Abstract:
A first robotic assembly transfers articles from carriers on a transport mechanism at a loading area to a first load conveyor. The conveyor transfers the articles to a process conveyor which moves the articles through a target region at a substantially constant speed. The process conveyor then transfers the articles to a second load conveyor. A second robotic assembly then transfers the articles to article carriers on the transport mechanism at an unloading area. The load and process conveyors may be divided into two tracks. First and second radiation sources respectively disposed at first and second gaps in the process conveyor in the target region respectively irradiate the articles in both tracks in opposite directions from positions above and below the articles. Articles on the tracks may be (a) diverged on the first load conveyor to separate the articles from the dividers, (b) converged on the process conveyor to minimize the width of the radiation sources and (c) diverged on the second load conveyor. If one of the radiation sources is not operative, the other source may irradiate the opposite sides of the articles during article movements sequentially on the first tracks of the first load conveyor, the process conveyor and the second load conveyor and then sequentially on the second tracks of the first load conveyor, the process conveyor and the second load conveyor. The articles are inverted during their transfer from the first track of the second load conveyor to the second track of the first load conveyor.

Description:
This application is a non-provisional application of a provisional application No. 60/141,781 filed in the United States Patent and Trademark Office on Jun. 30, 1999, for APPARATUS FOR, AND METHODS OF, STERILIZING PRODUCTS, PRIMARILY FOOD PRODUCTS in the names of John Thomas Allen, Gary K. Loda, George M. Sullivan and Colin Brian Williams as joint inventors. 
     This invention relates to systems for, and methods of, irradiating articles, and particularly food articles, to sterilize the articles. 
    
    
     BACKGROUND OF THE PREFERRED EMBODIMENTS 
     It has been known for some time that drugs and medical instruments and implements have to be sterilized so that they will not cause patients to become ill from harmful bacteria when they are applied to the patients. Systems have accordingly been provided for sterilizing drugs and medical instruments and implements. The drugs and the medical instruments and implements are then stored in sterilized packages until they are ready to be used. 
     In recent years, it has been discovered that foods can carry harmful bacteria if they are not processed properly or, even if they are processed properly, that the foods can harbor such harmful bacteria if they are not stored properly or retained under proper environmental conditions such as temperature. Some of these harmful bacteria can even be deadly. 
     For example, harmful bacteria have been discovered in recent years in hamburgers sold by one of the large national hamburger chains. Such harmful bacteria caused a number of purchasers of hamburgers from stores in the chain to become sick. As a result of this incident and several other similar incidents, it is now recommended that hamburgers should be cooked to a medium state rather than to a medium rare or rare state. 
     Similarly, harmful bacteria have been found to exist in many chickens that are sold to the public. In view of a number of incidents which have occurred, it is now recommended that all chickens be cooked so that no blood is visible in the cooked chickens. 
     To prevent incidents such as discussed in the previous paragraphs from occurring, various industries have now started to plan for sterilizing foods before the foods are sold to the public. This is true, for example, of hamburgers and chickens. It is also true of fruits, particularly fruits which are imported from foreign countries. 
     BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments may be used to sterilize different products including drugs and medical instruments and medical implements but are particularly adapted to be used for sterilizing foods. In sterilizing foods, it is important that the sterilization is sufficiently strong to kill harmful bacteria in the food but is not so strong as to kill beneficial bacteria in the foods. 
     In the preferred embodiments, a first robotic assembly transfers articles form carriers on a transport mechanism at a loading area to a first load conveyor. The conveyor transfers the articles to a process conveyor which moves the articles through a target region at a substantially constant speed. The load and process conveyors may be divided into two tracks. First and second radiation sources respectively disposed at first and second gaps on the process conveyor in the target region respectively irradiate the articles in opposite directions from positions above and below the articles. The process conveyor then transfers the articles to a second load conveyor. A second robotic assembly then transfers the articles to article carriers on the transport mechanism at an unloading area. 
     Articles on the tracks may be (a) diverged on the first load conveyor to separate the articles from the dividers, (b) converged on the process conveyor to minimize the width of the radiation sources and (c) diverged on the second load conveyor. 
     If one of the radiation sources is not operative, the other source may irradiate the opposite sides of the articles during article movements sequentially on the first tracks of the first load conveyor, the process conveyor and the second load conveyor and then sequentially on the second tracks of the first load conveyor, the process conveyor and the second load conveyor. The articles are inverted during their transfer from the first track of the second load conveyor to the second track of the first load conveyor. 
