Abstract:
An irradiation system includes a radiation source providing radiation in a localized radiation exposure area and a shielding structure around the radiation source. A conveyance system transports product into the shielding structure, through the radiation exposure region and out of the shielding structure. The conveyance system includes an input portion for carrying the product into the shielding structure at a first elevation. A first elevator moves the product from the first elevation to a second elevation different from the first elevation. A processing portion of the conveyance system carries the product at the second elevation through the radiation exposure region. A second elevator moves the product from the second elevation to a third elevation different from the second elevation. An output portion of the conveyance system carries the product out of the shielding structure at the third elevation.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of Provisional Application No. 60/191,028 filed Mar. 21, 2000 for “Irradiation System With Compact Shield” by S. Lyons, S. Koenck, B. Daiziel, D. White and J. Kewley. 
     INCORPORATION BY REFERENCE 
     The aforementioned Provisional Application No. 60/191,028 is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an irradiation system, and more particularly to a system having a compact shield arrangement for containing radiation within the system to ensure the safety of operating personnel. 
     Irradiation technology for medical and food sterilization has been scientifically understood for many years dating back to the 1940&#39;s. The increasing concern for food safety as well as safe, effective medical sterilization has resulted in growing interest and recently expanded government regulatory approval of irradiation technology for these applications. The available sources of ionizing radiation for irradiation processing consist primarily of gamma sources, high energy electrons and x-ray radiation. The most common gamma source for irradiation purposes is radioactive cobalt 60 which is simple and effective but expensive and hazardous to handle, transport, store and use. For these reasons, electron beam and x-ray generation are becoming the preferred technologies for material irradiation. An exemplary maximum electron beam energy for irradiation purposes is on the order of 10 million electron-volts (MeV) which results in effective irradiation without causing surrounding materials to become radioactive. The necessary electron beam power must be on the order of 5 to 10 kilowatts or more to effectively expose materials at rates sufficient for industrial processing. 
     Electron beam and x-ray irradiation systems both employ an electron accelerator to either emit high velocity electrons directly for irradiation or to cause high velocity electrons to collide with a metal conversion plate which results in the emission of x-rays. A number of electron acceleration techniques have been developed over the past several decades including electrostatic acceleration, pumped cylindrical accelerators and linear accelerators. 
     Electrostatic accelerators are characterized by the use of a direct current static voltage of typically 30 to 90 kilovolts which accelerates electrons due to charge attraction. Electrostatic accelerators are limited in maximum energy by the physical ability to generate and manage high static voltage at high power levels. Electrostatic accelerators using Cockroft-Walton voltage multipliers are capable of energy levels of up to 1 MeV at high power levels, but the 10 MeV energy level utilized by many systems for effective irradiation is not typically available. 
     Various types of pumped cylindrical electron beam accelerators have been known and used for many years. These accelerators generally operate by injecting electrons into a cylindrical cavity, where they are accelerated by radio frequency energy pumped into the cylinder. Once the electrons reach a desired energy level, they are directed out of the cylinder toward a target. 
     RF linear accelerators have also generally been in use for many years and employ a series of cascaded microwave radio frequency tuned cavities. An electron source with direct current electrostatic acceleration injects electrons into the first of the cascaded tuned cavities. A very high energy radio frequency signal driven into the tuned cavities causes the electrons to be pulled into each tuned cavity by electromagnetic field attraction and boosted in velocity toward the exit of each tuned cavity. A series of such cascaded tuned cavities results in successive acceleration of electrons to velocities up to the 10 MeV level. The accelerated electrons are passed through a set of large electromagnets that shape and direct the beam of electrons toward the target to be irradiated. 
     A typical industrial irradiation system employs an electron beam accelerator of one of the types described, a subsystem to shape and direct the electron beam toward the target and a conveyor system to move the material to be irradiated through the beam. The actual beam size and shape may vary, but a typical beam form is an elliptical shape having a height of approximately 30 millimeters (mm) and a width of approximately 45 mm. The beam is magnetically deflected vertically by application of an appropriate current in the scan deflection electromagnets to cause the beam to traverse a selected vertical region. As material to be irradiated is moved by conveyor through the beam, the entire volume of product is exposed to the beam. The power of the beam, the rate at which the beam is scanned and the rate that the conveyor moves the product through the beam determines the irradiation dosage. Electron beam irradiation at the 10 MeV power level is typically effective for processing of food materials up to about 3.5 inches in thickness with two-sided exposure. Conversion of the electron beam to x-ray irradiation is relatively inefficient but is effective for materials up to 18 inches or more with two-sided exposure. 
