Abstract:
A particle accelerator ( 10 ) is disposed between a first shielded processing chamber ( 12 )and a second shielded processing chamber ( 14 ). The accelerator selectively feeds a higher energy (e.g., 10 MeV) electron beam to the first processing chamber and selectively feeds a lower energy (e.g., 5 MeV) electron beam to the second processing chamber. A conveying system ( 16 ) transports article carriers to and through the first processing chamber. At a processing table ( 18 ), the articles are conveyed at a closely controlled speed through the electron beam for uniform dosing of an article to be irradiated. A loading station ( 20 ) and an unloading station ( 22 ) supply and remove articles from the first processing chamber. Beam bending magnets ( 44 ) change the direction of an electron beam between the first processing chamber and the second processing chamber. A second conveying system, such as a reel-to-reel system ( 40 ) for processing articles of indefinite length transported on reels and rolls, conveys articles through the second processing chamber.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to irradiation systems. The invention finds particular relation to an irradiation system in which an accelerator selectively supplies electron beams to either of a pair of processing chambers and will be described with particular reference thereto. It is to be appreciated that the invention will also find application in other radiant energy systems. 
     Irradiation systems are used for irradiating articles, such as foodstuffs, food utensils, medical devices, consumer goods, cosmetics, and waste products and their containers, with high energy electromagnetic radiation, such as an electron beam, x-rays, and microwaves, for various purposes including sterilizing or disinfecting such articles. Articles are also irradiated in conjunction with cross polymerization of plastics and other material. 
     Heretofore, articles have been irradiated by utilizing a treatment application system that includes a radiation source, a plurality of article carriers, and a process conveyor for transporting the article carriers past the radiation source. The radiation source is mounted, for example, perpendicular to the conveyor along an approximately horizontal axis to irradiate the articles as they are transported past the radiation source. 
     In some systems, the article carriers are suspended from a power-and-free overhead conveyor. After the article carrier has been transported past the radiation source, some systems rotate the article carrier 180° and transport the reoriented article carrier past the radiation source again. In this manner, the irradiation during the initial transportation past the radiation source is symmetrically balanced. In one prior system, the article carrier is suspended from the power-and-free conveyor track at both its leading and trailing ends. It is reoriented by diverting the leading end to an unpowered branch track that loops off to one side and then rejoins the main track. The trailing end moves along the powered main track so that the trailing end takes the lead and pulls the diverted end from the branch track to the main track in a trailing position. 
     Other systems utilize a radiation source, article carriers, and several inverted conveyor systems (i.e., the chain is on the bottom of the conveyor). The conveyor system includes transport conveyors for loading/unloading, a process conveyor, and a stabilizing conveyor to stabilize movement of the article carrier. The transport conveyor transfers the carrier directly to the process conveyor. 
     However, existing systems do not provide for irradiating at different energy levels or in two different processing chambers using one centrally located accelerator. 
     Accordingly, it has been considered desirable to develop a new and improved irradiation system which would overcome the foregoing difficulties and others and which would produce better and more advantageous overall results. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, an irradiation system comprises a radiation source, a first processing chamber positioned adjacent the radiation source, and a second processing chamber positioned adjacent an opposite side of the radiation source. The first processing chamber and the second processing chamber are positioned opposite each other. The radiation source selectively feeds an electron beam to one of the processing chambers and selectively feeds an electron beam of a different energy level to the other of the processing chambers. 
     The radiation source provides an electron beam of a high energy level, such as 10 MeV, to the first processing chamber. The radiation source provides a low energy level electron beam, such as 5 MeV, to the second processing chamber. The 10 MeV and 5 MeV beams are not provided simultaneously. The radiation source further includes a rotary particle accelerator and beam bending magnets which change the direction of an electron beam generated by the particle accelerator between the first processing chamber and the second processing chamber when selected. 
     A conveying system is provided for transporting article carriers through the first processing chamber. The conveying system comprises a code system for tracking articles as they are transported through the first processing chamber. 
     A reel-to-reel system is provided for feeding articles of indefinite length through the second processing chamber. 
     One advantage of the present invention is that it reduces accelerator costs when there is a need for two accelerators (5 MeV and 10 MeV) at a single location. 
     Another advantage of the present invention is that it provides multiple energy levels, such as a 10 MeV electron beam and a 5 MeV electron beam. 
     Yet another advantage of the present invention is that it reduces reconfiguring time and cost for processing different types of articles by quick switching between 10 MeV treatment and the 5 MeV treatment. 
     Still another advantage of the present invention is that it reduces down time due to set up and preparation. 
     Yet still another advantage of the present invention is that medical products and food can be processed in the 5 MeV vault. 
     Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take physical form in certain parts and arrangements of parts. The drawings are for purposes of illustrating a preferred embodiment and are not to be construed as limiting the invention. 
