Abstract:
Materials and methods of manufacturing radiation shielded enclosures is presented that may replace the use of lead, granite and other undesirable materials and manufacturing methods. The present invention provides a high-density radiation shielding enclosure manufactured using a fiberglass lay-up or pressure spaying process and tungsten powder. The method of manufacture may include applying a tungsten powder in an epoxy, caulking, sealant, adhesive or elastomeric compound to the radiation shielding enclosure in order to seal any cracks, holes, joints or other radiation leaks.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention pertains generally to the field of radiation shielding, and more particularly to materials and methods of manufacturing radiation shielding enclosures and sealing radiation leaks in radiation shielding enclosures.  
         BACKGROUND OF THE INVENTION  
         [0002]    There are numerous uses for an x-ray shielding container, such as medical x-ray machines and industrial vision inspection machines. For example, x-ray detection is used to image dense objects, such as human bones, that are located within the body. Another application of x-ray detection and imaging is in the field of non-destructive electronic device testing. For example, x-ray imaging is used to determine the quality of solder that is used to connect electronic devices and modules to printed circuit boards.  
           [0003]    X-ray imaging works by passing electromagnetic energy at wavelengths of approximately 0.1 to 100×10 −10  meters (m) through the target that is to be imaged. The x-rays are received by a receiver element, known as an x-ray detector, on which a shadow mask that corresponds to the objects within the target is impressed. Dark shadows correspond to dense regions in the target and light shadows correspond to less dense regions in the target. In this manner, dense objects, such as solder, which contains heavy metals such as lead, can be visually distinguished from less dense regions. This allows the solder joints to be inspected easily.  
           [0004]    X-ray radiation is dangerous to living beings and the environment. Therefore, x-ray equipment is typically contained within an x-ray shielding container.  
           [0005]    The shielding containers in x-ray applications have typically been built from welded steel frames with plates of lead or sheets of granite attached for shielding. Plate lead shielding is very expensive and the sheets of lead are difficult to attach to an enclosure to form a shielded enclosure. A lead enclosure typically requires steel or other exterior enclosure to protect the lead shielding from damage. Lead is also a highly toxic material, making its use in medical, industrial and commercial settings undesirable. It is also very difficult to seal holes, cracks, joints, seams and other leak points in a lead enclosure.  
           [0006]    Although granite is not a toxic material, granite-shielding enclosures suffer many of the same shortcomings as lead shielding enclosures. Granite is also very heavy and difficult to manufacture and work with. As most radiation leakage will occur around seams, joints or holes, granite must be worked with in large sheets for large medical and industrial enclosures. This makes working with and transporting a granite enclosure very difficult due to the weight of the enclosure. Moreover, granite composites typically have poor radiation shielding characteristics.  
           [0007]    Accordingly, there exists a need for an environmentally safe, low cost, lightweight radiation shielding enclosure with good radiation shielding properties. In particular, a need exists for a radiation shielding enclosure made of a shielding material other than lead or granite.  
         SUMMARY OF THE INVENTION  
         [0008]    An apparatus for enclosing and shielding x-ray imaging and inspection equipment using tungsten rather than lead or granite is provided. The radiation shielding enclosure may be manufactured with a lay-up process using condensed tungsten powder in an epoxy or polyester substrate and fiberglass or other fabric sheet material to cover a form of the enclosure and/or to provide structural reinforcement.  
           [0009]    The radiation shielding enclosure may also be manufactured with a pressure spray process using condensed tungsten powder, cut fibers and an epoxy, polyester, or other suitable substrate capable of being pressurized and sprayed onto a form of the enclosure. A method for sealing cracks, seams, holes and leaks in an x-ray equipment container is provided.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    A more complete appreciation of this invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
         [0011]    [0011]FIG. 1 is a schematic diagram illustrating an exemplary x-ray imaging system;  
         [0012]    [0012]FIG. 2 illustrates a radiation shielding enclosure in accordance with the invention;  
         [0013]    [0013]FIG. 3 illustrates a flow chart of a process for forming a radiation shielding enclosure in accordance with one embodiment of the invention;  
         [0014]    [0014]FIG. 4 illustrates a flow chart of a process for sealing radiation leaks in a radiation shielding enclosure in accordance with the present invention; and  
         [0015]    [0015]FIG. 5 illustrates a flow chart of a process for forming a radiation shielding enclosure in accordance with a second embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    As shown in the drawings for purposes of illustration, the present invention relates to techniques for providing a radiation shielding enclosure. While described below with particular reference to an x-ray imaging system and with particular illustration of an x-ray imaging system for inspecting solder on printed circuit boards (PCB), embodiments of the invention are applicable in other x-ray systems.  
