Although radiation is often associated with nuclear and medical technology in people’s minds, it is a general term used to describe any form of energy that can be transmitted over large distances without special conductors or conduits. For example, the sun radiates both its heat and light through space. Microwave towers radiate energy as signals for TV and mobile phone networks. X-ray machines radiate energy to image body parts. In addition, certain radioactive materials emit radiation of several types. Many sources of radiation, such as the light bulb, have little or no direct effect on the surfaces they illuminate. However other forms of radiation can penetrate and interact with the materials they strike. The sun can burn the skin as its ultraviolet component actually penetrates and deposits energy in the body cells. Likewise infrared and microwave radiation penetrate food and cook it.

X-rays and electron beams are even more penetrating and more dangerous than heat, light and microwaves. Electrons, X-Rays and gamma rays ionize the material they strike by stripping electrons from the atoms of the exposed material. This ionized environment is very damaging to the bacteria, viruses or insects and can also change the chemical structure of materials.

Irradiation is simply the act of applying radiation (or radiant energy) to some material. Irradiation by penetrating electrons, X-rays and gamma rays ionizes materials rather than simply heating them.

Radioactivity is quite a different matter. The natural elements are composed of a nucleus (of protons and neutrons) surrounded by orbiting electrons. For most elements (the stable elements) the number of nuclear particles is fixed. However, a few, equally “natural” elements such as uranium, radium, and thorium come with an unstable number of atomic particles in their nucleus. Periodically these elements eject energy and nuclear particles to achieve a more stable configuration. The energy that is emitted is radiation and the process itself is called radioactive decay or disintegration. The elements that undergo these disintegrations are called radioactive materials. Stable elements can also be made unstable by exposure to intense nuclear radiation as in nuclear power generating plants, nuclear explosions and high energy particle accelerators. In the public mind there is a unclear association between irradiation and radioactive materials (which if leaked or spread would be a health hazard) leading to the erroneous conclusion that irradiation is dangerous.

There are two ways in which radioactive materials are associated with industrial irradiation, and an understanding of the connection shows why any any worries are unfounded. The first connection between radioactivity and irradiation is the radiation source. Radioactive materials are often are used as a source of radiation energy. The most widely used radiation processing source material is an isotope of Cobalt known as Cobalt 60. This is produced by irradiation of pre-encapsulated stable Cobalt 59 in the intense neutron fields of a nuclear power reactor. After irradiation, the Cobalt 60 decays and the energy released in the decay creates a penetrating beam of radiation. When these sources are used it is essential they remain encapsulated and shielded. Provided they are shielded and correctly encapsulated they remain harmless to the public. There is a long record of safe use.

The second way in which radioactivity is discussed in connection with industrial irradiation is mainly a theoretical concern. Radioactive materials can be created when very high energy particles (as created in nuclear reactors and very high energy electron accelerators) bombard a target. In this case, the radiation energy entering the target material can not only ionize it, it can transform a stable element into an unstable one. This is called "induced" radioactivity. After extensive research, it has been established and internationally agreed, that keeping the energy of machine sources below certain well defined thresholds will ensure that any such induced radioactivity will be negligible.

Characteristics Of Electrons, X-Rays And Gamma Rays.

There are three forms of ionizing radiation of practical importance in industrial irradiation, electrons, X-rays and gamma rays.

Electrons, the electrically charged particles that flow in wires as electricity, or strike the face of a television set to make the image, may seem different from the X-ray and gamma ray forms of radiation because they are usually thought of as particles. However, at high energies, beams of electrons can penetrate solid materials and they cause the same ionizing effect. Electron particle beams are therefore referred to as radiation beams even though their particulate nature is somewhat different from the wave nature of an X-ray or gamma ray.

When electron beams strike a target such as a plastic medical device, most of the energy goes towards ionizing atoms and killing micro-organisms. If however, the electron beam is stopped in a very dense material such as tungsten or tantalum, some of the energy stimulates the metal atoms to emit X-rays. These X-rays are more penetrating than their parent electrons but only a portion of the electron power is converted. The effective capacity of the plant with an electron-to-X-ray converter is therefore significantly reduced. X-rays are also spread over a wider angle than an electron beam.

Just as X-rays are formed from atoms excited by the electron beam, gamma rays are formed from atoms that have been excited by nuclear radiation. The physical nature of X-rays and gamma rays is identical, although they may differ slightly in penetration. The different names serve to identify the different origins.

A most important difference between X and gamma rays is that X-rays are only generated when the parent electron beam is “on” so an X-ray source can be switched on and off. On the other hand, once a radioactive gamma ray source has been produced, it will continue to radiate for ever, though with decreasing power over time.

HOME | WHO WE ARE | OUR SERVICES | OUR PRODUCTS | BRIEFING NOTES |  LINKS | CONTACT US