     FIG. 1 is a plan view of a single accelerator and two-treatment vault system in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a plan view of the conveying system for the 10 MeV vault of FIG. 1; 
     FIG. 3 is a cross-sectional perspective view of a Rhodotron™ accelerator of the system of FIG. 1; 
     FIG. 4 is a computer screen for monitoring 10 MeV safety system status; and 
     FIG. 5 is a computer screen for monitoring 5 MeV safety system status. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1, a centrally located particle accelerator  10 , preferably a Rhodotron™electron accelerator, selectively feeds electron beams to a plurality of destinations. The accelerator is tapped such that different beams have different energies. 
     In a preferred embodiment, a 10 MeV beam is delivered to a first processing vault  12 ; and a 5 MeV beam is provided to a second processing vault  14 . The first processing vault  12  is positioned adjacent the accelerator  10  on one side of the accelerator. The second processing vault  14  is positioned adjacent the accelerator  10  on an opposite side of the accelerator. Optionally, additional vaults can be provided. 
     One advantage of using two different vaults, a 10 MeV vault and a 5 MeV vault, is that one accelerator can be used for irradiating different types of articles without the need for reconfiguring a processing vault for irradiating different types of articles. Medical devices can be irradiated with the 10 MeV system without the potential for contamination of the medical device by other items using either the 10 MeV system or the 5 MeV system. Conversely, the 5 MeV system is used for industrial products without potential for contamination to either the industrial products or medical products. 
     With particular reference to FIG. 2, the 10 MeV electron beam irradiation system includes the accelerator  10 , the first processing vault  12 , a product conveying system  16  with a separate process table  18 , an inbound product loading non-processed area  20  and an outbound processing storage and unloading area  22  and a process control system (not shown). The system processes carriers  24  of articles stacked on slave pallets by exposing the articles to a controlled source of electrons generated by the electron beam accelerator  10 . 
     The article carriers  24  are slaved to the power and free conveying system  16 , and they receive and transport the individual slave pallets with product through the first processing chamber  12 . The conveying system  16  transports the carriers  24  into and out of the first processing chamber  12 . Each article carrier  24  is identified by a unique license plate that allows for tracking that specific carrier throughout the entire system. The slave pallets are typically made of mild steel. The accelerator  10  is slaved to the conveyor system  16  speed. Thus, if the conveyor system  16  speed varies, the beam power of the accelerator  10  is adjusted accordingly. Alternatively, the accelerator  10  has a set parameter to which the conveyor speed is adjusted as the carrier passes the accelerator. 
     Articles on the slave pallet are stretch-wrapped to ensure their loading integrity and proper orientation to the electron beam. The loaded slave pallet is then transferred to the main conveying system  16  where a coding system  25  tracks the articles by bar code marks on the articles as they move through the system, as well as establishing the correct operating parameters for the process table  18  and accelerator  10 . The bar code mark is a label affixed to the articles which list customer and quality assurance information. The information is downloaded into a computer to generate a certificate of processing after irradiation. 
     In a preferred embodiment, the pallets are  105  cm long by 90 cm wide. Articles are stacked on the slave pallets, e.g., to a height of 180 cm. The slave pallets are removed from the unloading area  22  and are transferred by a forklift back to the loading area  20  where they index into the product palletizer. 
     For the 10 MeV system, articles are loaded onto slave pallets in a warehouse storage area, the slave pallets are transferred to the carriers  24 , and the carriers  24  are automatically conveyed by the conveyor system  16  into the first processing chamber  12 . The process control system assures that the speed of the process table  18  and the power of the beam are each set to assure the correct radiation dose. This system provides a redundant monitorying of speed and beam power for validation purposes. The process table  18  is positioned inside the first processing chamber  12  to ensure uniform dosing in front of the electron beam. If double-sided irradiation is required, the system moves the slave pallets to a rotating mechanism  26  that provides a 180-degree article orientation. A different slave pallet is returned to the vault for irradiation. The different slave pallet is used as a way to document that the product was rotated. 
     The product slave pallets are then transported to the processed storage and unloading area  22  for unloading. The carriers  24  and empty slave pallets are transferred back to the loading station  20 . 
     In the processed storage area  22 , the slave pallets are transferred to an unloading station  27  where stretch-film is removed and the product is configured for shipment back to the customer. A barrier fence separates a non-irradiated storage area from an irradiated storage area to assure that product must pass through the electron beam to reach the irradiation area. 
     With reference again to FIG. 1, a radiation shield  28 , e.g., of concrete about 3 meters thick, encloses the entire processing area that houses an electron scan horn  30  of the accelerator  10  and the process table  18 . The radiation shield  28  is designed to reduce the energy of 10 MeV x-rays generated in the processing area to an outside average exposure rate of less than 0.25 mrem/hour. This allows a person who works near the shield forty hours per week an accumulative exposure level of approximately 500.0 mrem per year. 