         [0017]    Turning now to the drawings, FIG. 1 illustrates an exemplary x-ray imaging system  100  in which an x-ray detector  200  resides. The x-ray imaging system  100  includes an x-ray source  102  and a plurality of x-ray detector assemblies, an exemplary one of which is illustrated using reference numeral  200 . A plurality of x-ray detectors  200  is typically supported on an x-ray detector assembly fixture (hereinafter detector fixture)  110 .  
         [0018]    The x-ray detectors  200  and the detector fixture  110  are coupled to an image-processing module  120  via connection  114 . The image-processing module  120  is coupled to a controller  125  via connection  138 . Each image-processing module  120  may receive input from one or more x-ray detectors, depending on the desired processing architecture.  
         [0019]    A controller  125  is coupled to the image-processing module  120  via connection  138 . The local interface  138  may be, for example, but not limited to, one or more buses or other wired or wireless connections, as known to those having ordinary skill in the art. The local interface  138  may have additional elements, which are omitted for simplicity, such as buffers (caches), drivers, and controllers, to enable communications. The user interface  136  may be any known or developed I/O device or user interface, such as, a keyboard, a mouse, a stylus or any other device for inputting information into the controller  125 .  
         [0020]    The controller  125  may be coupled to a display  118  via connection  116 . The display  118  receives the output of the controller  125  and displays the results of the x-ray analysis.  
         [0021]    In operation, the x-ray imaging system  100  can be used, for example, to analyze the quality of solder joints formed when components are soldered to a printed circuit board (PCB). For example, a PCB  104  includes a plurality of components, exemplary ones of which are illustrated using reference numerals  106  and  108 . The components  106  and  108  are generally coupled to the PCB  104  via solder joints. The x-ray imaging system  100  can be used to inspect and determine the quality of the solder joints. Although omitted for simplicity, the PCB  104  may be mounted on a movable fixture that is controlled by the controller  125  to position the PCB  104  as desired for x-ray analysis.  
         [0022]    The x-ray source  102  produces x-rays generally in the form of an x-ray radiation pattern  112 . The x-ray radiation pattern  112  passes through portions of the PCB  104  and impinges on an array of x-ray detectors  200 . As the x-rays pass through the PCB  104 , areas of high density (such as solder) appear as dark shadows on the x-ray detectors  200 , while areas of less density (such as the material from which the PCB is fabricated), appear as lighter shadows. This forms a shadow mask on each x-ray detector  200  corresponding to the density of the structure through which the x-rays have passed. Although omitted for simplicity, the controller  125  also controls the x-ray source.  
         [0023]    As will be described in further detail below, each x-ray detector  200  is constructed and located within the x-ray imaging system  100  so as to receive the x-ray energy from the x-ray source  102  after it passes through the PCB  104  or other target to be analyzed, examined, or radiated, such as food, living tissue, humans or animals. The x-ray detector  200  converts the x-ray energy to an electrical image signal that is representative of the shadow mask that falls on the x-ray detector  200 . The electrical image signals from all of the x-ray detectors  200  are sent to the controller  125 . The image processing module processes the signals, which can then be provided as an output to the display  118 .  
         [0024]    It will be readily appreciated that the present x-ray imaging system  100  is a high level representation of an x-ray imaging system for purposes of example only. Other x-ray imaging system configurations  100  and other targets  104  for analysis, examination or radiation are anticipated, such as flesh, humans, animals, food, mail, etc.  
         [0025]    Generally, it is desirable to contain the x-rays within an enclosure. This is because x-rays tend to degrade certain electronic devices and are hazardous to living creatures and the environment.  
         [0026]    [0026]FIG. 2 shows a radiation shielding enclosure  300  of tungsten composite with main body  304  and lid  302 . Radiation shielding enclosure  300  may have joints  310 , sealed with a tungsten composite compound and input/output holes  320 , sealed with a tungsten composite compound. FIG. 2 shows an x-ray imaging system  100 , such as an x-ray imaging printed circuit inspection system. X-ray imaging system  100  is shown merely for example purposes. Other industrial, manufacturing, and medical radiation emitting systems may be enclosed and shielded with the tungsten radiation shielding enclosure  300  of the present invention.  