    
    
     BRIEF DESCRIPTION OF THE PREFERRED DRAWINGS 
     In the drawings: 
     FIG. 1 is a top plan of a system constituting a preferred embodiment of the invention for irradiating opposite sides of articles, and particularly foods, with electron beams to sterilize the articles; 
     FIG. 2 is an elevational view of one of two (2) robotic assemblies included in the preferred embodiment shown in FIG. 1, one for transferring the articles form a loading area to a first load conveyor and the other for transferring articles from a second load conveyor to an unloading area; 
     FIG. 3 is a top plan view of the robotic assembly shown in FIG. 2; 
     FIG. 4 is a top plan view of a process conveyor included in the preferred embodiment of the system shown in FIGS. 1-3; 
     FIG. 5 shows curves illustrating the intensity of the irradiation from opposite sides of an article at progressive distances through the article and illustrating the cumulative intensity of the radiation produced in the article at the progressive distances through the article; 
     FIG. 6 shows curves illustrating the cumulative intensity of the irradiation at progressive distances through the article when the distance between the opposite sides of the article is varied; 
     FIG. 7 is a chart showing the minimum and maximum irradiation intensities which are to be produced in the articles at the different positions in the articles; 
     FIG. 8 is a fragmentary plan view of apparatus which may be used in conjunction with the system shown in FIGS. 1-4 for irradiating opposite sides of an article with a single radiating source when the other of the two (2) radiation sources shown in FIG. 1 becomes inoperative; 
     FIG. 9 is an enlarged perspective view of a plurality of articles stacked in a non-uniform relationship on an article carrier movable on a transport mechanism toward the loading area; 
     FIG. 10 is an enlarged perspective view of a plurality of articles stacked in a uniform relationship on an article carrier movable on the transport mechanism toward the loading area; and 
     FIG. 11 is a schematic top plan view of a system constituting another preferred embodiment of the invention for irradiating opposite sides of an article, and particularly food, with electron beams to sterilize the article. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The preferred embodiments incorporate a number of the features disclosed in provisional application No. 60/141,781 filed in the United States Patent and Trademark Office (USPTO) on Jun. 30, 1999. The preferred embodiments also incorporate a number of the features disclosed and claimed in U.S. Pat. No. 5,396,074 issued to Richard O. Peck, Gary M. Pageau, Colin B. Williams, John T. Allen, Bernard G. Wickersham, Leonard C. Bisgrove and Bruce D. Sellers on Mar. 7, 1995, for an IRRADIATION SYSTEM UTILIZING CONVEYOR-TRANSPORTED CARRIERS and assigned of record to the assignee of record of this application. The preferred embodiments further incorporate features disclosed and claimed in U.S. application Ser. No. 08/854,202 (docket TITAN-49534) filed on May 9, 1997, in the USPTO in the names of John T. Allen, George M. Sullivan, Michael S. Brazell, Harold B. Knowles, Anthony A. Zante, Richard J. Mendonsa, Richard C. Miller and Kenneth Whitman for ARTICLE IRRADIATION SYSTEM IN WHICH ARTICLE-TRANSPORTING CONVEYOR IS CLOSELY ENCOMPASSED BY SHIELDING MATERIAL and assigned of record to the assignee of record of this application. In addition, the preferred embodiments incorporate features disclosed and claimed in U.S. application Ser. No. 09/102,942 (docket TITAN-49641) filed in the USPTO on Jun. 23, 1998, for ARTICLE IRRADIATION SYSTEM HAVING INTERMEDIATE WALL OF RADIATION SHIELDING MATERIAL WITHIN LOOP OF CONVEYOR SYSTEM THAT TRANSPORTS THE ARTICLES in the names of John T. Allen, George M. Sullivan and Colin B. Williams as joint inventors and assigned of record to the assignee of record of this application. Reference may be made to U.S. Pat. No. 5,396,074 and/or to any or all of the pending applications specified above to complete the disclosure in this application if the disclosure in this application is found inadequate in any respect. 