     In electron beam irradiation, high energy electrons are directed toward various food products which cause secondary radiation to be generated to penetrate deeply within the product. A byproduct of this beneficial secondary radiation is the generation of potentially harmful scattered radiation in the area of the system while it is operating. Consequently, radiation shielding is necessary to insure the safety of operating personnel. 
     Shielding requirements are determined by the power and the energy of the radiation source. Energy is related to the velocity of the accelerated electrons and generally determines penetration capability. Power is related to the number of accelerated electrons and generally determines exposure rate capability. For personnel safety, both parameters must be considered, as each contributes to the ability of radiation to penetrate shielding structures in amounts that must be limited for safe long term exposure by humans. 
     Electron beam irradiation systems maybe designed at various power and energy levels, with the maximum allowable energy established by the FDA and USDA at 10 MeV. This level has been selected as an upper bound due to the fact that no materials are activated and rendered radioactive by exposures at or below this level. While useful irradiation processing may be performed with electron beam energies as low as 1 MeV, the penetration depth that is possible at such energies is well less than 0.3 inches and is therefore limited in application. Energies of 10 MeV, however, allow two sided penetration up to 3.5 inches, which is useful for a wide variety of food products in final packaging. The disadvantage of the higher irradiation energy sources is the fact that shielding requirements are substantially greater to insure the safety of operating personnel. Typical 10 MeV systems are constructed within entire special buildings constructed of continuously poured high density concrete that may be as thick as 10 feet. Materials are typically moved to the radiation source by a conveyor that moves around a maze structure in circuitous fashion to insure that there is no straight line path for radiation to escape. While such structures are effective in providing safe operating conditions, they are also expensive and inefficient to construct and operate, and are difficult to add to an existing facility or production system. 
     There is a need in the art for an irradiation system employing a compact and yet effective shielding system for containing irradiation and preserving the safety of operating personnel. Such a system is the subject of the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is an irradiation system that includes a radiation source providing radiation in a localized radiation exposure area and a shielding structure around the radiation source. A conveyance system transports product into the shielding structure, through the radiation exposure area and out of the shielding structure. The conveyance system includes an input portion for carrying the product into the shielding structure at a first elevation. A first elevator moves the product from the first elevation to a second elevation different from the first elevation. A processing portion of the conveyance system carries the product at the second elevation through the radiation exposure area. A second elevator moves the product from the second elevation to a third elevation different from the second elevation. An output portion of the conveyance system carries the product out of the shielding structure at the third elevation. This configuration allows the shielding structure to have a reduced size in comparison to prior art irradiation systems, so that the irradiation system may be more easily added to existing processing facilities, or simply installed in a smaller area. The compact shielding structure may also be built for less cost than the concrete bunker required by many prior art irradiation systems. 
     In another embodiment, the conveyance system includes first and second input portions for carrying the product into the shielding structure and first and second output portions for carrying the product out of the shielding structure. A first elevator moves the product from the first input portion at first elevation to a second elevation different from the first elevation, and a second elevator moves the product from the second input portion at the first elevation to the second elevation. A first transfer portion of the conveyance system controllably transfers the product from the first and second elevators to a processing portion of the conveyance system for carrying the product through a localized radiation exposure area, and on to a second transfer portion of the conveyance system for controllably passing the product. A third elevator moves the product passed from the second transfer portion at the second elevation to the first output portion of the conveyance system at a third elevation different from the second elevation, and a fourth elevator moves the product passed from the second transfer portion at the second elevation to the second output portion of the conveyance system at the third elevation. This embodiment potentially increases the throughput of the irradiation system, and provides a redundant product path to reduce down time in the case of failure of one of the input portions or output portions of the conveyance system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side section view of an irradiation system employing a compact shielding module and an elevator assembly according to a first embodiment of the present invention. 
     FIG. 2 is a side section view of an irradiation system employing a compact shielding module and dual path elevator assemblies according to a second embodiment of the present invention. 
     FIG. 3 is a top section view of the irradiation system shown in FIG.  2 . 
     FIG. 4 is a schematic cross-sectional view through the center of the irradiation system shown in FIG.  2 . 
     FIG. 5 is a section view taken at line  5 — 5  of FIG.  3 . 
