Abstract:
A process irradiator includes a heavily shielded, generally cylindrical, housing with a heavily shielded top. A radiation source includes source elements in several tubes extending from the top into a shielded storage cask below the center of the housing floor. A circular track concentrically positioned relative to the track guides a motor-driven carousel carrying a number of turntables which carry material to be irradiated, the turntables being rotatable on their axes. A heavy shielded door provides access to the turntables which are successively rotated on the carousel to a position adjacent the door opening. A lifting structure on the top includes two or more lifting devices which permit selective lifting of the source elements from the storage cask into the housing. Interlock controls prevent the door from opening and the carousel from rotating unless all source elements are stored in the storage cask.

Description:
REFERENCE TO RELATED APPLICATION 
     This Non-provisional application claims benefit of U.S. Provisional Applications No. 60/107,260 filed Nov. 5, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     There is an established need for providing assurance of thorough and complete sterilization of medical equipment such as syringes, sutures, catheters, swabs, blood transfusion sets, petri dishes, scalpels and surgical gloves. These items have been routinely sterilized by cobalt 60 radiation. In addition it is useful to irradiate various food items with cobalt 60 radiation to retard spoilage and to assure that such products remain salable over a significant time period. 
     Because of danger of radiation damage to personnel, facilities for effecting the radiation have necessarily incorporated heavy shielded walls, floors and ceilings, which typically has required a separate building. To move the medical supplies or food items relative the radiation sources, expensive conveyor systems have been used. This combination of a separate building and an expensive conveyor system has resulted in a very costly installation. There is therefore a need for a simpler and less costly installation for providing process irradiation. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     This invention may be clearly understood with the following detailed description and by reference to the drawings in which: 
     FIG. 1 is a vertical sectional view of our process irradiator; 
     FIG. 2 is a sectional view taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a sectional view taken along line  3 — 3  of FIG. 1; 
     FIG. 4 is a sectional view taken along line  4 — 4  of FIG. 1; 
     FIG. 5 is a sectional view taken along line  5 — 5  of FIG. 1; 
     FIG. 6 is a fragmentary view, on an enlarged scale of two irradiation sources shown in FIG. 1; and 
     FIG. 7 is a fragmentary sectional view, on an enlarged scale, of the circled part of FIG.  1 . 
    
    
     SUMMARY OF THE INVENTION 
     Applicants have devised a process irradiator whose outside dimensions are only about the size of a medium sized room (15 ft.×20 ft.) and which can readily be installed in a dedicated area of an existing building. The irradiator is assembled from components, none of which weigh as much as 15000 pounds, which permits assembly using readily available industrial fork lift trucks. 
     In one embodiment the irradiation chamber consists of a housing consisting of a generally cylindrical concrete wall 72 inches thick and having an opening on one side with a heavy shielding door. The door is mounted on a track such that it can be moved laterally to open or close the opening. A roof which is also of concrete 72 inches thick is supported on the generally cylindrical wall and on the top of the door. Centered in the floor of the irradiation chamber is a cylindrical shielded storage cask which is set in the ground and which is approximately 30 inches in diameter and 30 inches deep. Shielding for the cask is void free lead contained in a welded steel enclosure. The radiation sources are stored in tubes which extend from within the storage cask to which they are bolted to the ceiling where they are attached to additional tube sections which extend through the roof section to the drive or lift system which drives the radiation sources up and down within the tubes. The source drive system is mounted on the rooftop and is an electro-pneumatic system utilizing cable cylinders operated by solenoid valves for precise positioning. There may be two or more sets of sources which are driven separately or in any desired combination. 
     Surrounding the source tube array and concentric to the array is a circular track or rail carrying a rotatable carousel to which are attached a plurality, typically four, of turntables. Each turntable is driven rotatably by means of rotatable drive system. A clutch locks the turntables in place for engagement with the drive system. When the clutch is disengaged, the turntables can be moved around the rail to a position adjacent to the opening so that containers carrying the material to be irradiated can be separately placed on, or removed from, the turntables. When the turntables are all loaded with containers, the clutch is engaged so that the turntables can be rotated and the contents of the containers irradiated from the sources. Thus there are four turntables, each substantially equidistant from the source tubes, carrying containers which are being uniformly irradiated on all sides. 