     A preferred embodiment of a system of the invention is generally indicated at 10. The system  10  includes a loading area, generally indicated at  12  (FIG.  1 ), for receiving articles  14  which are disposed in a stacked relationship in article carriers  16 . The articles may illustratively be drugs, drug instruments and/or drug implements. The articles may also illustratively and preferably be meats of various cuts such as hamburgers or may be chickens or fruits or juices or any of a wide variety of other foods. The articles  14  may actually be anything which harbors bacteria that are harmful to humans or animals and that will be destroyed when subjected to irradiation by the system  10 . In this way, the system  10  of this invention sterilizes the articles  14  for human or animal use or consumption. 
     The articles may be disposed in the article carriers  16  in a uniformly or non-uniformly stacked relationship. A uniformly stacked relationship of the articles  14  in one of the article carriers  16  is generally illustrated at  18  in FIG. 10. A non-uniformly stacked relationship of the articles  14  in another one of the article carriers  16  is illustrated at  20  in FIG.  9 . It will be appreciated that FIGS. 9 and 10 are only illustrative arrangements of the articles  14  in uniformly non-stacked and uniformly stacked relationships. 
     The article carriers  16  are transported on a transport mechanism generally indicated at  22 , past the loading area  12 . The direction of movement of the transport mechanism  22  is to the left in FIG. 1 as indicated by an arrow  24 . The articles  14  are removed from the article carriers  16  by a robotic assembly  26 , generally indicated at  26 , which may constitute a Pallet Cell 100/200 apparatus manufactured and sold by FANUC Robotics North America, Inc. 
     The transfer of the articles  14  from the article carriers  16  by the robotic assembly  26  may be controlled by a controller  28 . The controller  28  is programmed to consider the disposition of the individual ones of the articles  14  in the stacked relationship of the articles in the article carriers  16  on the transport mechanism  22  and to operate the robotic assembly  26  in accordance with this stacked relationship whether the stacked relationship be uniform (FIG. 10) or non-uniform (FIG.  9 ). 
     When the articles  14  are stacked in a uniform relationship (FIG. 10) in the article carriers  16 , the controller  28  causes the robotic assembly  26  to move each of the successive articles  14  in the article carriers  16  in the same path to a load conveyor  30  in the loading area  12  so that each of the articles will have a particular disposition on the loading conveyor. However, when the articles  14  are stacked in the article carriers  16  in a non-uniform relationship (FIG.  9 ), the controller  28  causes the robotic assembly  26  to move in a path which is adjusted to take account of the non-uniform relationship so that the articles will have the particular disposition on the load conveyor  30 . 
     The load conveyor  30  may transport the articles  14  at a selective speed such as approximately sixty feet per minute (60′/min) to approximately ninety feet per minute (90′/min). The speed of movement of the articles on the load conveyor  30  does not have to be regulated. The load conveyor  30  may be divided into two (2) tracks  30   a  and  30   b  of substantially equal widths as by a divider  32 . Articles  14  may be simultaneously disposed on each of the tracks  30   a  and  30   b . The articles on each of the tracks  30   a  and  30   b  may be the same as, or different from, the articles on the other one of the tracks. 
     The movement of the articles  14  on the tracks  30   a  and  30   b  may be provided by rollers  34  which may be driven by any suitable mechanism known in the art. At the position of transfer of the articles  14  to the load conveyor  30 , the rollers  34  may have a herringbone configuration as indicated at  34   a . In this configuration, separate rollers  34  may be disposed in each of the tracks  30   a  and  30   b  in an angled relationship to the rollers in the other track so that the end of the rollers adjacent the divider  32  is ahead of the end of the rollers distant from the divider in the direction of movement of the articles on the tracks. 
     In this way, the rollers  34  with the herringbone configuration  34   a  tend to displace the articles  14  from positions adjacent the divider  32  to positions displaced from the divider. This is desirable to insure that the movement of the articles  14  on the load conveyor  30  will not be impeded by bumping against the divider  32 . When the articles have been sufficiently displaced laterally from the divider  32 , the rollers are preferably provided with a configuration  36  in which the rollers are substantially perpendicular to the divider  32  and are substantially parallel to one another. 
     The load conveyor  30  may be formed from a plurality of segments  36   a ,  36   b ,  36   c ,  36   d ,  36   e ,  36   f  and  36   g , all of which are preferably disposed in a horizontal plane. The segments  36   a ,  36   b ,  36   d  and  36   f  may preferably constitute straight segments. The straight segments  36   a ,  36   b  and  36   f  may be disposed in a first direction and the straight segment  36   d  may be disposed in a second direction substantially perpendicular to the segments  36   a ,  36   b  and  36   f . The segments  36   c ,  36   e  and  36   g  may constitute curved segments each having a curvature of substantially 90°. The curved segment  36   c  joins the straight segments  36   b  and  36   d ; the curved segment  36   e  joins the straight segments  36   d  and  36   f ; and the curved segment  36   g  is contiguous to the straight segment  36   f.    
