Radiation Processing

Where is radiation processing used?

Everyday the radiation processing industry is helping to save lives, maintain health and protect the environment.

Radiation processing is not new. It has been used commercially for almost forty years. Gamma radiation from cobalt-60, electron beams and x-rays, are all used to sterilize the medical devices used in operations and other healthcare treatments. Implants, artificial joints, syringes, blood-bags, gowns, bottle teats for premature baby units and dressings are all sterilized using radiation. 80% of surgical gloves are sterilized using gamma radiation from Co-60. Other industries that benefit from radiation processing include the food, pharmaceutical, cosmetic, horticultural, and automotive industries. A recent application is the irradiation of feathers for use in bedding, to protect users from the avian flu virus. In the horticultural industry, growing-mats, fleeces and pots may be reused after irradiation - reducing waste and cost and saving the environment from unnecessary waste. Similarly, commercial egg trays may be recycled after irradiation without risk of proliferating salmonella.

Why Irradiate?

Irradiation has three main applications: The treatment of products such as medical devices, food, packaging and waste materials to kill bacteria and sterilize or in the case of food pasteurize the product; the treatment of export bulk commodities such as tropical fruits to extend shelf life by slowing the ripening process and inhibiting sprouting and to kill quarantine pests such as fruit flies; the treatment of polymeric materials to modify their physical properties.

Irradiation is an especially effective sterilization method because radiation penetrates through product packaging and even passes through to the inside of the product without leaving unwanted residues behind. Products with complex physical forms and high surface areas such as syringes, dressings and theatre packs are sterilized inside their final packaging and are fit for use immediately after irradiation. In addition, the efficacy of herbal substances is diminished far less by treatment with radiation than by thermal or chemical methods. For example, herbal materials used in pharmaceuticals and cosmetics often have a high bacterial content and their effectiveness is diminished by heat sterilization. In the automotive industry irradiation is used to improve the physical properties of components used in cars.

How does it work?

Radiation processing uses highly penetrating x-rays or gamma radiation from sealed radiation sources or a stream of high-energy electrons, travelling at almost the speed of light, to bombard and kill bacteria in products sealed inside their final packaging. In this way the irradiated product remains sterile until the packaging is removed. X-rays, gamma radiation and electron beams sterilize products by exactly the same mechanism of ionisation. The main difference between E-beams and radiation is in the depth of penetration. Since electrons have both mass and charge the penetration depth is approximately ten times less than gamma and X-rays, e.g. 8 cm compared with 80 cm in typical use for radiation processing. This limits E-beam to the treatment of individual packages while gamma and x-rays can treat palletised product.

The energy carried by the radiation or the E-beam is transferred to the product being irradiated by collisions between the radiation or electrons and the atoms of the product. In these collisions atoms lose their bound electrons in a process called ionisation. It is this process that results in irreparable damage to the life sustaining chemistry of living organisms and the initiation of cross linking chemistry in polymeric materials.

>> More about Key Processing Parameters

Is Radiation Processing safe?

There is no denying that without skilled engineers and trained operators and without the correct facilities and procedures radiation processing is potentially hazardous. However, this is a highly regulated industry that has been operating safely for more than forty years on the business parks we drive past everyday. Routine workers in these facilities wear normal everyday clothing and comply with standard Health and Safety at Work legislation.

What Happens in an Irradiation Plant?

Because the radiation and electrons used are highly penetrating it is necessary to irradiate products in a shielded environment to prevent radiation from passing into the surroundings. This is usually a concrete room, called an irradiation cell, contained within a warehousing facility.

In a gamma irradiation cell the sealed radiation sources are kept in a source rack in a pool of water 6m deep. With the source rack in this position the water absorbs the gamma radiation and people can enter the cell wearing everyday clothing without risk of being irradiated or contaminated. The water is pure enough to drink! The source rack is only raised when the cell is isolated and sealed. The walls of the irradiation cell are 6 feet thick, constructed of high density concrete to prevent radiation from penetrating into the surrounding environment. The product to be treated is loaded into carriers on a conveyor that passes into the cell through a labyrinth. They pass slowly by both sides of the raised source to ensure that the product receives an even dose of radiation throughout. After an appropriated time in the cell the product leaves via the labyrinth to be removed from the carriers and shipped out of the warehouse for use.

Is there a risk of product contamination?

How do we know that a product has been irradiated?