How Do Irradiators Work?

• Radiation – energy traveling through space in the form of high speed particles and electromagnetic waves
• Ionizing radiation – radiation with enough energy to make ions or charged particles
• Non-ionizing radiation -  radiation without enough energy to ionize atoms (visible light, ultra violet UV, radio and television waves, and microwaves)
• Irradiation – exposure to ionizing radiation
• Dose – the quantity of radiation absorbed

How is Irradiation Done?

Food is irradiated by exposing it to ionizing radiation. Radiation is a household word that covers a wide spectrum of energy, ranging from low-level emissions from TV sets and computer screens to deadly gamma rays from nuclear fuel and waste products. High energy radiation can change the structure of a molecule. Electricity also can be used to produce ionizing radiation, as is the case with X-ray Machines or linear accelerators. Whether ionizing radiation comes from radioactive materials or linear accelerators, its effect on food is the same; the only difference is how the radiation was produced.

In a typical food irradiation process, gamma rays from the radioactive isotope Cobalt 60 are used to destroy the DNA of disease-causing microorganisms. The effect of irradiation on microorganisms depends on the power of the rays, as well as the amount of time food is exposed to them.

Irradiation exposes food to ionizing radiation using one of three sources: gamma rays (produced by Cesium 137 or Cobalt 60), X-rays and electron beams (or “e-beam”). Electron-beams are produced by using a linear accelerator developed by defense contractor Titan Corp. for the Star Wars missile-defense program.

Gamma Ray Facilities

In the Cobalt 60 process, there are four different categories of irradiators which refer to how the isotope source is stored and shielded:

• Category I, small sources used in research
• Category II, air storage and air irradiation; not used for food
• Category III, water shielding and irradiation under water
• Category IV, water storage but moves into air to irradiate

For Category IV irradiators (most gamma ray facilities are of this type) trays of food are placed inside tall aluminum towers mounted on remote-controlled tracks. An operator in a control room moves the food-carrying towers into a chamber protected by six-food-thick concrete walls, where a rack of radioactive Cobalt 60 “pencils” is immersed in a pool of water 28 feet deep. This rack of Cobalt rises out of the water, and the aluminum towers containing the food rotate around it.

Sometimes food irradiation proponents compare food irradiation facilities to medical facilities. This is misleading. Food irradiation facilities usually use around 5-15 million curies of Cobalt. Nuclear medicine facilities seem to use various materials with only a few hundred to a few thousand curies.

Comparison of Sources

Gamma radiation is preferred because it can penetrate deeply, while “e-beams” penetrate food to a depth of only one-and-a-half inches. X-rays are capable of irradiating thicker items, but the process is extremely expensive and energy intensive. Large amounts of food would have to be irradiated to make it affordable.