     A process conveyor generally indicated at  38  and having a horizontal disposition in the same plane as the load conveyor  30  is contiguous at one end to the curved segment  36   g  of the load conveyor  30 . The process conveyor  38  is constructed to move the articles  30  at a particular speed such as in the range of approximately thirty feet per minute (30′/min) to approximately sixty feet per minute (60′/min). This speed is preferably regulated by the controller  38  so that it is maintained within particular limits. If the speed should vary from these limits, the radiation applied to the articles  14  on the process conveyor  38  may be interrupted and the operation of the process conveyor may be discontinued. 
     The process conveyor  38  may be divided into two (2) tracks  38   a  and  38   b , as by a divider  40 , in a manner similar to the division of the load conveyor  30  into the two (2) tracks  30   a  and  30   b  by the divider  32 . The process conveyor may be provided with rollers  42  having a construction similar to the rollers  34  in the load conveyor  30 . The rollers  42  at the end of the process conveyor  38  adjacent to the load conveyor segment  36   g  has a herringbone configuration  42   a . The herringbone configuration  42   a  of the rollers  42  differs from the herringbone configuration  34   a  of the rollers  34  in that the ends of the rollers  42  distal from the divider  40  lead the end of the rollers adjacent the divider in the direction of movement of the articles  14  on the rollers. The rollers  42  accordingly operate to move the articles  14  on the tracks  38   a  and  36   b  to positions contiguous to the divider  40 . 
     The process conveyor is preferably divided into three (3) segments  39   a ,  39   b  and  39   c  (FIG.  4 ), in the direction of movement of the articles  14  on the tracks  38   a  and  38   b , to form a gap  44   a  between the segments  39   a  and  39   b  and to form a gap  44   b  between the segments  39   b  and  39   c . The segments  39   a ,  39   b  and  39   c  may respectively have lengths of approximately three feet (3′), ten feet (10′) and two feet (2′). The gaps  44   a  and  44  may have lengths of approximately one half of one foot (½′) in the direction of movement of the articles  14  on the process conveyor  38 . It will be appreciated that the articles  14  should preferably have a length greater than the lengths of the gaps  44   a  and  44   b  so that the articles will be simultaneously on the segments  39   a  and  39   b  as they traverse the gap  44   a  and the articles will be simultaneously on the segments  39   b  and  39   c  as they traverse the gap  44   b.    
     A radiation source  46  (FIG. 1) may be disposed to direct radiation through the gap  44   a  to the articles  14  on the process conveyor  38 . The radiation source  46  may be disposed in a vertical direction above the process conveyor  38  to direct light downwardly on the articles  14  on the process conveyor. Similarly, a radiation source  48  may be disposed below the process conveyor  38  to direct radiation upwardly through the gap  44   b  to the articles  14  on the process conveyor  38 . In this way the radiation will be directed against the opposite sides of the articles  14  on the process conveyor  38 . The intensities of the radiation from the sources  46  and  48  should preferably be substantially equal within particular limits. 
     The radiation sources  46  and  48  preferably provide an electron beam against the opposite sides of the articles  14  on the process conveyor  38 . Each of the radiation source  46  and  48  preferably provides an electron beam with an intensity of approximately ten (10) Mev. However, the beam can be of any intensity to kill harmful bacteria in the articles  14  being irradiated without killing beneficial bacteria in such articles. It will be appreciated that other types of radiation sources than those providing electron beams may be satisfactory, particularly in special situations. For example, gamma rays (as from cobalt or cesium) and X-rays may be satisfactory, particularly in specific instances. However, electron beams are generally preferred since they heat the articles only through a minimal range of temperatures and since the electrons directed toward the beams are only temporary in duration. For example, the temperature increase of beef patties when irradiated with an electron beam may be approximately 2° F. This allows frozen beef patties to remain frozen during and after the irradiation of the beef patties. 