     Personnel and product enter the first processing chamber  12  through mazes that protect shield integrity and prevent the leakage of radiation. Personnel can enter through an access passage  32  when the radiation is off. Product is transported by the conveyor system  16  through a separate entry port  34  and exit port  36 . 
     With reference to FIG. 3, the accelerator  10  produces 80 kW of power and 8 mA of current to generate the 10 MeV electron beam. This power represents throughput capacity equivalent to approximately seven million curies of cobalt radioisotope. Located in its own concrete enclosure or vault  38 , the accelerator  10  generates electrons. The electrons are magnetically accelerated spiraling outward with increased energy. At the radius corresponding to the selected energy, the electrons are magnetically deflected into evacuated tubes. Magnets along the tubes guide the electron beam through the tubes without impacting the walls to the scan horn  30 . When the electron beam reaches the scan horn  30 , it is magnetically deflected into a planar fan that emerges from a window of the scan horn and passes into the first processing vault  12 . The entire accelerator, beam line and scan horn are maintained under deep vacuum to assure beam integrity and uniformity. An accelerator control system is set in order to deliver electron current at multiple levels, providing a wide range of processing capability. 
     With reference again to FIG. 1, for 5 MeV processing, a reel-to-reel conveying system  40  is used in one embodiment to process industrial products such as wire, cable, tubing or other products that are stored and transported on reels or rolls. The 5 MeV vault has a large opening to allow for large items to be driven on a forklift into the irradiation chamber. The reel-to-reel system  40  is used for industrial products of indefinite length and allows the 5 MeV vault to be smaller than if a bulky pallet conveying system was used. A second conveying system is used in combination with the reel-to-reel system  40  to process articles through the second processing chamber  14 . The reel-to-reel system  40  is slid away from the scan horn  30  when a processing table (not shown) is moved into place. The articles to be irradiated are transferred from the reel-to-reel system  40  to the second conveying system. 
     The system consists of payoff and take-up stands, a dual drum capstan within the second processing chamber  14 , and various adjustable tensioning and guide roller assemblies. The system preferably processes products ranging in diameter from about 1 cm to about 4 cm. Automated processing controls in conjunction with the accelerator  10  at the 5 MeV energy level allow the system to deliver very precise dose ranges. 
     A separate scan horn  42 , vertically positioned, is used with the accelerator  10  for the 5 MeV system. The scan horn  30  is horizontally positioned and approximately along the same plane as the first and second processing chambers  12 ,  14 . 
     The process of changing from 10 MeV to 5 MeV is accomplished by turning off one beam bending magnet  44  (shown in FIG.  3 ). The ability to switch back and forth between the two processing chambers  12 ,  14  provides the advantage of allowing workers to set up and prepare one of the vaults while the other vault is being used to irradiate articles. The shielding between the two chambers is sufficient to allow workers to be within one chamber while the other chamber is supplying electron beams to articles without exposing the workers to unacceptable radiation levels. 
     Switching the accelerator  10  between the two vaults  12 ,  14  can be done very quickly, typically in less than five minutes, using a computer control system. Thus, there is a minimal amount of downtime when switching between the 10 MeV system and the 5 MeV system. Switching to the 10 MeV energy level is accomplished when the accelerator operator selects the desired beamline via a computer. The computer program to select the beamline is well known in the industry. 
     The magnet system for the 10 MeV beam line is computer controlled. Set points are selected for a steering magnet and a scanning magnet positioned between the accelerator and the scan horn. To switch to the 10 MeV system, a bending magnet  44  is turned on and is used to provide the beamline to the 10 MeV vault. Similarly, parameters for a scanning magnet and a steering magnet are selected for the 5 MeV beam line. 
     The accelerator magnet system is also computer controlled. The various magnet parameters are changed or set by a computer control screen for the 10 MeV energy level or the 5 MeV energy level. The operation of the magnets for either the 10 MeV or 5 MeV systems are selected on a separate computer screen. 
     Referring now to FIG. 4, a computer controlled safety system is used to ensure that the 10 MeV system operates with minimal possibility for failure. A computerized audit is in place to control shutdown faults for personnel safety, accelerator safety, and common faults (e.g., power, water flow, etc.). Delayed shutdown fault audits are also in place such as a water temperature warning and an air pressure check. An audit is run anytime a breach occurs in any part of the system. For example, when the 10 MeV vault is entered or the accelerator is started up and provided power, the fault checks for these parts of the system are triggered. 
     Referring to FIG. 5, a 5 MeV safety system is also computer controlled. Immediate shutdown fault audits are also in place for 5 MeV personnel safety, accelerator safety, the computer control system, and common faults. Also, beam stop cooling water flow and ozone removal fans in both the 5 MeV and 10 MeV vaults are interlocked through the computers to insure safe operation. 
     10 MeV safety system is active only when the 10 MeV beam is selected. The 5 MeV safety system is active only when the 5 MeV beam is selected. 
     The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.