X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
1998-09-15
2001-04-10
Bruce, David V. (Department: 2876)
X-ray or gamma ray systems or devices
Specific application
Absorption
C250S453110
Reexamination Certificate
active
06215847
ABSTRACT:
The present invention relates to a multipurpose product irradiator. More specifically this invention relates to an irradiator useful in irradiating medical, food and other products or articles.
BACKGROUND OF THE INVENTION
Irradiation systems are used for irradiating medical devices, foodstuffs, food utensils, as well as other goods such as cosmetics, waste products and the like. Typically high energy ionizing radiation is used as the radiation source, for example gamma radiation, X-ray, electron beam, or the like. The source, in the case of a radioisotope, is typically maintained beneath the irradiation chamber within a pool when not in use, and raised into position as required. Articles of interest are placed upon pallets, or loaded into unique carrier trays, and these pallets or carriers are conveyed past the radiation source in order to expose the contents therein.
It is well known within the art, that even exposure of the article to the source will provide a more optimum irradiation. In this regard, the dose-uniformity ratio (DUR), which is the ratio between the maximum and minimum dose that a product receives, is used as a measure for exposure uniformity. In order to optimize the DUR, several conveyor-track assembly, and their relationship with radiation source locations have been considered.
Many prior art irradiators utilize conveyors in order to move a product laden carrier past an radiation source, for example U.S. Pat. Nos. 5,396,074, 5,001,352, 4,866,281, 4,852,138, 4,561,358, 4,481,652, 3,676,675 or U.S. Pat. No. 3,564,241. These irradiators utilize a source-overlapping-product configuration, and operate with a low efficiency of source utilization. Furthermore, these systems necessitate the use of many moving mechanical parts within the irradiation chamber, yet the environment within the irradiation chamber is hard on many plastics and metals. Such designs are therefore prone to repeated failures that require full shutdown of the irradiator for repair. Similarly, other transport systems, (U.S. Pat. Nos. 4,066,907, 4,018,348) use turntables coupled with conveyor systems to expose a product to a source. These systems also comprises many moving parts within the radiation chamber, and necessitate substantial product handling within the irradiation chamber. Furthermore, all of the above irradiators require extensive unpackaging and repackaging of the product from a pallet to the carrier, and following radiation treatment back, onto the pallet for shipping.
Other irradiators have adopted an alternate transport system with which to move a product past a source. In U.S. Pat. No. 5,396,074 there is disclosed a facility for irradiating foods and medical devices using an electron beam as the radiation source. An overhead transport conveyor is used to suspend article carriers to permit their movement around a track and to bring these carriers in front of the radiation source. The suspended article carriers are capable of rotating upon their vertical axes which permits radiation of two sides of a product disposed within the article carrier. This design permits exposure of both sides of the article carrier to the radiation source. However, radiation by electron beam may result in a poor depth of penetration in medium to high density products (i.e. over about 0.4 g/cc), and extensive repackaging is required in order for such products to be treated effectively with a low resulting DUR. This type of irradiator therefore has a limited use. A similar conveying system is found in U.S. Pat. No. 4,481,652 and U.S. Pat. No. 3,673,409, with carriers suspended from a monorail-type track. This system uses cam-catch members that are powered in order to push the product carriers through the labyrinth path before the gamma radiation source.
U.S. Pat. No. 5,400,382 is directed to irradiating products, located on pallets moved on shuttle cars, with gamma rays. The shuttle cars move the pallets into the region of the gamma source, on a series of parallel tracks, and the pallets are transferred from track to track so that each side of the object being irradiated is exposed. Again, with such a design there are many moving parts located within the irradiation chamber thereby minimizing access for maintenance and repair. Furthermore, these irradiators use a source-overlapping-product configuration which results in a low efficiency of radiation utilization.
Several irradiator designs do not require the introduction of the source into the irradiation chamber, rather the product is lowered into the pool surrounding the source. For example, U.S. Pat. No. 3,676,675 is directed to a subterranean production irradiator with a product conveyor system comprising an endless chain and sprockets arranged to permit movement of specialized product carriers past an radiation source. The product carriers are hung from the chain, and pass over and under the source in a sinusoidal path. A similar approach is disclosed in U.S. Pat. No. 4,760,264; 4,908,221; 5,008,550 which incorporates a water-tight duct system through which carriers are passed. The conveyor system comprises a continuous chain in order to move the product through the duct system. In all of these designs, the speed of the conveyor effects all carriers attached to the conveyor, any variation in speed affects all product carriers at the same time throughout the ductwork. Any mechanical problem localized within the subterranean irradiation chamber is also very difficult to repair, and this is complicated by the fact that the source can not be easily removed from the irradiation chamber resulting in time consuming maintenance or repair procedures. Due to the types of carriers employed, extensive product handling in order to load and unload the carriers from, and to, a pallet is required.
U.S. Pat. No. 4,561,358 is directed to an apparatus for conveying elongated articles through an radiation beam. The conveying means comprises two overhead tracks, and a guide that associates with, but is located below the carrier to direct the orientation of the article and permit both sides of the articles to be exposed to the radiation source. U.S. Pat. No. 3,564,241 is directed to an irradiation apparatus comprising a continuous horizontal track to form a single path around a radiation source.
U.S. Pat. No. 4,066,907 discloses the use of a turntable with several levels that circumscribes a vertically placed source. This configuration permits the partial exposure of the top and bottom of the product to the source. The product is moved onto the turntable by a goods handling appliance, such as a fork lift coupled with a telescopic table. The same goods handler is also used to transfer product between levels of the turntable in order to permit exposure of the sides and a portion of the top and bottom of the product to the source. All of this material handling takes place within the irradiation chamber. Due to the harsh environment within the irradiation chamber, routine maintenance requires shutdown of the irradiator. The carriers used within each irradiators also require extensive product handling and repackaging in order to load and unload the carriers. These irradiators also employ a source-overlapping-product configuration which results in a low efficiency of radiation utilization.
Several problems exist with most prior art product irradiators. Many designs require considerable carrier handling within the irradiation chamber either to complete a pass around the source, or to effect a change in the level of turntable or conveyor. Furthermore, several designs require extensive carrier loading and unloading before an after exposure to the source, due to the use of specialized carrier trays used for product radiation. This is especially true if the product is orientation-sensitive and must be loaded in a specific manner prior to treatment. Furthermore, carriers of the prior art do not easily permit variable product heights to be easily loaded or continuously passed around the source. In general, product packaging limitations result in limited flexibility of irradiator use.
A
Gerwing Dave
Perrins Rob
Bruce David V.
Dunn Drew A.
Haynes and Boone LLP
MDS Nordion Inc.
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