     Electron beam radiation has a number of advantages, particularly for irradiating food, in addition to those discussed in the previous paragraph. These additional advantages include high dose rate, the ability to turn the radiation sources instantaneously on and off, the ability to regulate the irradiated area as by beam scanning, no source replenishments, the ability to regulate the strength of the radiation and the ability to operate in a dual mode (electron beam and X-ray). Other advantages of electron beam irradiation are relatively short exposure time, high power utilization in the fraction of the emitted energy usefully absorbed in the article being irradiated, simplified conveyor systems for the articles (e.g. the articles  14 ) because of the irradiation of individual articles rather than pallet-sized or tote-size loads and a minimization in the numbers (only 1 or 2) of passes of the articles  14  through the target region of the radiation source(s). 
     There are certain definite advantages to converging the articles on the tracks  38   a  and  38   b  toward the divider  40  on the process conveyor before the articles  14  reach the radiation sources  46  and  48 . By converging the articles  14  toward the divider  40 , the widths of the radiation from each of the radiation sources  46  and  48  are minimized. This minimizes the consumption of energy in the radiation sources  46  and  48 . Alternatively, it provides for an increase in the energy directed by the radiation sources  46  and  48  against the articles  14  on the process conveyor  38 . 
     As previously indicated, the speed of movement of the articles  14  on the load conveyor  30  is preferably greater than the speed of movement of the articles on the process conveyor  38 . If the proper ratio of speeds is selected (depending on the lengths of the articles  14 ), the spacing between successive articles on the process conveyor is minimized, thereby increasing the efficiency in the operation of the system and decreasing the amount of power not utilized. 
     The articles  14  on the process conveyor  38  are transferred to a load conveyor generally indicated at  50  (FIG.  1 ). The load conveyor  50  may have a construction similar to that of the load conveyor  30 . For example, a divider  52  may be provided to divide the load conveyor  50  into two (2) tracks  50   a  and  50   b  and rollers  54  may be provided on the load conveyor to advance the articles  14  on the load conveyor toward an unloading station generally indicated at  56 . The rollers  54  adjacent the process conveyor  38  may be provided with a herringbone configuration  54   a  similar to the herringbone configuration  34   a  of the rollers  34 . This facilitates the movement of the articles on the load conveyor  50 . The resultant separation of the articles  14  on each of the tracks  50   a  and  50   b  at the unloading station  56  facilitates the separate and individual handling of the articles at the unloading station. 
     The load conveyor  50  may be formed from several segments  58   a ,  58   b ,  58   c ,  58   d ,  58   e ,  58   f ,  58   g  and  58   h . The segment  58   a  is contiguous to the process conveyor  30  and is curved. The segment  58   b  is contiguous to the segment  58   c  and is also curved. However, the segments  58   a  and  58   b  have opposite curvatures so that the articles  14  passing from the segment  58   b  travel in an opposite direction through the segment  58   c  relative to the direction in which the articles pass from the process conveyor  38  to the segment  58   a . The segment  58   c  is a straight segment parallel to the process conveyor  38 . The segments  58   d  and  58   e  cumulatively provide a curvature of 180° in a manner corresponding to the segments  58   a  and  58   b . The segment  58   f  is straight and is parallel to the segment  58   c  but extends in a direction opposite to the direction of the segment  58   c . The segment  58   g  provides a curvature of 90° between the segments  58   f  and  58   h . The segment  58   h  extends in a direction parallel, but opposite, to the segment  36   a  in the load conveyor  30 . The segment  58   h  extends to the unloading area  56 . 
     A robotic assembly generally indicated at  60  may be disposed in the unloading area  56  to receive the articles  14  from the load conveyor  50  and to transfer the articles to the article carriers  16  on the transport mechanism  22 . The article carriers  16  may constitute those from which the articles  14  have been previously transferred to the load conveyor  30  in the loading area  12 . Because of this, the article carriers  16  adjacent to the unloading area  56  are empty. The articles  14  may be transferred to the load conveyor  50  in the unloading area  56  in a uniform relationship such as indicated at  18  in FIG. 10 or in any other uniform relationship or in a non-uniform relationship such as indicated at  20  in FIG. 9 or in any other non-uniform relationship. The transfer of the articles  14  from the load conveyor  50  to the article carriers  16  on the transport mechanism  22  in the uniform or non-uniform relationship may be under the control of the controller  28 . The robotic assembly  60  in the unloading area  56  may correspond in construction to the robotic assembly  26  in the loading area  12 . 
