INDUSTRIAL IRRADIATION AND STERILIZATION

Food Irradiation Plant Process

The radiation used in processing materials is limited to radiation from high-energy gamma rays, X-rays and accelerated electrons. These types of radiation are called “ionizing” because their energy is high enough to dislodge electrons from atoms and molecules and to convert them to electrically charged particles called ions.

Accelerated electrons:

The electron beam is a stream of high energy electrons, propelled out of an electron gun. This electron gun apparatus is a larger version of a standard television tube. The electron beam

generator can be simply switched on or off. There are no radioactive materials in the process. The electrons can penetrate food only to a depth of three centimeters, or a little over an inch, so the food to be treated must be no thicker than that to be treated all the way through.

Two opposing beams can treat food that is twice as thick. E-beam medical sterilizers have been in use for at least fifteen years.

Gamma rays and X-ray form part of the electromagnetic spectrum, like radio waves, microwaves, ultraviolet and visible light rays. Gamma rays and X-rays are in the short wave length, high-energy region of the spectrum. Both Gamma and X-rays can penetrate foods to a depth of several feet

X-ray is caused by atomic transitions and they are usually less energetic than gamma rays. They have the same properties and effects on materials, their origin being the main difference between them. X-rays with varying energies are generated by machines. The X-ray machine is a more powerful version of the machines used in many hospitals and dental offices to take X-ray pictures. To produce the X-rays, a beam of electrons is directed at a thin plate of gold or other metal, producing a stream of X-rays. Like gamma rays, X-rays can pass through thick foods, and require heavy shielding for safety. However, like E-beams, the machine can be switched on and off, and no radioactive substances are involved. Four commercial X-ray irradiation units have been built throughout the world since 1996.

Gamma rays with specific energies normally come from the spontaneous disintegration of radionuclides. Naturally occurring and man-made radionuclides, also called radioactive isotopes or radioisotopes, are unstable, and emit radiation as they spontaneously disintegrate, or decay, to a stable state. The radionuclide used almost always for the irradiation of food by gamma rays is cobalt-60. It is produced by neutron bombardment in a nuclear reactor of the metal cobalt-59, then doubly encapsulated in stainless steel “pencils” to prevent any leakage during its use in a radiationplant. Cobalt-60 has a half-life of 5.3 years. This technology has been used routinely for more than thirty years to sterilize medical, dental and household products, and it is also used for radiation treatment of cancer. Radioactive substances emit gamma rays all the time. When not in use, the gamma ray “source” is stored in a pool of water which absorbs the radiation harmlessly and completely. To irradiate food or some other product, the source is pulled out of the water into a chamber with massive concrete walls that keep any rays from escaping. Medical products or foods to be irradiated are brought into the chamber, and are exposed to the rays for a defined period of time. After it is used, the source is returned to the water tank.