         [0027]    [0027]FIG. 3 shows a flow chart for a manufacturing process according to a first embodiment of the present invention. A lay-up process  410  is used on a form to make a tungsten compound and fiber material radiation shielding enclosure. The tungsten compound may be powder tungsten and resin, polyester or epoxy substrate. The tungsten material used in the compound is a condensed form of tungsten powder. Most commercially available tungsten powders are precipitates, which do not have the high-density property of solid tungsten. Therefore the powder must be pressure and heat formed or sintered into a solid material and then returned to the powdered form by means of grinding, cutting, or a similar process. This allows the compound to use the highest possible density tungsten powder and increases the shielding ability of the compound. The tungsten compound may contain any physically similar polymerized synthetic or chemically modified natural resins including thermoplastic materials such as polyethylene and thermosetting materials such as polyesters that are used with stabilizers and other components to form plastics. The substrate may be formed by air, heat, or UV curing or thermosetting. The fiber may be any fabric material, such as a mesh or fabric form of fiberglass. The enclosure  300  may be a one-piece enclosure formed with the fiberglass fabric material and the tungsten compound using a hand lay-up process on a mold, similar to that used in the boat hull manufacturing industry or the swimming pool industry. The tungsten compound may be thermosetting or air-drying.  
         [0028]    This process permits the radiation enclosure to be more environmentally friendly than a lead radiation shielding enclosure  300  by using nontoxic materials. The tungsten radiation shielding enclosure  300  also has cheaper material, shipping and manufacturing costs than most other radiation shielding enclosures. This process of manufacture also reduces the fasteners and adhesives used in manufacturing a radiation shielding enclosure, providing an integrated shielding enclosure with fewer seams, butt joints, overlaps, or holes which require additional processes and parts to shield.  
         [0029]    Next, any cracks, joints, worm holes, rivet holes or other material mis-fit areas  310  or  320  where radiation may leak from the structure may be filled by an air or thermosetting tungsten compound  430 . The tungsten compound may contain tungsten powder and an epoxy, caulk, sealant, sealant or other known elastomeric material. Once an x-ray imaging system or other radiation system is installed in the tungsten radiation shielding enclosure  300 , any power cords, input/output cables or other devices that need to protrude or extend through the radiation shielding enclosure  300  may be threaded through any necessary holes in the enclosure and the tungsten sealing compound may be used to seal around any such cable holes in the radiation shielding enclosure  300 . Radiation leaks in the radiation shielding enclosure may also be sealed using a tungsten powder in an epoxy or polyester substrate with a fiberglass lay-up method, rather than with the tungsten sealant/caulking method.  
         [0030]    With reference to FIG. 4 illustrates a flow chart for filling radiation leaks in a radiation shielding enclosure in accordance with the present invention. An x-ray imaging system  100  is installed  500  into the radiation shielding enclosure  300 . Any power, communication, I/O, signal or other cables  142 ,  114  are routed  510  through cable routing vias  320  in the radiation shielding enclosure  300 . The void space between any cables  142 ,  114  and cable routing vias  320  in the radiation shielding enclosure  300  are sealed with a tungsten/fiber caulking sealant compound. The tungsten/fiber caulking sealant compound may contain tungsten powder and any known elastomeric, epoxy, sealant, caulking or other similar material and is applied in a wet solution and allowed to air dry. Alternatively, the void space between cables  142  and  114  and cable routing vias  320  may be sealed with a tungsten/cut fiber compound by means of a pressure spray process.  
         [0031]    Referring now to FIG. 5 a flow chart for a method of manufacturing a radiation shielding enclosure  300  according to a second embodiment of the present invention. A tungsten/fiber compound is pressure sprayed  610  onto a radiation shielding enclosure mold. The tungsten/fiber compound may contain tungsten powder and cut fibers such as fiberglass in an epoxy or polyester substrate capable of pressure spraying and thermosetting or air-drying. Next, any radiation leaks are located  620  and sealed by means of tungsten caulking sealant, tungsten compound in a lay-up process or by means of tungsten/fiber pressure spraying process  630 .  
         [0032]    Installing an x-ray imaging system into the radiation shielding enclosure, routing cables through cable vias and filling voids may then be done as described above and in FIG. 4.  
         [0033]    It will be appreciated from the above detailed description that a mesh, cloth or foil cloth of nylon, polyester, polyethylene, glass compound polyester, metal cloth, carbon fiber cloth, fiberglass cloth, stainless steel fiber, glass fiber reinforced plastic, braided sleeve material or other known cloth material may be used with a tungsten powder in an epoxy, polyester substrate, polymeric binder, nylon 12.RTM, resin, plastic or other known air drying or thermosetting type binder material capable of being used in a lay-up type process. The relative amount of tungsten powder used in the tungsten compound will determine the radiation shielding characteristics of the radiation shielding enclosure, but is preferably 5-95 percent of the tungsten compound by weight. The tungsten powder is preferably 2-40 microns in diameter.  
         [0034]    Although this preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention, resulting in equivalent embodiments that remain within the scope of the appended claims. For example, the tungsten lay-up process may be used to seal cracks, holes, joints, screw or rivet holes or other material mis-fit areas of a conventional lead or other radiation shielding enclosure or to manufacture an entire, integral enclosure using a mold and lay-up process.