Gamma Irradiation

                    The applications of the Gamma sterilization

Cobalt 59 is a naturally existing as non-radioactive metal found in various minerals on the earth. After being placed in an intense radiation field, cobalt 59 is transformed into radioactive cobalt 60.  This happens because each nucleus of cobalt 59 absorbs a neutron and becomes unstable.

During the transformation from cobalt 60 back to a stable state, gamma radiation is emitted and the cobalt atoms are reduced to stable nickel metal atoms.

When cobalt 59 becomes cobalt 60, it begins to emit gamma radiation. Unstable nuclei spontaneously emit radiation as they are transformed back to a stable state.  While cobalt 60 is itself unstable, it does not emit gamma radiation of sufficient energy to make its surroundings radioactive.              

Every 5.27 years, cobalt 60 loses 50% of its radioactivity. This is the result of its nuclei becoming stable after emitting gamma radiation. In this way, cobalt 60 is transformed, into stable nickel.                   The radioactive substance cobalt 60 is extensively used in medical and industrial applications. Cobalt 60 is used for medical applications such as in the radiation treatment of malignant tumors and to treat blood. It is also for the irradiation of objects for sterilization purposes.Stable cobalt 59 metal is nickel plated and welded into metal capsules. It is then placed in a high radiation field in a nuclear reactor.                                

The cobalt 59 capsules remain in the reactor for periods of up to five years, at which time a significant amount of it has become cobalt 60 and is producing gamma radiation. Once removed from the neutron field, the already encapsulated source is then welded into another capsule made of stainless steel. Such sources are known as “doubly encapsulated” sources.

These doubly encapsulated cobalt 60 sources have been designed to ensure that they meet very stringent leakage, temperature, pressure, impact, vibration, puncture and bend tests to ensure they remain safe for transport and use during their useful life.

Typically, gamma irradiation plants use cobalt 60 in the form of pencils. The pencils are around 45cm in length, with a diameter of around 8mm. These are grouped into sub-assemblies, which are then placed into a source rack. The source rack is stored in a deep-water storage pool when not in use.

The mechanism of killing organism

Radiation creates free radicals which are highly active chemical compounds. These radicals cut the DNA spiral in the cell of organism. The aim is to create multiple cuts so that the cell is unable to activate its repair mechanisms.

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Sterilization of medical consumables and certain pharmaceuticals

Cold pasteurization of food and pet food

Bio burden reduction of consumer goods. E.g.

  cosmetics and

     toiletries

  pharmaceutical raw

     material

  food packaging

  dyes and colorants

Disinfections of hospital waste

Degradation of toxic wastes and selected polymer resins.

Depolymerization of cellulose

Radiation doping of semiconductors

Coloring of glass and gemstones

Crosslinking of plastics, mainly PE

  by introduction of

   the memory effect

   into heat shrink and

   stretch wrap

   materials

  elimination of

   monomer residues

   from polymers

  generation of foams

   for protective

   clothing

  improving of green

   strength in rubber