Radiation Processing Basics
Electrons & X-rays
Energy,power,dose
Accelerators
Radiation effects
Crosslinking
The Industry
Food Irradiation
Online Sterilization

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Effect Of Radiation On Materials

High energy electrons react with materials by stripping loosely bound electrons to create a positively charged ion (ionization) with a free electron. An ionized atom (otherwise called a free radical) can either collide with a free electron and become neutral again (de-ionize) or react chemically. Free radicals are extremely chemically active and may either degrade or enhance products depending on the reactions that dominate. These chemical reactions have led to the use of radiation for a number of industrial purposes.

The Radiation Processing Industry

The irradiation industry is broadly defined to include the processing of materials by gamma radiation and industrial accelerators. Materials which use irradiation as part of their manufacturing process today include medical products, plastics, rubber, wire and cable, some spices, and a small volume of certain food products.

Service centres currently handle medical sterilization, specialty polymers, degradation of Teflon®, specialty wire and cable, gemstones, spices, and laboratory animal feed.

The sterilization of medical products such as surgical gowns, gloves, and syringes composes the bulk of the market for materials processed by highly penetrating radiation today. The size of the market was estimated (in 2000) at 325 million cubic feet of product sterilized annually in North America, and at least 650 million cubic feet globally. There are currently over 50 irradiation facilities in North America, with about half being operated in house by manufacturers and the remainder operated by contract service firms who process products manufactured by other companies for a fee.

As of 2002 there were 29 contract irradiation plants (20 cobalt 60 and 9 electron beam) in North America. There are a number of companies currently operating service centres, the largest being Steris (Isomedix) and Sterigenics International in the U.S. and Isotron plc in Europe.

Sterilization

Sterilization of medical products is presently served by three main technologies - ethylene oxide, gamma radiation (cobalt 60), and electron accelerators. Ethylene oxide sterilisation is an effective and long established method which accounts for more than 50% of the medical sterilization market in the U.S. It is used whenever the product properties would be adversely affected by radiation. It cannot be used on hermetically sealed packaging, on items with sealed inner cavities and where residues are of clinical importance. Cobalt 60, a commercially made isotope, is the industry standard for radiation sterilization and gained market share from ethylene oxide in the 1970’s to 1990’s.

The technology is well established and is cost effective at medium volume levels. However, electron accelerators can be more cost effective at higher throughputs. Electron accelerator technology has been in existence for some decades though only in recent years have higher energy and higher power electron beam accelerators been developed for sterilisation plants. The effect of radiation on the medical products is important as this energy may cause crosslinking or degradation of plastics. Special, radiation resistant materials have been formulated for a large number of products.

Typical Electron Beam Plant

In a typical sterilization plant designed for high volume processing, products enter on a conveyer through a labyrinth that permits access but stops radiation from escaping. The treatment room houses the accelerator itself and, like the whole installation, is constructed of thick concrete to protect workers from radiation. In the treatment room the materials pass under the accelerator for processing. Once the materials have been “sprayed” with electrons, they continue on the belt until they exit the installation. The equipment area contains the electrical, electronic and cooling equipment required to run the accelerator.

Inline sterilization

The high cost of electron accelerators and the shielding shown above has led to an industry where there are relatively few contract service centers, each with a very large capacity to sterilize or otherwise process products. This means transportation costs can be high compared with sterilization costs and there may be delays in processing as clients wait for time to be allocated to their product.



Many producers of medical devices would prefer to keep their product in-house and to have their own radiation sterilizer. There have been several in-line sterilizers built. In-line sterilizers use lead or steel shielding rather than concrete and limit the power and penetration of the accelerator. These limitations mean that products are treated in their sealed packages but before they are boxed. In-line sterilizers have lower capital costs than the large contract service centers but the cost to sterilize each item is higher. For high value products, this cost is more than balanced by the benefits

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