed with an internal fluid reservoir adapted to hold a shielding fluid. A relocatable radiation shield 1 having an internal fluid reservoir 11 is shown in
An extended shielding structure may be assembled from two or more relocatable radiation shields. Relocatable radiation shields may optionally be placed in end-to-end contact, side-to-side contact, or stacked one on another to assemble an extended shielding structure having a selected length, height, thickness, or radiation shielding property. An extended shielding structure may comprise combinations of the relocatable radiation shield embodiments described herein.
In another embodiment of a relocatable radiation shield, a channel is formed in a bottom side of a shield block to permit an object to be scanned to be pulled through the channel on a conveyance such as a vehicle or a train. The channel also provides space for radiation scanning equipment, for example radiation emitters and radiation detectors. In some embodiments, the channel is large enough to contain scanning equipment on a movable gantry or an equipment cart. In the embodiment of
The fluid containers 3 may optionally have connections to permit fluid to flow from one container to another. A fluid inlet fitting 4 on the top of the shield block 2 is connected to the first fluid container 3. A first outlet valve 5 on the first side of the shield block 2 is connected to the second fluid container 3 and a second outlet valve 5 on the second side of the shield block 2 is connected to the third fluid container 3. Alternatively, the three fluid containers 3 may be formed as a single fluid container. In other embodiments, the fluid containers are not connected for fluid flow between them and each fluid container has a separate fluid inlet fitting and outlet valve. In some embodiments, the fluid containers are rigid metal containers and in other embodiments they are flexible polymer containers. A relocatable radiation shield may optionally be formed with an internal fluid reservoir to hold a shielding fluid. An embodiment of a relocatable radiation shield 1 comprising a channel and an internal fluid reservoir 11 is shown in
In the embodiment shown in
In the embodiments illustrated in
In some embodiments, the first and second ends of a shield block are not parallel to each other. Instead, an edge of the first end is formed at a first selected angle to an edge of a side of the shield block and an edge of the second end is formed at a second selected angle to the edge of the side. A top view of a shield block 2 having angled ends and sloped sides is illustrated in
More than one relocatable radiation shield 1 having angled ends may be placed end-to-end to form an extended shielding structure for covering a curved path, as shown in
In another embodiment, a relocatable radiation shield comprises a freight container. In some embodiments the freight container is an isotainer.
In
The embodiment of
In the embodiment of
A relocatable radiation shield may optionally comprise a freight container that is unenclosed or partially enclosed. For example, the freight container may be a flat rack container, a platform container, or a tunnel container. An example of a relocatable radiation shield 1 comprising a partially enclosed freight container 15 of a type known as a flat rack container is shown in a top view in
The present disclosure is to be taken as illustrative rather than as limiting the scope, nature, or spirit of the subject matter claimed below. Numerous modifications and variations will become apparent to those skilled in the art after studying the disclosure, including use of equivalent functional and/or structural substitutes for elements described herein, use of equivalent functional couplings for couplings described herein, or use of equivalent functional steps for steps described herein. Such insubstantial variations are to be considered within the scope of what is contemplated here. Moreover, if plural examples are given for specific means, or steps, and extrapolation between or beyond such given examples is obvious in view of the present disclosure, then the disclosure is to be deemed as effectively disclosing and thus covering at least such extrapolations.
Unless expressly stated otherwise herein, ordinary terms have their corresponding ordinary meanings within the respective contexts of their presentations, and ordinary terms of art have their corresponding regular meanings.