     Various controls are provided to, inter alia, control the height of the sources to vary radiation levels and to provide interlocks such that the sources cannot be lifted from the storage cask until the door is closed and locked and the door cannot be opened until the sources are all properly housed in the storage cask. The source rods may be grouped so that different levels of radiation may be selected. A second embodiment is similar to that described above except that the cylindrical wall, roof and door are made of steel plates 30 inches apart and with the space between the plates filled with steel material such as steel shot. A third embodiment is similar to that described above except that the inner cylindrical wall and roof are made of steel plate, and earthen shielding is used for the wall and roof. This embodiment also uses a thick steel door as described above. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, which is a vertical sectional view of the process irradiator of the invention, the processor includes a housing  10  which is of generally cylindrical conformation having a concrete sidewall  12  approximately 72 inches thick and a top  14 , also of concrete approximately 72 inches thick. Carried on top  14  is a tower  16  which contains a lifting structure including cylinders  24 ,  25  and  26  connected through cables  28 ,  29  and  30  to a pair of lifting blocks  32  and  34 . Another cylinder and cable are not visible in this view. Each of blocks  32  and  34  carry a plurality of cobalt 60 sources which are supported on cables movable within a plurality of stainless steel guide tubes  35 . Tubes  35  are, in turn, located within and protected by a perforated cylindrical steel housing  36  which extends from top  14  through the floor  38  of the process irradiator  10 . Also visible in this view are a plurality of turntables  40   b  and  40   d.  Turntables  40   b  and  40   d  are connected by means of a plurality of vertical supports  41  to circular drive members  42   b  and  42   d  located near the top of housing  10  which carry chain sprockets  44   b  and  44   d,  respectively. Only a single vertical support  41  is shown connected between turntables  40   b  and drive member  42   b  and between turntable  40   d  and drive member  42   d  to avoid confusing the drawing. The numbers and locations of such supports will be obvious to those skilled in the art, it only being necessary to allow clearance for loading the turntables. The chain sprockets are part of a chain drive system, discussed in detail below, which includes a double sprocket idler assembly  46 . A motor  48  drives a chain  50  connected to assembly  46  through a belt or chain drive  52  to a right angle drive  54 , a clutch  56  and a shaft  58  terminating in a sprocket  60 . 
     On the floor  38  of housing  10  is a circular guide rail  62  which guides a plurality of rigid casters  64  around its periphery to assure that the turntables move around in the desired circle within housing  10 . Connected to motor  48  or another suitable motor is a sprocket  66  which transmits power through a chain  70  which serves to drive a rotatable carousel  72  upon which all the turntables are supported and rotated. 
     Block  73  shown connected to tower  16  contains controls including a central data processor and input devices which provide such functions as raising and lowering the cobalt 60 sources only when door  18  is closed, opening door  18  only when the sources are safely stored in the storage cask  76  etc. 
     The structure in housing  10  is more clearly shown in FIG. 2 which is a sectional view taken along line  2 — 2  of FIG.  1 . Shown in this view is housing  10 , turntables  40   a,    40   b,    40   c  and  40   d,  and the steel guard housing  36  shown enclosing a plurality of guide tubes  35 . 
     Turntables  40   a,    40   b    40   c  and  40   d  are movable on carousel  72  around circular rail  62  to a position adjacent an opening  17  and door  18  for loading and unloading of containers  44  which contain the material to be irradiated. The containers are dimensioned to fit on the turntables without interference with either the interior surface of sidewall  12  or guard housing  36  and can be stacked two or three high on the turntables. To avoid interference with door  18  which is closed during irradiation, the carousel  72  is rotated 45 degrees from the loading/unloading position as shown. If the material to be irradiated is supplied with other packaging, such packaging must be placed within the containers. Preferably, the turntables and the bottoms and tops of the containers  44  have mating grooves or projections to assure that the containers are properly positioned on the turntables and on each other. Since containers  44  are generally loaded on to the turntables by means of a forklift truck such grooves or projections should preferably be positioned to accommodate the tines of the forklift. 
     The cobalt 60 sources are suspended on rigid members movable within the guide tubes  35 . When the sources are not in use actively irradiating the contents of materials in the containers  44 , they are stored in a storage cask  76  which is buried in and below the level of floor  38  and directly below tower  16 . This storage cask is of void free lead lined with steel and is approximately 30 inches in diameter and 30 inches deep. Each of the sources includes a plug of tungsten shielding material  77  above the cobalt 60 material which effectively shields the inside of housing  10  from radiation from storage cask  46 . This shielding is sufficient to keep radiation levels within housing  10  to less than 5 mRem/hr at 12 inches directly above the cask around the cask protective housing  36  when the sources are in stored position in cask  46 . 