     The robotic assembly  26  includes a platform  62  (FIGS. 3 and 4) which is rotatable in a horizontal plane through an annulus indicated at  64  in FIG. 4. A support member  66  extends upwardly from the platform  64 . An arm  68  is pivotable in a vertical plane on a pin  70  as a fulcrum, the pin being disposed on the support member  66 . A strut  72  supported on the arm  68  is pivotable in a vertical plane on a pin  74 . A plate  76  is supported by the strut  70  for a rotary movement in a horizontal plane through an annulus indicated at  78  in FIG.  4 . 
     The platform  62  rotates in the horizontal plane to a position for disposition of the arm  68  in contiguous relationship to one of the articles  14  in one of the article carriers  16  on the transport mechanism  22 . The arm  68  is then pivoted on the pin  70  as a fulcrum to provide for the plate  74  to lift the article  14  from the article carrier  16 . The platform  62  is then rotated through a horizontal plane to the position of the load conveyor  30 . The plate  76  is thereafter rotated to the position for depositing the article  14  in a properly aligned relationship on the load conveyor  30 . The strut  72  is then pivoted downwardly on the pivot pin  74  as a fulcrum to deposit the article in the properly aligned relationship on the load conveyor  30 . 
     The inclusion of the two (2) tracks in each of the load conveyor  30 , the process conveyor  38  and the load conveyor  50  provides certain important advantages. It allows the articles  14  to be moved past the radiation sources  46  and  48  at one half (½) of the speed at which the articles  14  would move if only one (1) track were provided. A reduced speed is desirable because it simplifies the operation of the irradiating system  10 . Another advantage of providing the two (2) tracks in each of the load conveyor  30 , the process conveyor  38  and the load conveyor  50  is that one type of article  14  can be processed on one of the tracks at the same time that another type of article can be processed on the other track. 
     The inclusion of the radiation sources  46  and  48  to apply radiation respectively from positions above and below the articles  14  also provides certain important advantages. One advantage is that the use of the radiation sources  46  and  48  minimizes the time for processing the articles  14 . Another advantage is that the thickness of the article  14  being sterilized in each pass can be increased without increasing the intensity of the radiation from the sources  46  and  48 . 
     A further advantage is that the article  14  does not have to be inverted in order to apply radiation to the second opposite side of the article  14 . Inverting the article  14  is undesirable when products such as fresh meat patties are being pasteurized. This results from the fact that blood from what was originally the bottom side of the article  14  flows to what was originally the top side of the article when the article is inverted. This blood discolors the visual appearance of the article  14  when the article is again inverted so that what was originally the top side of the article again becomes the top side of the article. 
     Radiation shielding generally indicated at  78  in FIG. 1 may be applied to the system  10  (a) to limit the existence of radiation from the radiation sources  46  and  48  in areas other than the target region where the articles  14  are to be irradiated and (b) to prevent radiation from the sources from reaching the loading area  12  and the unloading area  56 . The radiation shielding  78  may be formed from a suitable material such as concrete. The radiation shielding  78  may encompass the system  10  and may include (a) a portion  80   a  adjacent the load conveyor segment  36   b , (b) a portion  80   b  adjacent the load conveyor segments  36   c ,  36   d  and  36   e , (c) a portion  80   c  adjacent the load conveyor segments  36   e ,  36   f  and  36   g , (d) a portion  80   d  adjacent the load conveyor segment  36   g , the process conveyor  38  and the load conveyor segment  58   a , and (e) a portion  80   e  adjacent the load conveyor segments  58   a ,  58   b ,  58   g  and  58   h . The radiation shielding segments  80   a - 80   e  are integral or continuous with one another. A radiation shielding portion  80   f  integral with the radiation shielding portions  80   a - 80   e  extends into the space between the load conveyor segments  58   c  and  58   f.    
     A radiation shielding member  82  made from a suitable material such as concrete and separated from the radiation shielding portions  80   a - 80   f  is disposed in the region between the process conveyor  38  and the load conveyor segment  58   c . The radiation shielding member  82  limits the amount of radiation passing to the radiation shielding portions  80   a - 80   c  and  88   e  and accordingly provides for a decrease in the thickness of these radiation shielding portions. The radiation shielding portions  80   a    80   f  and the radiation shielding member  82  are preferably integral with a floor (not shown) made from a suitable material such as concrete and a roof (not shown) made from a suitable radiation shielding material such as concrete. In this way, the system  10  is disposed within an enclosure made from a radiation shielding material such as concrete. 