     FIG. 6 is a perspective diagram of a shield component piece according to an embodiment of the present invention. 
     FIG. 7 is a section view of the shield component piece shown in FIG.  6 . 
     FIG. 8 is a perspective diagram of a shield component piece including an attachment mechanism according to an embodiment of the present invention. 
     FIG. 9 is a section view of the shield component piece shown in FIG.  8 . 
     FIG. 10 is a perspective diagram of a shield component piece including a receiving chamber for an attachment mechanism according to an embodiment of the present invention. 
     FIG. 11 is a section view of the shield component piece shown in FIG.  10 . 
     FIG. 12 is a diagram of a shield structure constructed from a plurality of horizontally offset stacked shield component pieces according to an embodiment of the present invention. 
     FIG. 13 is a diagram illustrating the general configuration of a border portion of the shielding structure according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a side section view of irradiation system  100  employing a compact shielding module and an elevator assembly according to a first embodiment of the present invention. Irradiation system  100  employs electron beam accelerator  101  with energy as high as 10 MeV, and does not require a special concrete bunker structure to provide the necessary safety shielding for operating personnel. Irradiation system  100  is shown in FIG. 1 with a two sided exposure structure using single accelerator  101 , but a single sided exposure system could use the described shielding system equally effectively. Accelerator  101  accelerates electrons to an energy of up to 10 MeV and directs the electrons through output aperture  102  downward to upper scan horn  103 , and through bending magnet  104  to lower scan horn  105 . The two sided exposure system uses electromagnets in a manner generally known in the art to alternately deflect electrons either toward upper scan horn  103  (to direct the electrons by a second electromagnet toward the top of the material to be irradiated) or past upper scan horn  103  to bending magnet  104  that directs the beam back upward through additional electromagnets into lower scan horn  105  (to direct electrons toward the bottom of the material to be irradiated). Material to be irradiated is typically packaged in boxes that are moved at constant and controlled speed past the localized radiation area defined by upper and lower scan horns by conveyors  106  and  107 . Center roller  108  moves at the same speed as conveyors  106  and  107  to support product boxes as they move from the infeed conveyor  106  to the outfeed conveyor  107 . While the general concept of a conveyor system is known in the art of irradiation systems, irradiation system  100  of the present invention employs a novel compact self-shielded structure  110  that completely surrounds the high energy radiation-producing portions of the system. Shielding structure  110  is composed of radiation absorbing material such as steel, concrete, lead or a combination of those materials, placed closely around entrance  111  and exit  112  of irradiation system  100 . A box of material to be irradiated is inserted at entrance  111  by being placed on powered entrance rollers or conveyor  113  which moves the box toward position  114 . Elevator carrier  115  with powered rollers is positioned in elevator shaft  116  to elevate the box to a level even with infeed buffer rollers  117 . When elevator carrier  115  reaches the same level as infeed buffer rollers  117 , it is stopped and the rollers of elevator carrier  115  and infeed buffer rollers  117  move the box off elevator carrier  115  and into a position to be moved to infeed conveyor  106 . When elevator carrier  115  is empty, it returns to the lower position to receive another box from entrance rollers  113 . 
     Box  118  that has been placed on infeed buffer rollers  117  is moved onto infeed conveyor  106  at a speed generally faster than the speed of infeed conveyor  106  and outfeed conveyor  107  as soon as it is determined by position sensors located near infeed conveyor  106  that there is a space available and the previous box being irradiated will not be bumped by the new one being loaded. 
     A similar process is used to move boxes from outfeed conveyor  107  onto outfeed buffer rollers  119 . These rollers may also generally move at a speed faster than infeed conveyor  106  and outfeed conveyor  107  and are timed with the position of output elevator carrier  121  to insure that the elevator is located in its upper position to receive a box at position  120 . When the box is loaded at position  120 , output elevator carrier  121  is moved to the lower position to place the box even with exit rollers  122  and out exit  112  of irradiation system  100 . When output elevator carrier  121  is empty, it returns to the upper position to receive another box from outfeed buffer rollers  119 . 
     The movement of boxes from entrance rollers  113  through irradiation system  100  may be controlled by a Programmable Logic Controller (PLC) of typical industrial type. Sensors may be placed at various locations through the material flow process to monitor the movement and insure that operation is occurring as desired. The goal of the material handling system is to move boxes into the system, up the elevator and onto infeed conveyor  106  at a rate that keeps boxes positioned as close as possible to each other without touching to maximize the throughput of irradiation system  100  without upsetting the precise irradiation exposure ensured by the constant speed of the material moving through the localized radiation exposure area defined by scan horns  103  and  105 . 