     The carousel  72  may be driven by means of motor  48  or another motor  48   a  shown secured in a shielded housing  12   a  to attached sidewall  12  and which drives a chain  70  which travels in tubes through sidewall  12 . Chain  70  wraps around the carousel  72  causing the carousel  72  to rotate from one loading and unloading position to the next. Certain supports and braces are shown in dashed lines which are positioned under and tend to support the carousel  72 . A pair of tensioners  78 ,  80  serve to keep chain  76  taut. This view also shows, in phantom, the circular rail  62  and a plurality of casters  64  which are positioned at intervals under each of the radial braces supporting carousel  72 . 
     Door  18  is movable to open and close opening  17  for loading and unloading. Since door  17  it is extremely heavy it is driven by motor  48  or other motor means on rollers  81  along a track. When the door  18  is open the containers may be loaded/unloaded onto or from the turntables by means of a forklift truck. Once one turntable is loaded, for example, the carousel is rotated 90° to place the next turntable in position for loading, etc. When all turntables are loaded, door  17  is closed carousel  27  is rotated 45° to clear door  18  and irradiation may begin. 
     FIG. 3 is a sectional view taken along line  3 — 3  of FIG.  1  and shows details of the drive structure for rotating drive wheels  42   a    42   b    42   c  and  42   d  which rotate turntables  40   a,    40   b,    40   c  and  40   d.  The main drive sprocket  60  drives chain  50  to rotate the double sprocket idler assembly  46 . A sprocket coaxial with the driven sprocket of assembly  46  drives a chain  82  which, in turn, drives sprocket  44   b  which rotates member  42   b  and, hence, turntable  40   b.  Another sprocket coaxial with sprocket  44   b  drives a chain  84  to drive a sprocket  44   c,  which, in turn, drives a coaxial sprocket, driving a chain  86  to rotate sprocket  44   d.  A second sprocket coaxial with sprocket  44   b  drives a chain  88  to rotate a sprocket  44   a.  In this way sprockets  44   b,    44   c,    44   d  and  44   a  serve to rotate members  42   b,    42   c,    42   d  and  42   a,  respectively, thereby rotating turntables  40   b,    40   c,    40   d  and  40   a  respectively. When the irradiation is completed the cobalt 60 sources are lowered into the storage cask  76  and door  18  may be opened and the containers  44  removed from the turntables. If there are more containers having materials to be irradiated the containers can be removed and replaced while each turntable is in position adjacent opening  17 . 
     FIG. 4 is a view, partly in section, taken along line  4 — 4  of FIG.  1 . In this view one is looking down on lifting blocks  32  and  34  within the tower  16 . A plurality of cobalt 60 sources are suspended from each of blocks  32  and  34  with one group (crosshatched) being suspended from block  32  and another group (in phantom) being suspended from block  34 . Block  32  is physically positioned above block  34  and carries a group of stainless steel guide tubes  35  having rigid members or rods connected to cobalt 60 sources contained within them. If it is desired to expose one or more containers to only the sources connected to block  32 , for example, block  32  is raised by means of actuator  25  and cable  30  and a corresponding actuator and rods not visible in FIG.  1 . The guide tubes  35  connected to block  32  pass through ports in block  34  as shown in FIG.  6 . 
     If a greater intensity of radiation is desired, both blocks  32  and  34  may be raised to lift all the sources out of storage cask  72 . 
     FIG. 5 is a cross-sectional view taken along line  5 — 5  of FIG.  1 . This view show both sets of source rods within their guide tubes  35  with rods from the groups cross-sectioned differently. 
     FIG. 6 is a fragmentary view on an enlarged scale of a pair of guide tubes  35  one connected to block  32  and the other connected to block  34  (not shown). A cobalt 60 source  98  is shown connected to a cable  92  which is connected to block  32 . A second guide tube  35  is secured to block  34 . This view shows that guide tubes  35  connected to block  32  are movable through ports  94  in block  34  to permit the sources connected to block  32  to be raised and lowered by moving through the ports  92  while leaving the guide tubes connected to block  34  stationary. This view also shows a tungsten shielding plug  77  in phantom in an alternate raised position. 
     FIG. 7 is an enlarged fragmentary view partly in section of the circled portion of FIG.  1 . The sprocket  60  drives a larger sprocket  96  which rotates around a bearing  28 . A second large sprocket  100  is connected through chain  82  to drive sprocket  44   b.  Coaxial with sprocket  44   b  is another sprocket  102  which drives sprocket  44   a  through chain  88 . 
     The above described embodiments of the present invention are merely descriptive of its principles and are not to be considered limiting. The scope of the present invention instead shall be determined from the scope of the following claims including their equivalents.