|Gamma sterilization facilities consist of four major component: the biological shield, the safety system, the source system and conveyor system.
|The Biological Shield
Gamma rays pass completely through a product and therefore must be absorbed by a protective biological shield. PT. Perkasa Sterilindo’ gamma sterilization facility uses a concrete cell with ceiling and walls more than 2 meters thick.
Inside the cell the isotope sources are positioned on two parallel racks, store in a water shielding pool more than 6 meters deep. The racks are raised and lowered into operating positions by electric winches.
| The Safety System
A sophisticated, redundant safety system with multiple detectors prevents inadvertent radiation exposure to personnel. Activation of any single detector automatically shuts down the entire system by lowering the source racks safely into storage pool.
Gudes cables are connected to the inside ceiling and pool bottom, and maintain the horizontal positioning of the source racks. The sheaves/source cables hoist, blowers and other equipment located above the cell roof are covered by a mechanically driven roof which can be opened when loading the source casks through the roof. This additional roof was provided to prevent excessive equipment exposure from rain and sunlight.
The racks will be automatically lowered, and the conveyor will be stopped if any of these conditions occur:
De-activation of the emergency stop button.
Violation of the maze entrance photocells.
Violation of the maze pressure mats.
High-level radiation readings in the maze or cell during normal shut down.
Removal of the contained console key.
Loss of electrical power.
Detection of smoke or fire.
Low pool water level.
Breach of the maze doors.
The gamma radiation source is Cobalt-60 which is shipped to the facility in special 6 tonne, lead, accident-tested containers approved by the I.A.E.A. –the International Atomic Energy Association.
The radiation source used, is Cobalt-60 in double encapsulated stainless steel pencils. Each pencil contains approximately 10,000 – 11,000 Curies, which are identified by a unique serial number and are certified to a specific curie content. The pencils are placed into two source racks. The maximum capacities of the source racks are 6,000,000 Curies of Cobalt-60.
|The Conveyor System
The main operating component of a gamma sterilization facility is the conveyor system. Metal carriers positioned on a specially designed overhead monorail system are used to transport product materials around the radiation source racks. This monorail system is controlled by programmable controllers interconnected with diagnostic computers that monitor all function.
During processing operations, radiation from the raised sources kills contaminating organisms anywhere in or on the products, which pass through the gamma cell via the overhead conveyor system. The absorbed dose delivered to the products is a function of the incremental dwell time, the quantity of isotope in the source racks and the density of the product.
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