     As previously described, the articles  14  may travel on the two tracks  30   a  and  30   b  of the load conveyor  30  from the loading area  12 , then on the two (2) tracks  38  and  38   b  of the process conveyor  38  and then on the two (2) tracks  50   a  and  50   b  of the load conveyor  50  to the unloading area  56 . During the movement of the articles  14  on the process conveyor  38 , each of the radiation sources  46  and  48  irradiates the articles  14  on the two tracks  38  and  38   b . However, it may sometimes happen that one of the radiation sources  46  and  48  may be inoperative to irradiate the articles  14  on the tracks  38   a  and  38   b  of the process conveyor  38 . Assume that it is the radiation source  46 . Under such circumstances, the other one of the radiation sources  46  and  48  (assume that it is the source  48 ) performs a double duty and irradiates the two (2) opposite sides of the articles  14  on the tracks  38   a  and  38   b  of the process conveyor  38 . 
     To provide for the radiation source  48  to irradiate the two (2) opposite sides of the articles  14 , an alternative load conveyor (one track wide), generally indicated at  84  in FIG. 8, is provided between the first track  50   a  of the load conveyor  50  and the second track  30   b  of the load conveyor  30 . The path of travel of the articles  14  is then the first track  30   a  of the load conveyor  30 , the first track  38   a  of the process conveyor  38  and the first track  50   a  of the load conveyor  50 . During this path of travel, the first side of the articles  14  is irradiated by the radiation source  48 . 
     The articles  14  then travel from the first track  50   a  of the load conveyor  50  through the alternate load conveyor  84  (one track wide) to the second track  30   b  of the load conveyor  30 . During this travel, the articles  14  reach a barrier  86 . To surmount this barrier, a lifting mechanism  88  is provided to lift the articles from the side of the barrier  86  adjacent the load conveyor  50  to the side of the barrier adjacent the load conveyor  30 . While the articles  14  are being lifted above the barrier  86 , they are inverted. The articles  14  then travel from the second track  30   b  of the load conveyor  30  to the second track  38   b  of the process conveyor  38 , then to the second track  50   h  of the load conveyor  50  and then to the unloading area  56 . The radiation source  48  irradiates the second opposite side of the articles  14  during this second movement of the articles  14  past the radiation source  48 . The same paths as described above in this paragraph and the previous paragraph are provided when the radiation  48  is unable to irradiate the articles  14  and the radiation source  46  irradiates the two (2) opposite sides of the articles. 
     A curve  90  in FIG. 5 shows the irradiation intensity produced in the article  14  at different depths in the article when radiation is provided from the source  46  downwardly on the article. As will be seen, the irradiation intensity increases for some distance downwardly from the top of the article  14  until it reaches a maximum value and then the irradiation dose decreases from that maximum value with further progressive distances downwardly through the article. FIG. 5 also shows an irradiation intensity  92  produced in the article  14  by the source  48 . As will be seen, the irradiation intensity from the source  48  increases for a particular distance upwardly through the article  14  from the bottom of the article to a maximum value and then decreases from that maximum value with further progressive distances upwardly through the article. The curve  92  may be considered as an inverse of the curve  90 . 
     A curve  94  in FIG. 9 constitutes a composite of the curves  90  and  92 . The composite curve  94  in FIG. 9 has a radiation intensity  96  at the top of the article  14 . This corresponds substantially to the radiation intensity at the top of the article  14  for the curve  90 . The intensity of the radiation in the composite curve  94  then increases from the dose  96  to a maximum value  98  at a position approximating in the article  14  the position at which the curve  90  has an irradiation intensity corresponding to the irradiation intensity in the curve  92 . 
     FIG. 6 illustrates composite curves for progressive increases in the thickness of the article  14 . The composite curve  94  in FIG. 5 is repeated in FIG. 6. A curve  100  in FIG. 10 constitutes a composite of the radiation intensities produced by the sources  46  and  48  when the thickness of the article  14  is increased by a first amount from the thickness of the article in the composite curve  94 . A curve  102  constitutes a composite of the radiation intensities produced by the radiation sources  46  and  48  when the thickness of the article  14  is increased by a second amount greater than the first amount from the thickness of the article  14  for the composite curve  94 . As will be seen for each of the composite curves  100  and  102 , the difference between the maximum and minimum radiation intensities increases as the thickness of the article  14  increases above the thickness of the article for the composite curve  94 . 