     In an exemplary embodiment, the overall size of the described system is on the order of 24 feet long, 11 feet wide and 17 feed tall. The actual shielding thickness may vary from the illustration depending on the locations of the highest intensity of scattered radiation. The generally rectangular shape and conveyor material movement is compatible with production conveyor systems and is compact enough to be place inside typical processing and material handling facilities. Boxes containing materials of density similar to water such as meat up to 3.5 inches thick may be irradiated effectively. The total height of the boxes in the present example may be up to 6 inches thick, however, dimensions may be modified to increase or decrease sizes for particular applications. 
     FIG. 2 is a side section view of irradiation system  200  employing a compact shielding module and dual elevator assemblies according to a second embodiment of the present invention. Irradiation system  200  includes at least one accelerator (not shown in FIG. 2 for purposes of clarity) for accelerating electrons to an energy as high as 10 MeV, and directs the electrons through scan horns  203  and  205  shown schematically in FIG.  2 . The two sided exposure system may be realized in the manner described above with respect to FIG. 1, or may employ dual accelerators, for example. For purposes of illustration, irradiation system  200  will be described and shown as utilizing dual accelerators. 
     Product boxes to be irradiated are moved at constant and controlled speed past a localized radiation area (defined by upper scan horn  203  and lower scan horn  205 ) by conveyors  206  and  207 . Center roller  208  moves at the same speed as conveyors  206  and  207  to support product boxes as they move from infeed conveyor  206  to outfeed conveyor  207 . Shielding structure  210  completely surrounds the high energy radiation-producing portions of irradiation system  200 . Shielding structure  210  is composed of radiation absorbing material such as steel, concrete, lead or a combination of those materials, placed closely around entrances  211   a  and  211   b  (FIG. 3) and exits  212   a  and  212   b  (FIG. 3) of irradiation system  200 . 
     FIG. 3 is a top section view of irradiation system  200  shown in FIG. 2, illustrating the dual path elevator configuration of the system. Accelerators  228   a  and  228   b  are provided within shield structure  210  to direct accelerated electrons through scan horns  203  and  205 , respectively. Boxes of material to be irradiated are inserted at entrances  211   a  and  211   b  by being placed on powered entrance rollers or conveyors  213   a  and  213   b , which moves the boxes toward position  214  on elevator carriers  215   a  and  215   b . Elevator carriers  215   a  and  215   b  with powered rollers are positioned in elevator shafts  216   a  and  216   b , respectively, to elevate the boxes to a level even with transfer area rollers  230 . The system is controlled so that a product box is moved from a selected one of elevator carriers  215   a  and  215   b  to transfer area rollers  230  when the selected elevator carrier reached the same level as transfer area rollers  230 , and the selected elevator carrier is stopped at that level. Transfer area rollers  230  move the product box positioned thereon to infeed buffer rollers  217  and into a position to be moved to infeed conveyor  206 . When the selected one of elevator carriers  215   a  and  215   b  is empty, it returns to the lower position to receive another box from the appropriate one of entrance rollers  213   a  and  213   b.    
     Box  218  (FIG. 2) that has been placed on infeed buffer rollers  217  is moved onto infeed conveyor  206  at a speed generally faster than the speed of infeed conveyor  206  and outfeed conveyor  207  as soon as it is determined by position sensors located near infeed conveyor  206  that there is a space available and the previous box being irradiated will not be bumped by the new one being loaded. 
     A similar process is used to move boxes from outfeed conveyor  207  onto outfeed buffer rollers  219 . These rollers may also move at a speed faster than infeed conveyor  206  and outfeed conveyor  207 , and are operable to move product boxes to transfer area rollers  232 . Transfer area rollers  232  are timed with the position of output elevator carriers  221   a  and  221   b  to insure that one of the elevators is located in its upper position to receive a box at position  220 . When the box is loaded at position  220 , the selected one of output elevator carriers  221   a  and  221   b  is moved to the lower position to place the box even with the appropriate one of exit rollers  222   a  and  222   b , and out the corresponding one of exits  212   a  and  212   b . When the selected elevator carrier is empty, it returns to the upper position to receive another box from transfer area rollers  232 . 
