Applications of radioisotopes have come a long way since their first practical use over a century ago. One of the most common applications of radioactive sources is sterilization of healthcare products, including medical devices and pharmaceuticals. Radiation sterilization can penetrate products while sealed in their final packaging, which simplifies the manufacturing and distribution process. Implantable devices (orthopaedics, stents, etc) as well as tissue-based devices coming from human donors, are also commonly sterilized with cobalt-60 to increase patient safety. Given the huge volume of devices which need to be sterilized, this processing is typically done in large commercial gamma facilities containing MCi (tens of PBq) quantities of cobalt-60.
High activity sources are also used for food safety and preservation and phytosanitary applications. To extend food's shelf-life during transport and storage, it needs to be preserved. In addition, transported produce needs to be free of pests that could disrupt the environment or agricultural regions where it is received. In many countries, food irradiation with cobalt-60 is routinely used to prevent sprouting or rotting, to delay ripening, and to reduce the risk of foodborne illness. Sterile Insect Technique (SIT) is another common application of gamma sources. This insect control method involves radiation sterilization of target pests, followed by the systematic area-wide release of the sterile males to mate with wild females without producing offspring. SIT has proved to be successful by eradicating several insect pests in various regions worldwide.
Hundreds of self-shielded cobalt-60 installations (with up to 100 kCi of cobalt) are estimated to be present worldwide in research institutes, universities, and government laboratories. However, due to their low activity, these setups are rarely used for industrial applications. Larger (few hundred kCi) cobalt-60 research irradiators are even less common than self-shielded cobalt units, however, a few dozen such facilities are installed worldwide. A typical facility consists of a concrete bunker with a source pool (or source rack) in the middle. Products to irradiate are usually placed around the source, sometimes on turntables. This setup can accommodate larger volumes of samples compared to self-shielded units.
Industrial cobalt-60 irradiators are primarily used for food or phytosanitary applications and medical device sterilization. They operate in either continuous or, less commonly, in large batch mode, and products to be irradiated come in pallets or tote boxes. Food irradiation requires relatively low doses: less than 1 kGy to inhibit the growth of sprout, slow the ripening process, and kill insects and larvae that can be found in grains, fruits, and vegetables after harvesting; and up to 10 kGy to destroy pathogens in meat and fish, control molds and extend shelf life in fresh products. Therefore, food irradiation typically uses small (~1 MCi) industrial irradiators, which can rapidly provide 1 -10 kGy doses. Large industrial irradiators (greater than 1 MCi) are almost exclusively used for medical device sterilization as they can deliver high doses required for medical products (25 – 50 kGy) at high speed. If needed, they can also be used for food or phytosanitary applications with a split source rack. It is estimated that about 500 MCi of cobalt-60 installed at about 200 facilities.