     FIG. 7 is a chart showing the range of irradiation intensities that the system described above should produce. For example, the irradiation system  10  should produce at least a first irradiation dose  110  in FIG. 7 at every position in the article  14  in order to reduce the number of harmful organisms such as  E - Coli , listeria and salmonella when the article is a beef patty. If the irradiation intensity at any position in the article  14  is below the value  110 , the harmful organisms (e.g.  E - Coli ) in the article may not be reduced sufficiently so that a person eating the beef patty can become sick. The radiation intensity should not exceed a second value  112  at every position in the article in order to preserve the life of beneficial organisms in such articles  14  as beef patties. As will be seen, the radiation intensity  112  is greater than the radiation intensity  110 . 
     As will be seen, the difference between the maximum radiation intensity  112  and the minimum radiation intensity  110  at different vertical positions in the article  14  increases with increases in the thickness of the article. It is desirable to maintain this difference within particular limits. On the other hand, it is desirable to maintain the ability of the system  10  to process as thick articles  14  as possible in order to maintain the versatility of the system. Success is accordingly achieved by providing an optimum thickness of the articles  14  at an optimum ratio of the maximum value  112  and the minimum value  110  of the radiation dose throughout the article and by providing these parameters at the lowest cost. 
     FIG. 11 illustrates another preferred embodiment, generally indicated at  200 , of a system constituting the invention. However, the system  200  is not as preferred as the system  10 . The preferred embodiment  200  shown in FIG. 11 includes a pair of radiation sources  202  and  204  respectively corresponding to the radiation sources  46  and  48  in the embodiment shown in FIGS. 1-4 and described above. The system  200  includes a load conveyor, generally indicated at  208 , having a straight portion  208   a  extending from a loading area  206 , a portion  208   b  having a curvature of substantially 90°, a straight portion  208   c  extending in a direction opposite to the straight portion  208   a , a portion  208   d  having a curvature of substantially 90° and extending in a direction opposite to the curved portion  208   b , a straight portion  208   e  extending in a direction corresponding to the straight portion  208   a , a portion  208   f  having a curvature of substantially 90°, a straight portion  208   g  extending in the same direction as the straight portion  208   c  and a portion  208   h  having a curvature of substantially 90°. 
     A process conveyor generally indicated at  209  extends from the load conveyor portion  208   h  in a straight path having a direction corresponding to the load conveyor portion  208   a . The radiation sources  202  and  204  are disposed at gaps in the process conveyor  209 . A load conveyor generally indicated at  211  extends from the process conveyor  209 . The load conveyor  211  has a curved portion  211   a , a straight portion  211   b , a curved portion  211   c , a straight portion  211   d , a curved portion  211   e , a straight portion  211   f , a curved portion  211   g  and straight portions  211   h  and  211   i . A curved portion may be disposed between the straight portions  211  h and  211   i . An unloading area  213  may be disposed at the end of the straight portion  211   i.    
     Radiation shielding material, generally indicated at  210 , such as concrete envelopes the system  200  to define a chamber. Radiation shielding material  212  such as concrete is disposed within the loop defined by the process conveyor  209 , the load conveyor portions  208   e - 208   h  and the load conveyor portions  211   a - 211   e  to define a wall. A wall  214  made from the radiation shielding material such as concrete extends integrally from the radiation shielding material  212  into the space between the curved portions  208   d  and  211   e . A roof and a floor made from a radiation shielding material such as concrete may also be provided in the embodiment shown in FIG.  11 . 
     The embodiment shown in FIG. 11 appears to have certain disadvantages relative to the embodiment shown in FIGS. 1-4 and described above. It appears to occupy more space than the embodiment shown in FIGS. 1-4. It also appears to require more radiation shielding material than the embodiment shown in FIGS. 1-4. Furthermore, the loading and unloading areas in the embodiment shown in FIG. 11 appear to be significantly removed from each other relative to the positioning of the loading area  12  and the unloading area  56  in the embodiment shown in FIGS. 1-4. This increases the difficulty of transferring the articles  14  between the loading  206  and the unloading area  213  in the embodiment shown in FIG.  11 . In view of the above, the embodiment shown in FIGS. 1-4 and described above appears to be the preferred embodiment in comparison to the embodiment  200  in FIG.  11 . 
     Although this invention has been disclosed and illustrated with reference to particular preferred embodiments, the principles involved are susceptible for use in numerous other embodiments which will be apparent to persons of ordinary skill in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.