     Similar to the single path system described above with respect to FIG. 1, dual path elevator irradiation system  200  may be controlled by a PLC of typical industrial type, with sensors placed at various locations through the material flow process to monitor the movement and insure that operation is occurring as desired. The goal of the material handling system is to move boxes into the system, up the elevators and onto infeed conveyor  206  at a rate that keeps boxes positioned as close as possible to each other without touching to maximize the throughput of irradiation system  200  without upsetting the precise irradiation exposed ensured by the constant speed of the material moving through the localized radiation exposure area defined by scan horns  203  and  205 . By utilizing dual input and output material movement paths and dual input and output elevators, the throughput of irradiation system  200  may be increased in some embodiments in comparison to the single path system, since the potentially limiting speed of the elevators in moving between their lower positions and upper positions is effectively doubled by employing two elevators in parallel. In addition, should one of the elevators employed in irradiation system  200  fail, the system can still operate with a single elevator (albeit at potentially reduced throughput), protecting against the possibility of a full shutdown which would be quite problematic for the typically time-sensitive applications of food irradiation, for example. 
     FIG. 4 is a schematic cross-sectional view through the center of irradiation system  200  shown in FIG. 2, illustrating dual accelerators  228   a  and  228   b  within shielding module  210  in more detail. Accelerators  228   a  and  228   b  are operable to accelerate electrons to energies up to 10 MeV and direct the accelerated electrons through scan horns  203  and  205  onto material to be irradiated. Alternatively, a single accelerator could be used with appropriate electromagnets for deflecting the beam through an upper and lower path, as generally described above with respect to FIG.  1 . 
     FIG. 5 is a section view taken at line  5 — 5  of FIG. 3, illustrating the configuration of output elevator carriers  221   a  and  221   b  and transfer area rollers  232  in more detail. Elevator carriers  221   a  and  221   b  are operated in an exemplary embodiment to alternately move between an upper position for receiving a box from transfer area rollers  232  (as shown by elevator carrier  221   a ) and a lower position for moving a box through the exit of the irradiation system (as shown by elevator carrier  221   b ). 
     Although the present invention has been described with respect to machine-generated irradiation, it should be understood that alternate embodiments of the invention may employ other sources of radiation that are known in the art. These alternate sources of radiation are generally not directable by electromagnets as described above with respect to machine-generated electron beams, but may be configured to expose product to radiation in a localized radiation area having a similar arrangement to the devices shown in FIGS. 1-5. 
     The elevator configuration employed by the present invention, in conjunction with the shielding structure around the irradiation system, is effective to insure that radiation is contained within the shielding structure and is unable to escape into areas where operating personnel may be present. As illustrated in FIGS. 1 and 2, shielding structures  110  and  210  are configured in such a manner that there is no line-of-sight path for radiation to escape from the irradiation processing area to the exits of the irradiation system, due to the 90 degree turn and change in elevation provided by the elevators employed by the system. Moreover, by utilizing elevators to provide 90 degree turns in the material movement path, the overall footprint of the self-shielded irradiation system can be made much smaller than prior art irradiation systems, with a floor area of 264 square feet in an exemplary embodiment of irradiation system  100  shown in FIG. 1, and a floor area of 494 square feet in an exemplary embodiment of irradiation system  200  shown in FIGS. 2-5. 
     FIG. 6 is a perspective diagram, and FIG. 7 is a section view, of shield structural component  300  according to an exemplary embodiment of the present invention. Structural component  300  has a roughly tubular shape, with outer material layer  302  defining an inner chamber to be filled with shielding material  304 . In an exemplary embodiment, outer material layer  302  is composed of a strong structural material such as steel or stainless steel, and shielding material  304  is composed of a radiation attenuating material such as lead. An exemplary height H of structural component  300  is about 2 inches, and an exemplary width W of structural component  300  is about 8 inches. A shield (such as shield  110  (FIG. 1) or shield  210  (FIG.  2 )) can be constructed with a plurality of structural components  300  stacked and interconnected with one another. In an exemplary embodiment, each structural component  300  has an intrinsic strength sufficient to support its own weight and the weight of an adjacent structural component (in the event that the adjacent structural component should structurally fail). Structural components  300  may optionally be constructed with sufficient strength to support the weight of more than one adjacent structural component, for additional safety against structural failure. 
     FIG. 8 is a perspective diagram, and FIG. 9 is a section view taken along line  9 — 9  of FIG. 8, illustrating structural component  300   a  designed to interconnect with other structural components to form a radiation shield according to an embodiment of the present invention. Structural component  300   a  includes outer material layer  302  with shielding material  304  in the inner chamber defined thereby, and also includes apertures  310  extending at least partially through outer material layer  302  and shielding material  304 . As shown in FIG. 9, in an exemplary embodiment apertures  310  are solid cylindrical plugs that include a drilled hole and a countersink for receiving fasteners  312 . Fasteners  312  may be of a type known in the art, such as a threaded bolt in an exemplary embodiment, for connection to adjacent structural components. 
     FIG. 10 is a perspective diagram, and FIG. 11 is a section view taken along line  11 — 11  of FIG. 10, illustrating structural component  300   b  designed to interconnect with structural component  300   a  (FIG. 8) to form a radiation shield according to an embodiment of the present invention. Structural component  300   b  includes outer material layer  302  with shielding material  304  in the inner chamber defined thereby, and also includes threaded apertures  320  extending at least partially through outer material layer  302  and shielding material  304 . As shown in FIG. 1, in an exemplary embodiment apertures  320  are solid cylindrical plugs that include a threaded hole for receiving fasteners  312 . Fasteners  312  may be of a type known in the art, such as a threaded bolt in an exemplary embodiment, for connection to adjacent structural component  300   a  (FIG.  8 ). 
     In an exemplary embodiment, structural components  300  are liquid-tight in construction, so that shielding material  304  can be installed by pouring molten material such as lead into the chamber defined by outer material layer  302  through an access port. In one embodiment, molten shielding material is poured into structural components  300  after the solid cylindrical plugs have been inserted in apertures  310  and  320  and welded in place, further securing fasteners  312  in place in addition to the threading of apertures  320 . Structural components  300  may be closed by welding a steel cap on each end, or by another suitable method known in the art. 
     Structural components  300   a  and  300   b  shown in FIGS. 8 and 10 are illustrated with apertures  310  and  320  located so that structural components  300   a  and  300   b  interconnect in a fully aligned fashion. In an exemplary embodiment of the present invention, apertures  310  and  320  are offset in such a manner that structural components  300   a  and  300   b  are stacked with a horizontal offset from one another. FIG. 12 is a diagram illustrating a horizontally offset shielding stack according to an embodiment of the present invention. Structural components  300  are horizontally offset from one another in adjacent vertical layers, so that the seams between structural components  300  are not vertically aligned. Lines A and B shown in FIG. 12 illustrate two paths for radiation to travel through the offset shielding structure. The vertical path shown by line A travels through a relatively small number of seams between structural components  300 , due to the horizontal offset of adjacent layers of those components. The diagonal path shown by line B travels through a larger number of seams between structural components, which would have a tendency to attenuate the radiation less, since the seams are composed of a structural material such as steel or stainless steel that attenuates radiation less than the shielding material (such as lead) contained therein. However, since the path of line B with high numbers of aligned seams is diagonal, the radiation must pass through a greater thickness of shielding material than it would for a vertical path, since the radiation passes through the shielding material at an angle rather than vertically. This arrangement of structural components  300  therefore minimizes the required total thickness of the shielding structure. 
     An entire shielding structure may be realized by interconnecting a plurality of structural components in the manner shown in FIG.  12 . The side borders of the shielding structure are realized in a similar manner, with the end components flipped to a vertical orientation. FIG. 13 is a diagram illustrating the general configuration of a border portion of the shielding structure. Structural components  300  are arranged so that horizontal and vertical components abut one another, and are interconnected by fasteners  312 , similar to the interconnection shown in FIG.  12 . Based on the exemplary portions of the shielding structure shown in FIGS. 12 and 13, it is within the expertise of one skilled in the art to construct the entire shielding structure of the present invention. Moreover, a number of modifications to the size, shape and/or arrangement of structural components  300  may be made within the scope and spirit of the shielding configuration of the present invention. 
     The present invention provides an irradiation system with a compact shielding structure for containing radiation within the system to ensure the safety of operating personnel. The irradiation system employs elevators to effect a 90 degree turn/change in elevation that permits the shielding structure to contain radiation by eliminating any straight line paths for radiation to escape from the system. An exemplary embodiment of the shielding structure is modularly constructed with a plurality of appropriately arranged structural components designed for both mechanical strength and shielding capability. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.